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Glossary List
  • 35S Promoter
    The promoter region of a gene from a Cauliflower mosaic virus. This promoter induces gene expression in all cells all of the time.
  • A Horizon
    Mineral horizons which formed at the surface or below an O horizon and which exhibit obliteration of all, or much, of the original rock structure and are: (1) characterized by an accumulation of humified organic matter intimately mixed with the mineral fraction and not dominated by properties characteristic of E or B horizons; or (2) have properties resulting from cultivation, pasturing, or similar kinds of disturbance. (SSSA)

  • Absorption
    Process of moving a substance from the exterior of a plant to the internal portion.
  • Absorption
    The process of moving a substance from the exterior of a plant to the internal portion.
  • Absorption
    Process of moving a substance from the exterior of a plant to the internal portion.
  • ACC Oxidase
    The enzyme in the ethylene biosynthesis pathway converting ACC (1-aminocyclopropane-1-carboxylic acid) to ethylene.
  • ACC Synthase
    The enzyme in the ethylene biosynthesis pathway converting SAM (S-adenosyl-methionine) to ACC (1-aminocyclopropane-1-carboxylic acid).
  • ACCase
    acetyl-Coenzyme A carboxylase; enzyme responsible for production of fatty acids and is the target of many herbicides that have the lipid synthesis inhibitor mode of action.
  • Acid
    A chemical compound that can donate a proton
  • Acidic
    Having a pH lower than 7, having a higher concentration of H+ ions.
  • Acido
    Un compuesto químico que tiene la capacidad de donar un protón (H+).
  • Acrylamide
    Chemical with the basic formula C3H5NO that can be chemically induced to form a gel matrix. This matix can be used for electrophoretic separation of proteins and nucleic acids.
  • Action Site
    A location in dense vegetation, that will collect water droplets and ensure a high degree of moth survival. The area where mating between male and female moths occurs.
  • Active Site
    The location on an enzyme (protein) to which substrate molecules bind and are converted to their products. The shape of this site must be maintained for the enzyme to remain functional.
  • Addition
    The movement into or deposition of a quantity of material.
  • Additive
    Adjuvant; any of several categories of compounds that can be added to a herbicide solution to enhance its activity.  Some examples are oils, surfactants and fertilizers.
  • Adhesion
    A molecular attraction between a surface and solvents and solutes in contact with it
  • Adjuvant
    An additive.  Any of several categories of compounds that can be added to a herbicide solution to enhance its activity; some examples are oils, surfactants and fertilizers.
  • ADN
    (Acido desoxiribonucleico; DNA en inglés). La molécula que almacena la información genética. Está compuesta por una doble hélice cuyas cadenas se mantienen unidas entre sí por enlaces débiles formados entre pares de nucleótidos adyacentes. El ADN es la materia básica de la que están formados los genes.
  • Adsorption
    The process of a substance binding to a surface.
  • Adult
    A fully grown, mature organism.
  • aeolian
    wind transported materials
  • Aeration
    The condition and sum of all processes affecting soil pore-space gaseous composition, particularly with respect to the amount and availability of oxygen for use by soil biota and/or soil chemical oxidation reactions.
  • Aerobic
    Condition that has ample amount of oxygen. This condition will allow organisms that require molecular oxygen to growth and function well.
  • AFLP
    Amplified Fragment Length Polymorphism. A molecular marker method consisting of (1) DNA cleavage with two restriction enzymes, (2) ligation to synthetic linkers, and (3) two PCR amplification steps using primers 16 to 17 bases in length. The technique results in a large number of DNA bands per analysis (50 to 100 are commonly observed), and thus it can be an efficient way of detecting polymorphic loci. However, the large number of bands can be difficult to score. AFLPs are usually dominant and require no prior genome information. Because AFLP bands are "anonymous" (i.e., their chromosome positions are not known in advance), RFLP or SSR markers are sometimes evaluated in the same population in order to "anchor" the AFLPs to specific chromosome arms. AFLPs can be detected either with radioactive label or silver staining. The technique is described in more detail in S. Grandillo and T.M. Fulton (2002), Approaches to gene mapping. In P.M. Gilmartin and C. Bowler (ed.) Molecular Plant Biology Vol. 1. Oxford Univ. Press, Oxford and New York.
  • Agarose
    A carbohydrate powder purified from sea weed that can be boiled and cooled into a semi-solid matrix.
  • Aggregates
    Soil particles glued or cemented together. The agents responsible for cementing particles include organic matter and calcium carbonates.
  • Agrobacteria
    A soil bacteria that can be a plant pathogen. It works as a natural genetic engineer by invading a plant through wounds and inserting a piece of DNA into the plant's chromosomes. The plant will then begin producing the protein encoded by the inserted gene. Bacillus thuringiensis is a strain of agrobacteria.
  • Agrobacterium
    A soil bacteria that can be a plant pathogen. It works as a natural genetic engineer by invading a plant through wounds and inserting a piece of DNA into the plant's chromosomes. The plant will then begin producing the protein encoded by the inserted gene. Bacillus thuringiensis (Bt) is a strain of agrobacteria.
  • Air-filled Porosity
    The percent of air occupying the empty spaces of soil and is inversely related to the percent of water occupying the empty spaces of soil. Total porosity= air-filled porosity plus water-filled porosity.
  • Algorithm
    A mathematical equation used to make a prediction, for example, predicting fertilizer requirement from soil analysis and anticipated crop yield.
  • Alkaline
    Basic; having a pH higher than 7; having a lower concentration of H+ ions.
  • Allele
    One of the different forms of a gene (or marker) that can exist at a single locus. A single allele for each locus is inherited separately from each parent.
  • Allelic
    An allele is one of a pair or series of forms of a gene possible. An example of allelic variation would be a dominant vs recessive allele for one gene.
  • Allergen
    A biological or chemical substance that elicits a reaction involving the body's immune system.
  • Alluvium
    Sediments deposited by the running water of streams or rivers. Alluvium may occur on terraces well above present streams, on the present flood plains or deltas, or as a fan at the base of a slope. (SSSA)

    Acetolactate synthase or acetohydroxy acid synthase; an enzyme essential for amino acid production and is the target of many herbicides including the imidazolinones and sulfonylureas; this enzyme has mutated in some species to become herbicide resistant
  • Aluminum Oxides
    Group name for the oxides and hydroxides of aluminum. Includes the minerals gibbsite, bauxite.
  • Aminization
    The process by which microorganisms break down complex proteins to simpler amino acids, amides, and amines.  Aminization is the first step of mineralization as part of the nitrogen cycle.
  • Amino Acid
    The basic building blocks of proteins. The sequence of amino acids is a protein and protein function are determined by the genetic code. It is an organic molecule containing a carboxyl group and an amino group.
  • Amino Acid Synthesis Inhibitors
    A mode of action of herbicides that inhibit the production of essential amino acids.
  • Aminoácido
    Una molécula orgánica que contiene un grupo carboxilo y un grupo amino; es un monómero que forma parte de las proteínas.
  • Aminoácidos
    Las unidades básicas para la síntesis de las proteínas. Tanto la secuencia de los aminoácidos en una proteína, como la función de la proteína, están genéticamente determinadas.
  • Aminoácidos aromáticos
    Aminoácidos cuya grupo "R", o cadena lateral, contiene un grupo aromático (derivado del benceno). Como ejemplo se tienen fenilalanina, tirosina y triptófano.
  • Ammonia
    One of the mineral forms of nitrogen in the gas form NH3.
  • Ammonia Volatilization
    The process by which ammonia is lost to the atmosphere.  Volatilization occurs when ammonium in the soil, because of its pH, is converted to ammonia, which dissipates as a gas.
  • Ammonification
    The release of ammonium (NH4+)ions from organic matter via microbial action (more broadly termed mineralization)
  • Ammonium
    One of the mineral forms of nitrogen. NH4+
  • Ammonium Nitrate
    A dry granular material manufactured by reacting nitric acid with anhydrous ammonia. One-half of the nitrogen in ammonium nitrate is in the nitrate form, and one-half is in the ammonium form.
  • Ammonium Nitrate-Sulfate
    A dry nitrogen fertilizer (30-0-0 + 6.5S) manufactured by reacting anhydrous ammonia with a mixture of nitric acid and sulfuric acid; good storage and handling characteristics.
  • Ammonium Phosphate
    A material produced by reacting ammonia with phosphoric acid or a mixture of phosphoric and either sulfuric or nitric acids.  Ammonium phosphate is the leading nitrogen-phosphorus product in the fertilizer industry; high analysis, high water solubility, good physical characteristics and low production costs.
  • Ammonium Sulfate
    A dry crystalline material (21-0-0 +24S) produced by reacting anhydrous ammonia with sulfuric acid; stores well.  An excellent choice when both nitrogen and sulfur are needed.
  • Ammonium Thiosulfate Solution (ATS)(12-0-0+26S)
    The most commonly used source of sulfur in fluid fertilizer; weighs 11.5 lbs./gal. After application to the soil, thiosulfate is decomposed to form approximately equal amounts of sulfate sulfur and elemental sulfur.
  • Amorphous Wax
    Smooth or glasslike wax occurring on leaf surfaces and is generally easy to wet.
  • Amplification
    An increase in the number of copies of a specific DNA fragment.
  • Anabolic
    Synthetic processes resulting in the production of complex products.
  • anaerobic
    1. The absence of molecular oxygen (O2). 2. Anaerobic soil -- a condition that exists in soils when they are flooded or compacted.
  • Anaerobic
    Condition that is lacking molecular oxygen. Under this condition, organisms that do not require molecular oxygen will survive and funtion well.
  • Androecium
    Stamens as a group
  • Angiosperm
    A plant which flowers and forms fruits with seeds; seeds are enclosed in a pericarp.
  • Anhydrous Ammonia
    A gaseous material that is compressed and stored as a liquid. At 60oF, a gallon of anhydrous ammonia weighs 5.15 pounds. Due to the fact anhydrous ammonia needs to go through the nitrification process, it is more resistant to losses from the soil by leaching or denitrification because it is converted by bacterial action to the nitrate form more slowly than are other nitrogen sources.
  • Anion
    A negatively charged ion.
  • Anionic
    Having a negative charge.
  • anisotropic
    Not equal in all directions; having a preferred or dominant direction.
  • Annotated
    Annotations are the descriptive information, references to published articles, and other explanatory material that are added to a gene sequence.
  • Annual

    Living or growing for only one year or season.

  • Antagonism
    Reduced activity of one or more herbicides when applied together compared to applying them individually
  • Antagonist
    A non-phytotoxic chemical that can protect the crop from herbicide injury without reducing the damage imposed on the weed; the mechanism of safening can involve induction of enzymes which metabolize the herbicide in the protected crop; also known as safeners, antidotes or crop protectants.
  • Antagonize
    To bother.
  • Antena
    Un pigmento cuya función primaria es la captura de energía de los fotones y su transferencia a otros pigmentos dentro del fotosistema del cual forma parte. La mayoría de las moléculas de clorofila funcionan como antenas; solo unas pocas de los cientos de moléculas de clorofila que forman parte de un fotosistema realizan reacciones fotoquímicas en el centro de reacción. Los carotenoides también funcionan como antenas; adicionalmente, juegan un papel importante en la extinción de moléculas de clorofila en estado triplete y de oxígeno en estado simple que podrían causar daño a las células vegetales.
  • Antenna
    A pigment with the primary function of capturing the energy from photons and transferring that energy to other pigments within the photosystem. Most chlorophyll molecules function as antennae, with relatively few of the hundreds of chlorophyll molecules carrying out photochemistry in the reaction center. Carotenoids also function as antennae, but additionally play an important role in quenching triplet chlorophyll and singlet oxygen molecules that would cause damage to the plant cell.
  • Anther
    Part of the stamen that bears the pollen.
  • Anthers
    The part of the stamen (part of the male reproductive structure) that develops and holds pollen; supported by the filament
  • Anthesis

    The period during which a flower is fully open and functional.

  • Anthropogenic
    The effects of human influence/activities on nature.
  • Antibody
    Immune system protein made by mammals to specifically bind to foreign molecules allowing the mammal to fight off disease.
  • Antigen
    A molecule which trigger's an immune system to create an antibody to bind to it.
  • Antisense RNA
    A synthetic mRNA molecule with the opposite, or complementary, sequence of the actual in vivo molecule. The antisense version will bind to its counterpart and thus reduce or abolish gene expression.
  • Aonocots

    A subclass of Angiosperm plants based on anatomical characteristics.
    They tend to have:

    -Narrow leaves
    -One cotyledon
    -Parallel veins in the leaves
    -Flower parts are usually in multiples of threes
    -A scattered arrangement of primary vascular bundles in the stem
    -Fibrous root system

    ex. grass, daylilies, corn

  • Apical meristem

    tissue at the tip of a plant shoot that causes new growth.

  • Apomixis

    Seed reproduction but not dependent on fertilization.

  • Apoplast
    Regions or cells in the plant not bound by a membrane (i.e. the cell wall region between cells or xylem tissue; apoplastic means 'non-living' tissue. 
  • Apoplastic Path
    Water moves in the cell wall or non-living region between cells without crossing any membranes. Apoplastic means 'non-living' tissue.
  • Aqua Ammonia
    Anyhdrous ammonia dissolved in water. It is a low pressure solution and contains free ammonia, the amount of which increases as air temperature increases.
  • Aromatic Amino Acids
    Amino acids whose side chains chemical structures contain an aromatic ring. Examples include phenylalanine, tyrosine and tryptophan.
  • Aspect
    The predominant direction of slope of the land.
  • ATP
    Adenosine 5'-triphosphate
  • Autoclaving
    A treatment of solutions, tools and containers with high temperature (usually at 120oC) under high pressure (usually at 1.05 kg/cm2) to eliminate organic contaminations.
  • Autotroph
    An organism that can use CO2 as its principle carbon source.
  • Auxin
    Indole-3-acetic acid (IAA); the first plant hormone discovered; a plant hormone involved in many plant growth processes including embryo development, root and flower development, vascular differentiation, stem elongation, apical dominance and tropic response.
  • Auxin-Binding Protein (ABP)
    A 22 kDa protein located in the endoplasmic reticulum which is thought to recognize auxin and act as a receptor at the cell surface.
  • Auxina
    Acido indol-3-acético (IAA); la primera fitohormona descubierta. Una fitohormona involucrada en muchos procesos del crecimiento vegetal, incluyendo el desarrollo del embrión, desarrollo radicular y floral, diferenciación vascular, elongación del tallo, dominancia apical y los tropismos.
  • Auxinic Herbicide
    The first selective organic herbicides developed. This family of herbicides is described as synthetic auxins, growth regulators with herbicidal action, or herbicides with growth regulatory activity.
  • available soil water

    the portion of water in the soil that can be readily absorbed by plant roots. Available soil water is most important for crop production. It is the water held by he soil between field capacity and permanent wilting point.

  • Available Water
    (Capacity) The amount of water released between in situ field capacity and the permanent wilting point (usually estimated by water content at soil matric potential of –1.5 Mpa). Available water is not the portion of water that can be absorbed by plant roots, which is plant specific. (Soil Science Society of America, 1997, p. 9)
  • available water capacity

    the amount of soil water that a soil of a given texture can hold; measured in inches per foot of depth. It is commonly defined as the difference between the amount of soil water at field capacity and the amount at wilting point.

  • Axillary bud

    a bud growing from the axil of a leaf (where the leaf connects to the stem).

  • B Horizon

    Horizons that formed below an A, E, or O horizon and are dominated by obliteration of all or much of the original rock structure and show one or more of the following:

    1. illuvial concentration of silicate clay, iron, aluminum, humus, carbonates, gypsum, or silica, alone or in combination;

    2. evidence of removal of carbonates;

    3. residual concentration of sesquioxides;

    4. coatings of sesquioxides that make the horizon conspicuously lower in value, higher in chroma, or redder in hue than overlying and underlying horizons without apparent illuviation of iron;

    5. alteration that forms silicate clay or liberates oxides or both and that forms granular, blocky, or prismatic structure if volume changes accompany changes in moisture content; or

    6. brittleness. (SSSA)

  • Bacillus thuringiensis
    The soil bacteria which naturally produces the Bt protein toxic to European corn borer (ECB).
  • Backcross
    A breeding method used to move one or a only a few desirable genes from an agronomically poor crop line to an elite line. This is done by crossing a donor parent to an elite line, and crossing offspring with the 'desired gene(s)' back to the elite parent.
  • Backcross Breeding
    After a plant has been transformed, the event must be moved into an elite genetic background. This is done by mating the transformed plant back to elite plants over several generations.
  • Backcrossing
    A breeding method used to move one or only a few desirable genes from an agronomically poor crop line to an elite line. This is done by crossing a donor parent to an elite line, and crossing offspring with the 'desired gene(s)' back to the elite parent.
  • Banda de Caspari
    Una capa cerosa constituida de suberina repelente al agua que cubre las paredes celulares de la endodermis a lo largo y ancho de las raíces de las plantas.
  • Bar Gene
    Also called the PAT gene; it is the bacterial gene that encodes the protein phosphinothricin (PAT) which detoxifies the Liberty herbicide molecule resulting in Liberty resistance.
  • Barrenador Europeo del Maíz
    Ostrinia nubilalis (Hübner) es un insecto plaga de importancia en maíz, que anualmente cuesta a los agricultores millones de dólares por conceptos de control y disminución de los rendimientos. La larva del barrenador Europeo del maíz se alimenta de las hojas y perfora los tallos.
  • Basal bud

    buds at the crown of a plant capable of producing new tillers.

  • Base
    A chemical compound that accepts a proton.
  • Base Pair
    A pair of nucleotide bases in the double stranded DNA double helix structure. Base pairs form the 'rungs' on the DNA ladder. A single base pair is made when Adenine from one DNA single strand binds with Thymine in the other strand or when Guanine from one strand binds with Cytosine in the other.
  • base saturation
    The ratio of the quantity of exchangeable bases (mostly Ca, Mg, K, Na) to the cation exchange capacity expressed as a percent. The cation exchange capacity is the sum of exchangeable bases plus total soil acidity (H, Al) at pH, values of 7.0 or 8.0.
    (SSSA Glossary of Soil Science Terms)
  • Basepair
    A pair of nucleotide bases in the double stranded DNA double helix structure. Base pairs form the 'rungs' on the DNA ladder. They are made when Adenine from one DNA single strand binds with Thymine in the other strand or when Guanine from one strand binds with Cytosine in the other strand.
  • Basic
    Having a pH higher than 7, having a lower concentration of H+ ions.
  • Basipetal
    Unidirectional transport from the apex to the base.
  • Basípeto
    Transporte unidireccional del ápice hacia la base de la planta.
  • BC 1 Generation
    (Backcross) 1 generation is the offspring resulting from the first cross back to the recurrent parent in the backcross breeding method.
  • Bearing Strength
    The average laod per unit area required to rupture a supporting soil mass.  Measured in units of kg m-2.
  • Benzoic Acids
    Family of herbicides that have activity on synthetic auxins belonging to the growth regulators mode of action.
  • Biennial
    A plant that normally requires two seasons to complete its life cycle, growing usually as a rosette in the first season and producing flowers and fruits and then dying in the second season.
  • Biliabate

    Divided into two upper lobes.

    side view of flower, showing upper and lower lobes front view of flower, showing two lobes above
    side view front view


  • Bioinsecticide

    A chemical or substance produced within the plant that kills an insect.  In the case of Bt corn, the insecticide is a protein produced because a gene has been added to the DNA of the corn plant.

  • Biolistics
    A method for introducing DNA into a target organism using high-speed particle bombardment.
  • Biolística
    También conocida como bombardeo de microproyectiles y aceleración de partículas. Un método empleado para transformar células usando micropartículas de oro o tungsteno recubiertas de ADN que son literalmente disparadas hacia dentro de la célula.
  • biomass
    (i) The total mass of living organisms in a given volume or mass of soil. (ii) The total weight of all organisms in a particular environment.
  • Biomolecules
    Molecules, usually organic molecules, found in cells and living organisms
  • biota
    plants and animals including microbes

  • Biotic Factors
    Biological aspects of the environment, one of the conventionally accepted soil forming factors.
  • Biotransformation
    Change in the herbicide's chemical structure within plant cells.
  • Blade

    linear elongated leaf.

  • Bolting
    Flower stalk elongation.
  • Boot stage

    the stage of plant growth when the seed head begins to push through the upper leaf sheath.

  • Boundary Layer
    A region of still air near the surface of a leaf through which water must diffuse en route to the atmosphere.
  • Branched-Chain Amino Acids
    Amino acids whose side chain chemical structrue is branched. Examples include leucine, isoleucine and valine.
  • Bray-P1
    Chemical extraction method developed by R.H. Bray and L.T. Kurtz in 1945 to estimate the availability of P to plants.
  • Bt

    Bacillus thuringiensis, a bacteria that produces a protein that is toxic to certain insects.  The term is often used loosely to represent either the gene or the associated protein created within a plant that has been genetically modified to carry the gene.

  • Bt Corn
    Corn that has been transformed with the Bt gene and is resistant to European corn borer.
  • Bt Corn Hybrids
    Corn hybrids that have been transformed with the Bt gene and are resistant to European corn borer (ECB).
  • Bt Gene
    A gene originating from the Bacillus thuringiensis soil bacteria that encodes a protein toxic to the European corn borer (ECB).
  • Bt Protein
    Another name for the CrylA proteins. These proteins occur naturally in Bacillus thuringiensis bacteria and are toxic to the European corn borer (ECB).
  • Buffer pH
    A test used to estimate lime requirements in soil, which means the amount of agricultural lime required to neutralize the H+ from the soil exchange sites and in the soil solution.
  • Buffer Strips
    Vegetated areas designed to allow runoff to pass through the strips for filtration, sedimentation and adsorption of nutrients.
  • Bulbils
    Small bulb or bulb-like structure found in the place of a flower or leaf axil of a plant; found on tiger-lilies.
  • Bulbs
    Fleshy, specialized underground stem modified for storage and surrounded by modified leaves called scales, i.e., tulips.
  • Bulk Density
    The dry weight of soil per unit volume of soil; most often expressed on a soil volume basis, rather than on a particle basis. Bulk density considers both the solids and the pore space; whereas, particle density considers only the mineral solids.
  • Bunchgrass

    a grass that grows in a more upright fashion creating “bunches” as opposed to spreading out laterally.

  • C Horizon
    Horizons or layers, excluding hard bedrock, that are little affected by pedogenic processes and lack properties of O, A, E, or B horizons. (SSSA)
  • C:N Ratio
    The amount of carbon in organic material divided by the amount of total nitrogen in the same organic material.
  • Calcium Sulfate
    A byproduct of manufacturing concentrated superphosphate; contains 15-18 percent sulfur.
  • Calcium-Calmodulin
    A regulatory protein that has four high-affinity calcium binding sites. The calmodulin-calcium complex can bind to and activate several enzymes.
  • Calibration (Soil Test)
    The process of determining the crop nutrient requirement at different soil test values.
  • Callus
    A mass of undifferentiated cells used in tissue culture.
  • Calyx
    The sepals collectively, directly below the corolla.
  • Canales
    Un tipo de proteínas de transporte que conforman poros selectivos en las membranas de las células a través de los cuales las moléculas pueden difundirse
  • Canopy

    when the upper part of leaves spread out in such a way to shade or cover the ground.

  • Capa Límite
    Una región de aire inmóvil sobre la superficie de las hojas a través de la cual el agua debe difundirse en su ruta hacia la atmósfera
  • Característica
    El atributo que resulta de la expresión de uno o mas genes. Por ejemplo: hojas erectas, tolerancia a sequía, resistencia a Bt. Una característica puede ser influenciada por el ambiente.
  • Carbon/Nitrogen (C/N) Ratio
    The ratio of the mass of organic carbon to the mass of organic nitrogen in soil, organic material, plants, or microbial cells.
  • Carbonation
    Reaction with carbonic acid.
  • Carbonic Acid
    A weak acid formed when water combines with carbon dioxide.
  • Carotenoid
    A plant pigment that protects chlorophyll from being photodegraded; enzymes that aid in the production of carotenoids are the target site of herbicides belonging to the pigment synthesis inhibitor mode of action.
  • Casparian Strip
    A ribbon-like layer of water-repellent suberin (waxy layer) that is wrapped around the tops, bottoms, and two side walls of endodermal cells in roots of plants.
  • Catabolic
    Degradative processes that generate energy for the cell through oxidation of organic molecules.
  • Catalyst
    A material that increases the rate of a chemical reaction without undergoing a chemical change.
  • Catalyzes
    Speeds up.
  • Cation
    A positively-charged ion.
  • Cation Exchange
    The interchange between a cation in solution and another cation at the surface of a negatively charged material such as clay or organic matter.
  • Cation Exchange Capacity (CEC)
    The ability of a soil to hold certain elements which have a positive charge; mainly a function of clay content and organic matter. Some plant nutrients, such as potassium and caldium are cations, so a soil with higher CEC will generally be more fertile because of its greater ability to hold these nutrients.  Measured in milliequivalents/100 grams.
  • Cation Exchange Capacity (CEC)
    The sum of exchangeable bases plus total soil acidity at a specific pH, values, usually 7.0 or 8.0. When acidity is expressed as salt extractable acidity, the cation exchange capacity is called the effective cation exchange capacity (ECEC) because this is considered to be the CEC of the exchanger at the native pH value. It is usually expressed in centimoles of charge per kilogram of exchanger (cmolckg-1) or millimoles of charge per kilogram of exchanger.
  • Cationic
    Having positive charge.
  • Cavitación
    La ocurrencia espontánea de una fase gaseosa en un líquido bajo tensión; ocurre en el xilema de las plantas que se encuentran bajo un estrés hídrico moderado a severo.
  • Cavitation
    Spontaneous occurrence of a vapor phase in a liquid under tension; occurs in xylem of plants that are under moderate to severe water-deficit stress.
  • Cavities
    Tunnels left inside the corn stalk from European corn borer feeding.
  • cDNA
    An abbreviation for complementary DNA; a DNA molecule made from an mRNA template that represents the entire coding region of the gene, but not the intron sequences.
  • Cell Membrane Disrupters
    Mode of action of a group of herbicides that kill by destroying cell integrity.
  • Cell Wall
    A thin, mechanically strong structure surrounding all plant cells consisting of a complex mixture of polysaccharides and other polymers that are secreted by the cell and are assembled into an organized network linked together by a mixture of covalent and noncovalent bonds. Cell walls regulate cell volume and determine cell shape.
  • Cellular Path
    Water moves from cell to cell using membranes, either across membranes or using plasmodesmata
  • Cellulose
    A polysaccharide of glucose units that constitutes the chief part of the cell walls of plants.
  • Celulosa
    Un polisacárido formado por unidades de glucosa que constituye el elemento fundamental de las paredes celulares en las plantas.
  • cement
    materials or substances which glue particles together
  • Centro de Reacción
    Un componente especializado dentro de un fotosistema encargado de efectuar las reacciones fotoquímicas utilizando la energía de excitación atrapada por los pigmentos antena.
  • Centromere
    The region of the chromosome associated with the attachment of the chromatids to the spindle fibers.
  • Certified Organic Foods
    Organic" is a labeling term that denotes products produced under the authority of the Organic Foods Production Act. The term "organic" details the methods, practices and substances that can be used in producing and handling organic crops and livestock, as well as processed products. Organic agriculture practices cannot ensure that products are completely free of residues, however methods are used to minimize pollution from air, soil, and water. For more information contact the USDA at
  • Channels
    A transport protein in the membrane of cells that are selective pores, through which molecules can diffuse across the membrane.
  • chi-square

    A statistical test used to measure if experimental data supports a particular hypothesis.

  • Chimeric Plant
    A transformed plant that has the new gene in only some of its cells.
  • Chisel
    A type of minimum tillage that breaks up the aggregates of the soil more than discing. A Chisel breaks up soil using closely spaced gangs of narrow shank-mounted tools (Glossary of Soil Science Terms). Depending on the types of chisel points attached, degreee of residue incorporation can vary.
  • Chisel
    A type of minimum tillage that breaks up the aggregates of the soil more than discing.
  • Chloroacetamides
    Family of herbicides that inhibit shoot inhibition and belong to the seedling growth inhibitor mode of action.
  • Chloroplast
    An organelle within the plant cell in which the photosynthetic reactions are compartmentalized. The thylakoid membranes within the chloroplast are the site of the photosynthetic pigments and electron transfer components used to make energy from photosynthesis. The non-membrane space within the chloroplast is called the stroma; this is where photosynthetic energy is used to convert CO2 into sugars.
  • Chloroplast
    The organelle in plant cells that contains chlorophyll and is the site of photosynthesis.
  • Chromatid
    One of the two side-by-side replicas of a chromosome produced through DNA replication during mitosis/meiosis.
  • Chromosome
    A unit of hereditary material composed of 1000's of genes. During cell division chromosomes duplicate and divide, maintaining the genetic integrity of the organism.
  • Chromosome
    A genetic structure in a cell composed of condensed DNA, which contains the genetic code for an organism.
  • Chromosome Map
    A genetic map showing the location of genes on a chromosome.
  • Citoplasma
    Un compartimiento que rodea al núcleo de las células tanto vegetales como animales y en el cual se encuentran suspendidos muchos organelos y moléculas.
  • Citosol
    La substancia líquida del protoplasma, excluyendo todos los organelos, tales como el núcleo, los plastidios y los ribosomas.
  • Clay
    A soil inorganic separate of less than 2 micrometers (< 0.002 mm.). This is smallest of the mineral soil separates.
  • Climate
    Precipitation, temperature and other aspects of climate affect how specific soils are formed.
  • Clonación del Gen
    Localización y copiado de un gen específico. Esta es la segunda etapa del proceso de ingeniería genética.
  • Clone
    Genetically identical cells or organisms all derived from a single ancestor by asexual or parasexual methods.
  • Cloned Gene
    A copy of a gene that has been combined with a plasmid and placed into a bacteria cell.
  • Cloning
    Asexually propagating an identical plant.
  • Cloroplasto
    Un organelo dentro de la célula vegetal en el cual se llevan a cabo las reacciones fotosintéticas. Las membranas del tilacoide dentro del cloroplasto son el sitio donde se localizan los pigmentos fotosintéticos y los componentes de los sistemas de transferencia de electrones necesarios para la síntesis de energía durante la fotosíntesis. El espacio que no forma parte de las membranas dentro del cloroplasto se denomina "estroma"; es ahí donde la energía fotosintética es utilizada para convertir el CO2 en carbohidratos.
  • Co-suppression
    The silencing of a gene do to introduction of a second copy of the gene.
  • Co-transforming
    Transforming a cell with two different genes at the same time.
  • CoA
    An abbreviation for coenzyme A; a molecule with an active thiol group that functions as an acyl or acetyl group carrier in several biochemical reactions.

  • Coding Region
    Region of the DNA sequence between the promoter and the termination sequence. It contains the instructions about how to make a specific protein.
  • Codominance
    The situation in which both alleles in a heterozygous organism are equally expressed resulting in a phenotype having characteristics from both alleles.
  • Codon
    Three consecutive nucleotides in an RNA molecule that code for a single amino acid.
  • Codon Bias
    The frequency with which individual codons are used by an organism.
  • Cofactor
    The nonprotein component of an enzyme. They often carry out activities for which amino acids are not suited.
  • Cohesion
    A molecular attraction of molecules.
  • Cohesive
    Able to stick together tightly.
  • Cohesivo
    Capaz de permanecer fuertemente unido.
  • Colchicine
    Alkaloid used to induce chromosome doubling in plant breeding; found in Colchicum autumnale (autumn crocus or meadow saffron).
  • Collar

    where the blade and leaf sheath meet on a grass plant.

  • colluvium
    materials or sediments transported downslope by gravity
  • Colonies
    Groups of identical cells (or bacteria) that develop from a single cell when the cell divides multiple times. The cells are considered 'clones' of the original cell.
  • Colony
    A group of identical cells (or bacteria) that develop from a single cell when the cell divides multiple times. The cells are considered 'clones' of the original cell.
  • Common Name
    The Common Name describes the chemical name of the active ingredient of the herbicide.
  • Community
    (Plant community). An assemblage of plants occurring together at any point in time, while denoting no particular ecological status. A unit of vegetation.
  • Compaction
    The process by which soil particles are rearranged to decrease void space and bring them into closer contact with one another, thereby increasing the bulk density.
  • Compartmentalize
    To separate with a barrier. This can mean a physical barrier such as a membrane, or two immiscible solvents such as oil and water
  • Competitive Inhibitor
    A molecule which has a similar structure as the normal substrate an enzyme acts upon. A competitive inhibitor inhibits an enzyme's activity by directly competing with the normal substrate in binding to the active site on the enzyme.
  • Complementary
    Term used in science to refer to the normal nucleotide-pairing in DNA replication, with cytosine pairing with guanine and adenine pairing with thymine.
  • Composite
    Member of the Asteraceae family.
  • Composite Flower
    A flower head resembling a single flower, but really composed of several florets inclosed in a common calyxlike involucre, as the sunflower or dandelion.
  • Compressibility
    The susceptibility of a soil to decrease in volume when subjected to load (pressure). 
  • Concentrated Superphosphate (0-46-0)
    A material manufactured by reacting phosphoric acid with finely ground rock phosphate; often used in bulk blended products.
  • Conducto
    Un canal a través del cual algo (por ejemplo, un fluido) es transportado.
  • Conduit
    A channel through which something (as a fluid) is conveyed.
  • Conjugated Double Bonds
    Double bonds on alternating pairs of carbon molecules in a linear or cyclic organic molecule. An example is as follows -C=C-C=C-C=C- The electrons in conjugated double bonds form a resonance structure that is smeared over the double bond system. These electrons are responsible for light absorption.
  • Conjugation
    Attachment of a molecule (herbicide) to another molecule like sugar, lipid, lingnin, cellulose, which inactivates the original molecule.
  • Conservation Tillage
    Any tillage sequence, the object of which is to minimize or reduce loss of soil and water; operationally, a tillage or tillage and planting combination which leaves a 30% or greater cover of crop residue on the surface.
  • Consistency
    The resistance of a soil to deformation or rupture.
  • Contact
    Process resulting in two objects (i.e. herbicide molecule and a plant) touching each other.
  • Contact Herbicide
    A herbicide that is not transiocated; the activity only occurs within the first few cells from the point of contact; an example would be paraquat; a "burner."
  • Contour
    The general form, structure, or shape of something, in this case the curvature shape of the land.
  • Control Point
    An enzymatic reaction that influences the flux through a pathway.
  • Conventional Tillage
    Primary and secondary tillage operations normally performed in preparing a seedbed and/or cultivating for a given crop grown in a given geographical area, usually resulting in <30% cover of crop residues remaining on the surface after completion of the tillage sequence.
  • Corms
    A thick, rounded underground stem that is modified into storage tissue, i.e., crocus, gladiolus.
  • Corn Belt
    An agricultural region of the central United States primarily in Iowa and Illinois, but also parts of Indiana, Minnesota, South Dakota, Nebraska, Kansas, Missouri, and Ohio.
  • Corolla
    The petals, collectively, as a unit.
  • Correlation
    The process of determining the relationship between plant nutrient uptake or yield and the amount of nutrient extracted by a particular soil test method.
  • Cortex
    The tissue in roots and stems lying between the epidermis and the vascular tissues.
  • Corymb

    More or less flat-topped, indeterminate inflorescence, the outer flowers open first.

    sketch of inflorescence showing outer flowers opening first and inner flowers still in bud

    Armitage, A.; Herbaceous Perennial Plants


  • Cotyledon
    The first leaf or leaves produced by the embryo of a flowering plant.
  • Cretaceous
    The last period of the Mesozoic, approximately 144 to 65 million years ago.

  • Critical Point
    The point at which soil test values delineate responsive soils (those where fertilizer additions increase yields) and nonresponsive soils.
  • Cross
    The deliberate mating of two parental types of organisms in genetic analysis.
  • Cross Breeding
    Breeding from a male and female of different lineage.
  • Cross-resistance
    Resistance within a plant to herbicides with the same site of action but from different herbicide families.
  • Cross-resistance
    The development of resistance of an European Corn Borer to a Bt protein as a result of resistance development to a different Bt protein even though the European Corn Borer may have never been exposed to the second protein.
  • Crossing
    The deliberate mating of two parental types of organisms in genetic analysis.
  • Crossover Events
    A crossover event is the exchange between two DNA molecules. The resultant DNA contains sequences (hence genes) not found in either parental DNA molecule. Each exchange is an event. Because the exchange occurs between strands of DNA, the genes are physically linked. The maxiumum number of crossover events between two genes is 50% (which is identical to independent assortment).
  • Cruzamiento
    El apareamiento deliberado de dos organismos progenitores en un estudio genético.
  • Cry Proteins
    Protein crystals produced naturally by Bacillus thuringiensis bacteria that are toxic to some insects. The gene that produces this protein can be inserted into the corn genome giving it European corn borer (ECB) resistance.
  • Crystalline Wax
    Crystalline looking wax occurring on leaf surfaces that is difficult to wet.
  • CTP
    (Chloroplast Transit Peptide): Specific amino acid sequences added to proteins which direct them to go to the chloroplast of the plant cell.
  • Cultivar

    Race or variety of a plant intentionally created or selected and maintained through cultivation.

  • Cultivo de Tejidos
    Células vegetales cultivadas in vitro, que pueden ser manipuladas y luego inducidas para desarrollar plantas completas.
  • Cuticle
    Waxy layer of material on the surface of the plant epidermis to help plants retain water and resist microbe invasion
  • Cutin

    A waxy transparent material in the cuticle of plants that contains highly polymerized esters of fatty acids.

  • Cutícula
    Capa cerosa que se encuentra sobre la epidermis de las plantas que ayuda a retener agua y resistir la invasión de microbios
  • Cyclohexanediones
    Family of herbicides that belong to the lipid synthesis inhibitor mode of action (dims).
  • Cymes

    More or less flat-topped, determinate inflorescence, the outer flowers open last.


    Armitage, A.;
    Herbaceous Perennial Plants

     More or less flat-topped, determinate inflorescence


  • Cysteine
    Nonessential amino acid (essential in infants and those with chronic diseases).
  • Cystenine
    Nonessential amino acid (essential in infants and those with chronic diseases).
  • Cytochrome P450
    Also known as cytochrome P-450 monooxygenases or CytP450s; multifunctional enzymes widely distributed among living organisms. They function as monooxygenases by binding and activating molecular oxygen, incorporating one of its atoms into an organic substrate, and reducing the second atom to form water.
  • Cytochrome P450
    A large family of mixed-function monooxygenases used for Phase I metabolism of xenobiotics in almost all eukaryotes.
  • Cytoplasm
    A compartment in a plant or animal cell surrounding the nucleus in which many cell organelles and molecules are suspended.
  • Cytoplasmic Cell
    The smaller, cytoplasm-rich cell from the cell division of a progenitor cell. Also called embryogenic cell. It will develop into either proembryonal complex or a somatic embryo.
  • Cytosol
    The liquid substance of protoplasm, excluding all the organelles such as nuclei, plastids, ribosomes.
  • Células Guarda
    Células epidérmicas especializadas que forman los bordes de los estomas, los poros en la superficie de las hojas de las plantas.
  • Células No Diferenciadas
    Células que no se han desarrollado a tejidos especializados. Las células no diferenciadas, llamadas callos, son usadas en cultivos de tejidos durante el proceso de transformación.
  • Córtex
    El tejido que se encuentra entre la epidermis y el sistema vascular de raíces y tallos.
  • De-differentiation
    The developmental process from a highly differentiated cell to an undifferentiated cell. It is a reverse to differentiation.
  • Decomposition
    Breakdown into constituent elements through chemical change.
  • Deficiency Correction
    One of three approaches to making fertilizer recommendations which is based on the concept that a nutrient should be applied only if there is a reasonable expectation of a crop response.  Under this approach, fertilizers should be applied only if they increase yields, and then only at optimum rates.
  • Defoliation

    cutting or removing leaf tissue.

  • Degradation
    The breakdown of a chemical by either chemical or physical reactions that make it inactive.
  • degrees of freedom

    In a chi-square analysis this is the number of classes in the data set minus one.

  • Denaturation Step
    The first temperature step in PCR. During this step, the DNA is made single-stranded, denatured.
  • Denature
    A process which breaks the H-bonds between DNA bases, making the molecule become single-stranded.
  • Denitrification
    NO3 ----> N2O and/or N2 Reduction of nitrogen oxides (usually nitrate and nitrite) to molecular nitrogen or nitrogen oxides with a lower oxidation state of nitrogen by bacterial activity (denitrification) or by chemical reactions involving nitrite (chemodenitrification). Nitrogen oxides are used by bacteria as terminal electron acceptors in place of oxygen in anaerobic or microaerophilic respiratory metabolism.
  • Denitrification
    The conversion of nitrate to various gaseous forms of nitrogen which can be lost to the atmosphere (nitric oxide, nitrous oxide, dinitrogen).  Denitrification occurs under oxygen-limiting conditions, such as when soils are saturated.
  • Deprotonated
    Dissociated; a molecule that has lost its proton due to a change in pH.
  • Detachment
    The removal of transportable fragments of soil material from a soil mass by an eroding agent, usually falling raindrops, running water, or wind; through detachment, soil particles or aggregates are made ready for transport.
  • Detoxication
    Altered so the compound is less toxic.
  • Diacylglycerol (DAG)
    A precursor in membrane lipid synthesis; diacylglycerol has two fatty acid groups attached to a glycerol back bone.
  • Diapause
    A type of hibernation that is a physiological condition resulting in suspended development of larva, such as ECB. It is controlled by day length, temperature, genetic composition of the insect and sometimes the nutritional quality of the host plant.
  • Dicots

    A subclass of of Angiosperms.

    They tend to have:
    -broad leaves
    -two cotyledons
    -netlike veins in the leaves
    -flower parts are usually in fours or fives
    -a ring of primary vascular bundles in the stem
    -taproot system

    ex. most trees and shrubs, broadleafs

  • Differentiation
    The developmental process that specializing cells' function and shape.
  • Diffusion
    Process whereby molecules move from areas of higher concentration to areas of lower concentration.
  • Dinitroanilines
    Family of herbicides that inhibit microtubule assembly and belong to the seedling growth inhibitor mode of action (DNA).
  • Diphenylether
    Family of herbicides belonging to the cell membrane disrupter mode of action.
  • Diploid
    Containing two sets of chromosomes; 2n.
  • Dipole
    A molecule or a functional group with a dipole moment.
  • Dipole Moment
    An electron asymmetry produces a local partial negative and partial charge. This separation of weak charge can be felt by the surrounding molecules. Fully charged functional groups (e.g. phosphate) also contain a dipole moment
  • Disc
    A type of minimum tillage that breaks up the organic matter and partially buries it in the soil. Depth of soil disturbance is seldom over 4-5 inches.
  • Disc Floret
    One of the individual small flowers that make up the central disc of a daisy flower (family Asteraceae), when these are different from the outer circle of longer-petalled ray florets, as in a sunflower.
  • Disociación
    Es la liberación de un protón (H+) de una molécula como consecuencia de un cambio de pH.
  • Dissociate
    (dissociation) – The splitting of a single chemical species into two ions, for example H2O to produce H+ and OH-.
  • Dissociation
    The release of a proton from a molecule due to a change in pH.
  • Division
    Asexual propagation of a plant by breaking the crown or suckers (must contain a node) to producte an identical plant.
  • DNA
    (deoxyribonucleic acid) The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. It is the fundamental substance of which genes are composed.
  • DNA Extraction
    The process of isolating the DNA from cells of an organism to allow scientists to work with and study it further.
  • DNA Markers
    DNA sequences that are found at specific loci in species that may vary in sequence among members of that species.
  • DNA Polymerase
    The enzyme which catalyzes the reaction of adding new DNA bases to a growing DNA strand.
  • DNA Replication
    The process in which a DNA molecule is copied. This takes place in PCR and naturally in cell division.
  • DNA Sequence
    The order of nucleotides, whether in a fragment of DNA, a gene, a chromosome, or an entire genome.
  • DNA Template
    That particular portion of a DNA molecule which is copied in PCR.
  • Domain
    A discrete portion of a protein with its own function. The combination of domains in a single protein determines its overall function.
  • Dominant
    The allele that is expressed in a heterozygous organism.
  • Donor Parent
    The parent from which one or a few genes are transferred to the recurrent parent in backcross breeding.
  • Dormancy
    In a condition of biological rest or inactivity characterized by cessation of growth or development and the suspension of many metabolic processes.
  • Double Helix
    The spiral shape that two linear strands of DNA assume when bonded together.
  • ds/M
    deciSiemens per meter, a measure of soil salinity equivalent to millimhos per centimeter (mmho/cm)
  • Dynamic
    Something that changes or moves; not static or stationary.
  • Ear Shank
    The part of the ear that is attached to the stalk of the corn plant. The ear shank is a transport for water and nutrients to the ear from the plant.
  • Efflux
    Movement from the cytoplasm to the cell wall region; out of the cell.
  • Electrochemical Potential
    Gradients of concentration and electric potential across cell membranes.
  • Electron Asymmetry
    The electrons that form a chemical bond between two atoms are not shared equally, resulting in one partner with a slightly negative charge (the tight sharer) and one partner with a slightly positive charge (the weaker sharer)
  • Electron Orbitals
    Electrons move about nuclei in spaces that have a characteristic shape. These orbiting shapes are called orbitals
  • Electron Transfer
    The transfer of electrons between a series of components in a controlled fashion. Examples include the mitochondrial electron transfer chain involved in oxidative phosphorylation and the chloroplast electron transfer chain carrying out photophosphorylation. Electrons are transferred from molecules with a higher free energy to those with a lower free energy.
  • Electrophilic Substrate
    A functional group that likes electrons; is seeking a negative charge.
  • Electrophoresis
    A technique which uses electricity to separate molecule fragments according to size so they can be studied.
  • Electrophoresis Buffer
    A solution of water and electrolytes that will conduct current for electrophoresis.
  • Electrophoresis Gel
    A gel matrix made from agarose, starch or acrylamide that is used to seperate large molecules such as proteins or DNA based on the rate they move with an electric current.
  • Electroporation
    A method of cell transformation using a pulse of electricity to open small temporary holes in the plant or bacteria cells. The foreign DNA mixed with these cells is able to pass into the cell through these holes.
  • Elemental Sulfur
    The most concentrated form of sulfur.  Elemental sulfur must be oxidized to the sulfate form before plants can use it.  It must be finely ground to particle sizes of 80-100 mesh to be oxidized and effective during the same growing season.
  • Elevated Meniscus
    A meniscus is formed when water interacts with the sides of a vessel or tube and does not form a flat surface. In an elevated meniscus, the water forms a rounded surface toward the air
  • ELISA (Enzyme-Linked ImmunoSorbent Assay)
    A test which can be used to detect the presence of proteins encoded by a specific gene.
  • Elite
    A crop line that has many genes for good agronomic traits that result in high yields in a particular environment.
  • Elite
    Una línea de cultivo que tiene muchos genes que le confieren características agronómicas excelentes, que resultan en un alto rendimiento en condiciones ambientales específicas.
  • Elite Experimental Line
    A line that is very close to release as a cultivar
  • Elongation Step
    The last temperatures step in PCR. During this step a DNA polymerase adds nucleotides to the growing DNA strand.
  • Emasculation
    Removal of the anthers/pollen of the flower.
  • Embryo
    The undeveloped plant in a seed.
  • Embryo Proper
    A cell mass that will develop into an embryo.
  • Emulsifier
    A surface-active agent promoting the formation and stabilization of an emulsion; promotes the mixing of two normally unmixable liquids; an emulsifier is used to didperse an oil within water.
  • Emulsion
    A system consisting of a liquid dispersed with an emulsifier in a second but immiscible liquid.
  • Endodermis
    The cells on the innermost cortex that form a barrier between the cortex and the vascular tissue in roots of plants
  • Endodermis
    Las células localizadas en el extremo interno del córtex, formando una barrera entre éste y el sistema vascular de las raíces
  • Endogenous
    Found naturally in an organism.
  • Endosymbiont Theory

    The theory that eukaryotic cells evolved from large prokaryotic cells that engulfed free-living bacteria; mitochondria evolved from aerobic bacteria and chloroplasts evolved from photosynthetic bacteria.

  • Endotoxin
    A protein that works internally as a toxin.
  • Energy of Activation
    The amount of kinetic energy required for conversion of a substrate to a product.
  • Enlace de Hidrógeno
    Una atracción electrostática entre un átomo de hidrógeno de una molécula polar de agua y un átomo electronegativo de oxígeno en otra molécula de agua.
  • Enlaces Dobles Conjugados
    Enlaces dobles en pares alternos de átomos de carbono, ya sea en una molécula orgánica linear o cíclica. Un ejemplo es el siguiente: C-C=C-C=C-C. Los electrones de los enlaces dobles conjugados forman una estructura de resonancia que es distribuida en el sistema de enlaces dobles. Esos electrones son los responsables de la absorción de la energía luminosa.
  • Enthalpy
    A measure of the total bond-energy (heat) in a molecule.
  • Entropy
    A measure of the degree of disorder in a system.
  • Environment
    The combinations of all the conditions external to the genome that potentially affect gene expression.
  • Enzima
    Una proteína que cataliza, o acelera, una reacción bioquímica específica sin cambiar la naturaleza de la reacción.
  • Enzimas
    Un tipo especial de proteínas que catalizan reacciones bioquímicas.
  • Enzyme
    A protein that catalyzes, or speeds up, a specific biochemical reaction without changing the nature of the reaction and without being changed in the the chemical reaction.
  • Ephemeral Gully Erosion
    See gully erosion.
  • Epinastia
    La curvatura hacia abajo que las hojas muestran cuando el lado superior del pecíolo crece más rápido que el lado inferior.
  • Epinasty
    The downward curvature of leaves that occurs when the upper side of the petiole grows faster than the lower side.
  • Epiphyseal Cells
    The meristem cells in epiphysis.
  • Epiphysis
    The shoot apical meristem tissue.
  • Epistasis
    Interaction between two loci, whereby the phenotypic effect of an allele at one locus depends on which allele is present at the other locus.
    5-enolpyruval-shikimate-3 phosphate syntheses; an enzyme essential for amino acid production that is the target site for glyphosate (Roundup).
  • erosion

     the wearing away of the land surface by wind or running water. 

  • ESR
    Electron spin resonance spectroscopy.
  • Essential Fatty Acids
    Fatty acids that are not synthesized by the human body, but are necessary for normal growth and life. These essential fatty acids are the linolenic and linoleic acids, and must be obtained from the diet.
  • Estado Triplete
    Un orbital electrónico en un estado excitado normalmente no permitido y el cual es reservado para un electrón con la misma dirección de giro a la del electrón que permanece en el estado basal. En ocasiones, un electrón que ha sido elevado a un estado excitado simple puede sufrir una inversión en la dirección de giro. Cuando esto sucede, ese electrón cae a un estado triplete, el cual posee menor energía que el estado simple. Una vez en el estado triplete, el electrón debe permanecer ahí hasta que su dirección de giro es nuevamente revertida. El oxígeno molecular (O2) es un caso inusual ya que es una molécula que normalmente se encuentra en un estado triplete.
  • Estados Simples
    Un orbital hacia el cual un electrón puede ser movido después de ser excitado por la energía de un fotón. Los orbitales en un estado simple requieren que el electrón excitado tenga una dirección giratoria opuesta a la del electrón que permanece en el estado basal.
  • Estoma
    Una apertura en la capa externa de células de una hoja, que está rodeada por dos células guardia y que sirve para el intercambio gaseoso.
  • Estomas
    Poros diminutos en la superficie de las hojas definidos por dos células guarda que posibilitan a los poros para abrirse y cerrarse en respuesta a cambios en las condiciones ambientales.
  • Ethidium Bromide
    Dye molecule with a structure that binds to DNA and will fluoresce under ultraviolet light.
  • Ethylene
    A plant hormone produced by most plant tissues involved in fruit ripening, seed germination, senescence, abscission, and other aspects of plant development.
  • Etileno
    Una fitohormona producida por la mayoría de los tejidos vegetales que está involucrada en la maduración de los frutos, germinación de la semilla, senescencia, abscisión y otros aspectos del desarrollo de la planta.
  • Eukaryotic Expression System
    A culture of yeast or baculovirus cells that, when transformed with a plasmid containing a cDNA, can express large quantities of the encoded protein.
  • European Corn Borer
    Ostrinia nubilalis (Hübner) is a major insect pest in corn that costs farmers millions of dollars annually in control expenditures and yield loss. The European corn borer (ECB) larva feed on the leaves and bore holes into the stalks where they tunnel.
  • European Corn Borer (ECB)
    Ostrinia nubilalis (Hübner) is a major insect pest in corn that costs farmers millions of dollars annually in control expenditures and yield loss. The European corn borer (ECB) larva feed on the leaves and bore holes into the stalks where they tunnel.
  • Euthrophication
    A condition in surface waters where high nutrient concentrations stimulate algal blooms which are sufficient to choke out some other forms of life. A more advanced state of nutrition pollution is a hypereutrophic condition where many clear water species cannot survive. Less contaminated states include oligiotrophic with clear waters and little biological activity and mesotrophic with an intermediate level of nutrient supply and biological activity.
  • Evaporación
    La conversión de un líquido a vapor.
  • Evaporation
    To convert from a liquid to a vapor.
  • Evapotranspiration
    The combined loss of water from a given area, and during a specific time, by evaporation from the soil surface and by transpiration from plants. (1997. Soil Science Society of America. p. 36)
  • Event
    The insertion of a particular transgene into a specific location on a chromosome. Events are differentiated by two factors: 1) what transgene was inserted, and 2) where on the chromosome it inserted and how many gene copies inserted at that locus.
  • Events
    The term used to differentiate different transgenic crops. Each event is the insertion of a particular transgene into a specific location on a chromosome. Events are differentiated by two factors: (1) what transgene was inserted, and (2) where on the chromosome it inserted and how many gene copies inserted at that locus.
  • Exogenous
    Applied externally; not from within the organism.
  • Exothermic
    Characterized by or formed with evolution of heat.
  • Exotérmico
    Caracterizado por, o formado con, producción de calor.
  • Expansins
    A special class of wall-loosening proteins which cause cell wall expansion by loosening the hydrogen bonding between wall polysaccharides.
  • expected

    When conducting a chi-square test, this is the number of individuals anticipated for a particular phenotypic class based upon ratios from a hypothesis.  An example would be an F2 3:1 ratio of yellow to green plants.   Expected numbers from 100 F2 plants would then be 75 yellow plants and 25 green plants.

  • Explants
    A piece of plant tissue cut for tissue culture.
  • Expressed Sequence Tags
    Short fragments of cDNAs that are used as markers or tags for expressed genes in genomic and mapping research.
  • Exserted
    Extends beyond the throat.
  • Extinción
    El proceso de desexcitación de una molécula de un estado excitado simple o triplete hacia el estado basal. El proceso de extinción de clorofilas excitadas es una importante función protectora de los carotenoides. Si una molécula en estado triplete no es rápidamente extinguida, ésta puede reaccionar con oxígeno molecular para generar oxígeno en estado simple. El oxígeno en estado simple puede causar mucho daño a nivel celular.
  • F1 Generation
    (first filial generation) The offspring produced from crossing two parental lines or individuals.
  • F2 Generation
    (second filial generation) The offspring produced from self crossing or intercrossing individuals in the F1 generation.
  • Fallow
    The practice of leaving land either uncropped and weed-free, or with volunteer vegetation during at least one period when a crop would normally be grown; objective may be to control weeds, accumulate water, and/or available plant nutrients.
  • Fatty Acids
    A class of compounds containing a long hydrocarbon chain and a terminal carboxyl group. Fatty acids can be saturated (containing no carbon-carbon double bond), monounsaturated (containing one carbon-carbon double bond), or polyunsaturated (containing multiple carbon-carbon double bonds).
  • Fauna
    Animal life.
  • Feedback Inhibition
    Type of enzymmatic regulation where the end product of a pathway regulates the enzyme's activity rate.
  • Ferritin
    Storage form of iron in the liver and other tissues.
  • Ferrous Sulfate
    The most commonly used inorganic iron source, which is 20 percent iron and 18.8 percent sulfur.  It is not effective as a soil-applied material because it quickly reverts to an unavailable form.
  • Fertigation
    Application of plant nutrients in irrigation water (1997. Soil Science Society of America. p. 38).
  • Fertile
    Bearing functional reproductive structures such as seeds, fruit, spores or pollen.
  • Fertilization
    The act or process of initiating biological reproduction by pollination.
  • Fertilizer Analysis
    The percent composition of a fertilizer as determined in a laboratory and expressed as total N, available phosphoric acid (P2O5) equivalent, and water-soluble potash (K2O) equivalent.
  • FI Hybrid
    The first generation of offspring produced by crossing two parents of different genotypes
  • Fibrous
    Composed of profusely branched roots with many lateral rootlets but with no main or tap root development.
    (Pest Management Glossary
  • Field Capacity
    Soil water content after the soil has been saturated and allowed to drain freely for 24 to 48 hours. Free drainage occurs because of the force of gravity pulling on the water. When water stops draining, we know that the remaining water is held in the soil with a force greater than that of gravity.
  • Field Water Capacity (FC)
    The content of water, on a mass or volume basis, remaining in a soil 2 or 3 days after having been wetted with water and after free drainage is negligible (1997. Soil Science Society of America. p. 40)
  • Filament
    The stalk that bears the anther in a stamen.
  • Fitotóxico
    Una substancia que es tóxica para las plantas.
  • Fixation, Nitrogen
    Conversion of molecular nitrogen (N2) to ammonia and subsequently to organic nitrogen utilizable in biological processes.
  • Flaccid
    Body becomes soft and weak, lacking firmness.
  • Flag leaf

    the top leaf on a stem.

  • Flanking
    Flanking means sequences that border something. Flanking primers are located on either side of a DNA sequence of interest.
  • Flash Grazing
    A relatively short grazing period usually involving high grazing pressure.
  • Flora
    Plant life.
  • Florets
    Small or reduced flowers; often found in grasses and the Asteraceae family.
  • Fluorescein
    A fluorescent dye.
  • Fluorescence
    Light emitted by an excited singlet molecule as part of the de-excitation process. Because a small amount of the energy in the original exciting photon is lost by molecular vibration before the emission of the fluorescence, the wavelength of fluorescence is greater (i.e. less energy) than the wavelength of the exciting photon.
  • Fluorescencia
    La luz emitida por una molécula en un estado excitado simple, como parte de un proceso de disipación de energía. Debido a que una pequeña cantidad de energía se pierde por vibración molecular antes de la emisión de la fluorescencia, la longitud de onda del fotón liberado es mayor (con menos energía) a la longitud de onda del fotón que llevó inicialmente al electrón al estado excitado simple.
  • Fluorophore
    A molecule which fluoresces, give off light energy, when excited by an external light source.
  • Foraging
    The search and consumption of forage.
  • Fosfatidilinositol
    Un lípido de la membrana del grupo de los fosfoinosítidos. Los fosfoinósitidos son fosfolípidos que contienen inositol que están involucrados en ligar señales extracelulares con respuestas intracelulares; es decir, con la traducción de señales.
  • Fosfoinosítidos
    Fosfolípidos que contienen inositol que están involucrados en conectar señales extracelulares con respuestas intracelulares; es decir, con la traducción de señales.
  • Fotofosforilación
    Un proceso de enlace entre los fotosistemas I y II con la cadena de transferencia de electrones que mueve los electrones del agua (la cual se oxida para formar O2) al NADP+ (el cual se reduce para formar NADPH). La transferencia de electrones entre el fotosistema I y el fotosistema II libera energía, la cual es conservada en la forma de un gradiente de protones a través de las membranas y utilizada para sintetizar ATP.
  • Fotosensibilizadores
    Moléculas que fácilmente pueden ser convertidos a un estado triplete después de la absorción de un fotón. Estas moléculas en un estado triplete pueden ya sea reducir otras moléculas para generar radicales libres, o bien pueden excitar al O2, que normalmente se encuentra en un estado triplete, para generar oxígeno en estado simple (1O2). Este último es altamente reactivo y puede causar daños celulares significativos.
  • Fotosistema
    Un arreglo de complejos pigmento-proteína y componentes de la transferencia de electrones que funcionan juntos para capturar energía luminosa, transferirla a los centros de reacción y mover los electrones excitados de una manera controlada para producir energía bioquímica útil. Cada fotosistema contiene cientos de moléculas de clorofila y carotenoides que funcionan como antena, mientras solo unas pocas moléculas de clorofila funcionan en los centros de reacción.
  • Fotosíntesis
    La conversión de la energía luminosa en energía química por las plantas usando compuestos inorgánicos de baja energía (bióxido de carbono) para producir compuestos orgánicos de alta energía (azúcares)
  • Fotón
    La unidad básica de la luz. Aunque posee las propiedades de una onda, la luz solar viaja en forma de paquetes de energía. Cada fotón es una partícula de radiación electromagnética que viaja a la velocidad de la luz (3 X 108 m sec-1). La energía de un fotón depende de la frecuencia a la que vibra su campo electromagnético.
  • Fragment Banding Pattern
    Bands made when many copies of the same DNA fragment move together through an electrophoresis gel. The pattern of bands reveals the the number of different size fragments in a sample.
  • Frecuencia
    Número de veces que el campo electromagnético de un fotón vibra por segundo.
  • Free Radical
    Any molecule with one unshared electron giving the molecule a partial negative charge; highly reactive and can cause permanent damage to cellular membranes.
  • Frequency

    A measure of the number of times per second (units of sec-1) that the electric field in a photon vibrates.

  • FRET
    Fluorescence Resonance Energy Transfer - a real time PCR DNA detection system, using flanking primers.
  • Fruit

    The ripened ovary or ovaries of a seed-bearing plant, together with accessory parts, containing the seeds and occurring in a wide variety of forms.

  • full cover

    when the crop fully shades the surrounding ground.

  • Functional Group

    an atom or group of atoms within a molecule that shows a characteristic set of physical and chemical properties.  For example, hydroxyl groups (-OH) are present in alcohols, carbonyl groups (-C=O) are present in ketones and aldehydes, and carboxyl groups (-COOH) are present in carboxylic acids.

  • Gamete
    A mature male or female reproductive cell (sperm or ovum) containing half of the total number of chromosomes in a cell (i.e., humans have 46 chromosomes per cell; gametes would have 23).
  • GC/MS
    Gas-liquid chromatograph coupled to a mass spectrometer
  • Gen
    La unidad básica de la herencia que transfiere la información genética de una generación a la siguiente. Un gen es una secuencia ordenada de nucleótidos que se localizan en una posición determinada de un cromosoma específico y que codifica la síntesis de una proteína en particular.
  • Gen Transformado
    Un gen que ha sido genéticamente alterado. Usualmente es utilizado para transformar organismos.
  • Gene
    The fundamental unit of heredity that carries genetic information from one generation to the next. A gene is an ordered sequence of nucleotides located on a particular position on a particular chromosome that encodes a specific functional protein.
  • Gene Action
    The phenotypic response observed when the dosage of an allele changes. For example, in the allelic series AA, AB, and BB, the dosage of the B allele changes from 0 to 1 to 2. Gene action may be additive (if AA<AB<BB), dominant (if AB=BB), or overdominant (if AB>BB).
  • Gene Cloning
    Finding and making copies of a specific gene. This is the first part of the genetic engineering process.
  • Gene Expression
    The production of a protein encoded by a gene. Gene expression is controlled by the promoter region of the gene.
  • Gene Flow
    Movement of genes among and between species or populations.
  • Gene Gun
    Also known as microprojectile bombardment and particle acceleration. The method used to transform cells using small gold or tungsten particles which are coated with DNA and literally shot into the cell.
  • Gene Library
    A collection of cloned DNA molecules representing all or part of an individual's genome.
  • Gene Mapping
    Determination of the relative positions of genes on a DNA molecule or chromosome and the distance between them.
  • Gene Silencing
    The inactivation of a gene by an organism to prevent the gene from expressing.
  • Gene Stacking
    Creating a plant with a desired combination of two or more unique genes. This can be done when the genes are first transferred into the cells by co-transformation, or during the breeding process by crossing two lines that each contain a different gene resulting in progeny with both genes.
  • Genetic Code
    The sequence of nucleotides, read three at a time, that determines the order of amino acids in a protein.
  • Genetic Engineering
    The process of adding foreign DNA to the genome of an organism.
  • Genetic Fingerprinting
    Determining the genetic makeup of an organism with the use of DNA markers.
  • Genetic Resistance

    genetically determined resistance to specified toxins/insecticides

  • Genetics
    The branch of biology that deals with heredity, especially the mechanisms of hereditary transmission and the variation of inherited characteristics among similar or related organisms.
  • Genoma
    Todo el material genético contenido en el paquete haploide de cromosomas de un organismo específico.
  • Genome
    All the genetic material in the haploid set of chromosomes for a particular organism.
  • Genotipo
    La composición alélica de una célula u organismo.
  • Genotype
    The allelic composition of a cell or organism.
  • Germ Line Cells
    Cells that give rise to gametes, the reproductive cells of an organism, (such as an egg or sperm), that have only one set of chromosomes. When the two unite, they form a living embryo.
  • Germination
    Process in which seeds or spores sprout and begin to grow.
  • Germline cells
    Cells that give rise to gametes, the reproductive cells of an organism, (such as an egg or sperm), that have only one set of chromosomes. When the two unite, they form a living embryo.
  • Germplasm
    The total of the inherited materials, or genes, in a species.
  • Glifosato
    Un herbicida que inhibe la producción de ciertos aminoácidos en la planta.
  • Globular Stage
    The developmental stage of embryogenesis that the embryonic tissues organized as a ball.
  • Glutathione
    A tripeptide made from glutamic acid, cysteine, and glycine used as the major anti-oxidant molecule in cells for binding and detoxifying many xenobiotics.
  • Glutathione Transferase
    An enzyme that catalyzes the binding of xenobiotics to glutathione.
  • Glycerolipids
    The family of lipids containing a glycerol backbone.
  • Glyphosate
    A herbicide which inhibits the production of amino acids.
  • goodness of fit

    A statistical term which refers to how well numbers of what was expected and numbers of what is observed are the same.  How well does your experimental data fit or support your hypothesis?

  • Graminicide
    Herbicides that target the grass family (Graminae); refers to the lipid synthesis inhibitor herbicides that or only effective on grasses.
  • Grandular Hair
    A hair with a minute bead of clear liquid at its apex.
  • Grassed Waterway
    A natural or constructed waterway, usually broad and shallow, covered with grasses, used to conduct surface water from or through cropland.
  • Grassland
    Land on which the vegetation is dominated by grasses, grasslike plants, and/or forbs. Herbaceous vegetation provides at least 80% of the canopy cover.
  • Gravitational Water
    The amount of water held by the soil between saturation and field capacity.
  • Grazing Capacity
    The optimal stocking rate that will achieve a target level of animal performance (e.g., average daily gain) or other specific objective, while preventing deterioration of the ecosystem.
  • Grazing Distribution
    Dispersion of animals during grazing within a management unit or area.
  • Grazing Efficiency
    The percentage of the total standing crop by weight that is ingested.
  • Grazing Pressure
    Animal demand per unit weight of forage dry matter either at an instant in time (AU/T) or over a period of time (AUM/T).
  • greenhouse effect
    infrared radiation absorbed by the atmosphere that is then emitted back to earth, warming the earth. This effect can be significant if the atmosphere is enriched with greenhouse gases such as carbon dioxide, methane, nitrous oxide gases.

  • Ground Miristem
    The primary embryonic tissues that surround the plant stem and branches.
  • Growing point

    a point on the plant where cells are capable of producing new plant tissues.

  • Growth Regulators
    Mode of action of herbicides that mimic plant hormones causing unregulated growth.
  • Guard Cells
    Specialized epidermal cells that form the boundaries of stomata, the pores in plant leaf surfaces.
  • Gully
    A channel resulting from erosion and caused by the concentrated but intermittent flow of water usually during and immediately following heavy rains. Deep enough (usually >0.5 m) to interfere with, and not to be obliterated by, normal tillage operations.
  • Gully Erosion
    The erosion process whereby water accumulates and often recurs in narrow channels and, over short periods, removes soil from this narrow area to considerable depths, often defined for agricultural land in terms of channels too deep to easily ameliorate with ordinary farm tillage equipment, typically ranging from 0.5m to as much as 25 to 30 m.
  • Gynoecium

    The female reproductive organs of a flower; the pistil or pistils considered as a group.

  • H+-ATPase
    a membrane protein located in the plasma membrane and tonoplast, used to carry out primary active transport of H+ out of the cytosol by coupling directly to the energy released during ATP hydrolysis
  • Half-Life
    The time it takes for a compound to degrade to half of its original concentration.
  • Halophytic
    Having characteristics of salt tolerance.
  • Head
    The inflorescence (composite), consisting of ray and disc flowers:  Gaillardia, sunflower, coneflower, plants of the Asteraceae (composite) family.
  • Heart Stage
    A developmental stage in embryogenesis that the young embryo looks like a heart.  At this stage, most all organs in a young plant have been formed.
  • Heat Shock
    A method of cell transformation that opens small temporary holes in the plant cell wall by alternating temperatures between hot and cold. Foreign DNA mixed with these cells is able to pass into the cell through these holes.
  • Hemizygous
    An organism that has a gene copy in only one chromosome in a chromosome pair (i.e., during the transformation process, the transgene will insert into only one chromosome of a pair).
  • Henry's Law
    The moles of a particular gas that can be dissolved into a solvent depends on the partial pressure of that gas in the atmosphere.
  • Herbaceous
    A characteristic that distinguishes a herb from a woody; no persistant, woody tissue above ground.
  • Herbicida
    Un pesticida usado para matar plantas.
  • Herbicida Auxínico
    Los primeros herbicidas orgánicos selectivos desarrollados. Esta familia de herbicidas es descrito como auxinas sintéticas, reguladores del crecimiento con acción herbicida o herbicidas con actividad reguladora del crecimiento.
  • Herbicide
    A pesticide used to kill plants.
  • Herbicide Family
    A group of herbicides that have similar chemical structure and kill plants by the same mechanism of action.
  • Herbicide Resistance
    The inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type. In a plant, resistance may be naturally occurring or induced by such techniques as genetic engineering or selection of variants produced by tissue culture or mutagenesis.
  • Herbicide safeners
    Chemicals that protect crops from injury by herbicides, but do not prevent the herbicide from killing weeds.
  • Herbicide Tolerance
    The inherent ability of a species to survive and reproduce after herbicide treatment. This implies that there was no selection or genetic manipulation to make the plant tolerant; it is naturally tolerant.
  • Hereditable
    Capable of being passed from one generation to the next; hereditary.
  • Heritability
    The proportion of phenotypic variation that is due to genetics, as opposed to environment or genotype x environment interaction.
  • Heterologous Genes
    A gene transferred from another organism which expresses the same trait as an endogenous gene.
  • Heterozygote
    An organism having two different alleles at one or more locations.
  • Heterozygous
    An organism that has two different alleles at one or more locations on a chromosome.
  • Hexane
    A organic molecule that forms a nonpolar solvent [CH3(CH2)4CH3].
  • Hidrofóbico
    ATemor al agua@; compuestos que son relativamente insolubles en agua y otros solventes polares pero solubles en lípidos y otros solventes no polares.
  • Homeothermy
    Refers to body temperature that is constant and largely independent of the temperature of the animal’s surroundings.
  • Homologous
    Having the same function, structure, position or value.
  • Homozygosity
    Having like alleles at corresponding loci on homologous chromosomes.  An organism can be homozygous at on, several, or all loci.
  • Homozygote
    An organism having identical alleles at one or more locations.
  • Homozygous
    An organism that has two identical alleles at one or more locations on a chromosome. Inbred lines are homozygous at many of their gene loci.
  • Horizons, Soil
    The layers of soil, usually three, which make up the soil profile. Soil horizons differ in color, texture, structure and organic matter content. The A Horizon is the upper surface or topsoil and usually has the highest organic matter content; the B Horizon is the subsoil; and the C Horizon is the parent material. A given soil may have one or all three horizons.
  • Hormones
    A chemical substance produced in a part of a plant that initiates and controls growth and flowering in another part of the plant.
  • horsepower

    the standard measure of power; power is the rate at which work is accomplished, or work divided by time (ft-lb/min).

    High performance liquid chromatograph coupled to a mass spectrometer.
  • HR
    Humedad relativa.
  • Humedad Relativa
    La proporción entre el vapor de agua existente en el aire y la cantidad máxima de agua que a la misma temperatura podría potencialmente retenerse en ese aire.
  • humus
    The well decomposed, more or less stable part of the organic matter in mineral soils
  • Humus
    An organic material in soil which is a product of plant and animal remains that have decomposed and then synthesized into something new.
  • Hybrid
    An individual produced by crossing two parents of different genotypes.
  • Hybrids
    Individuals produced by crossing two parents of different genotypes.
  • Hydrocarbon
    A compound that contains only C-C and C-H bonds (i.e. CxHy).
  • Hydrogen Bonding
    An electrostatic attraction between a hydrogen atom in one polar molecule of water and a small electronegative atom (oxygen) in another molecule of water.
  • Hydrolysis
    (Hydrolyze) – A chemical reaction in which some reactant combines with water and splits the water into hydrogen and hydroxyl ions.
  • Hydrolyze
    A chemical reaction in which some reactant combines with water and splits the water into hydrogen and hydroxyl ions.
  • Hydrophilic
    Having chemical properties relating to water (water-like).  Compounds are polar or ionizable and can be soluble in water; lipophobic.
  • Hydrophobic
    Water "fearing"; compounds that are relatively insoluble in water and other polar solvents and soluble in lipids and other nonpolar solvents.
  • Hydroseeding
    A process of spray grass-seeding with a mixture or blend of cellulose fiber mulch, grass seed and water.  This forms a mat or blanket on the soil to enhance seed germination, vigorous growth, and good rooting system.  Also known as "hydromulching."
  • Hydrostatic Pressure
    The positive pressure built up when water is compressed.
  • Hyperhydricity
    A network formed by hydroxyl connection.
  • Hypertrophy
    Excessive development of an organ or part; exaggerated growth or complexity.
  • Hypophyseal Region
    The tissue of a developing embryo that is derived from the topmost cell of the suspensor and is later incorporated into the root apex of the embryo, giving rise to part of the root cap, its initial cells and the ground meristem initial cells.
  • Hypoxia
    Oxygen deficiency in bodies of water created by pollution from nutrients and sediments.
  • Híbridos
    Individuos producidos mediante el cruzamiento de progenitores de diferente genotipo.
  • Imidazolinones
    A family of herbicides that are similar in chemical structure (imidazolinone ring) and have the same mechanism of action - amino acid synthesis inhibition.
  • Immiscible
    Two solvents that are not able to dissolve into each other when mixed.
  • Immobilization
    The conversion of an element from the inorganic to the organic form in microbial tissues, so that the element is not readily available to other organisms.
  • In Vitro
    In an experimental situation outside the organism (literally, "in glass").
  • In Vivo
    In a living cell or organism.
  • Inactivate
    The process of making a herbicide nonherbicidal by degradation or bonding to another molecule.
  • Inbred
    An organism that has been self-fertilized for several generations until it is homozygous at all important gene loci, "genetically pure."
  • Inbreeding
    Mating between closely related organisms.
  • Incomplete Dominance
    Expression of a heterozygous phenotype which is different from, and often intermediate to, that of either homozygous parent.
  • Indehiscent

    Not opening to release seeds when maturity is reached.

  • Indeterminate

    Center flowers open last in an inflorescence; the growth of the plant's main axis is not stopped with the opening of the first buds.

  • Inducing Medium
    The tissue culture media for helping the start of organ or embryonic cell development.
  • Infiltration
    Penetration of water into and through soil pore spaces. How much water penetrates depends on several factors, including the rate of precipitation, soil moisture condition and soil texture.
  • Infiltration, Water
    Water movement in the soil.  Pore space in soil is the conduit that allows water to infiltrate and percolate (downward movement of water through the soil).
  • Inflorescence
    The arrangement of flowers on a stem; inflorescence types include corymb, cyme, head, panicle, solitary, raceme, spike thyrse, and umbel.
  • Inflorescence
    A characteristic arrangement of flowers in a cluster on a stem.
  • Influx
    Movement from the cell wall region into the cytoplasm; into of the cell.
  • Ingeniería Genética
    El proceso por el que se transfiere ADN ajeno al genoma de un organismo.
  • Inhibidor Competitivo
    Una molécula con estructura química similar a la del substrato que normalmente es utilizado por una enzima. Esta molécula inhibe la actividad enzimática al competir directamente con el substrato por ocupar los sitios activos de la enzima.
  • Insoluble
    This occurs when molecules in a solid material are put into a solvent and are unable to leave the solid and enter the solvent.
  • Intense Selection
    Selection for the trait(s) of interest with little or no retention of lines not having the trait(s) of interest.
  • Intercalating Dye
    A dye molecule which can insert between bases of DNA. Used in laboratories to detect DNA sequences.
  • Intercalation
    When a molecule, such as Ethidium Bromide or SYBR Green inserts in between DNA nucleotides of a double-stranded DNA moledule. Ethidium Bromide and SYBR Green are therefore, used in detecting the presence of DNA.
  • Internode

    the space on the stem between nodes.

  • Interphase
    The stage of cell division when DNA is replicated; a copy of each chromosome is made.
  • Interspecific
    Arising or occurring between species.
  • Intraspecific
    Arising or occurring within a species.
  • Intron
    A portion of DNA located between coding regions in a gene which is transcribed, but spliced out of the mRNA before translation. This region of nucleotides does not actually code for any proteins.
  • Involucral Bracts
    A series of bracts beneath or around a flower or cluster of flowers.
  • Ion Trap
    When a the acid form of a weak acid (HA) enters the alkaline cytoplasm, it dissociates into its conjugate base (A-) but cannot escape back across the membrane because of its hydrophilic nature.
  • Ions
    Molecules with a positive or negative charge.
  • Iron Oxides
    Group name for the oxides and hydroxides of iron. Includes the minerals goethite, hematite, lepidocrocite, ferrihydrite, maghemite, and magnetite. Sometimes referred to as "sesquioxides," or "iron hydrous oxides."
  • Isoprenoids
    Also known as terpenes, this is a diverse class of biomolecules. They have in common a five carbon branched molecule as the basic building block.
  • Isozyme
    An enzyme that is similar in structure and function to another enzyme.
  • Karyotype
    A photograph of an individual's chromosomes arranged in order showing the number, size, and shape of each individual chromosome.
  • Kcat
    The number of reactions per second that the enzyme can catalyze under optimum conditions.
  • Key Management Species
    Plant species on which management of a specific unit is based.
  • Km
    The Michaelis constant. It is an indication of the affinity of the enzyme for the substrate.
  • Knockout Genes
    Transgenes designed to silence an existing gene.
  • Kow

    Octanol/water partition coefficient; relative measurement of how water soluble a chemical is; a compound with a low Kow would be more water-soluble than a compound with a high Kow.

  • Labile Phosphorus
    Intermediate form of phosphorus that is rather weakly adsorbed or bound to various compounds and clay in the soil.
  • lacustrine
    deposits of lake materials

  • Larva
    Newly hatched, wingless, worm-like stage of an insect.
  • Lateral Flow Strip
    A variation on the ELISA tests, using strips as opposed to microtiter wells to detect the presence of a protein produced.
  • Lateral Moraines
    An accumulation of soil, pebbles, rocks, and boulders distributed and marking the lateral edges of a glacier or ice sheet.
  • lava
    molten rock expelled from the earth during a volcanic eruption.
  • Layering
    Asexual propagation of a plant that has roots develop on a shoot before it is detached from the parent plant.
  • LD50
    The dose of chemical that can kill 50% of the test subjects.
  • Leaching
    The removal of soluble materials from one zone in soil to another via water movement in the profile. (Soil Science Society of America. 1997, p. 62).
  • leaf area index (LAI)

    the ratio of the leaf surface area (one side of the leaf) to land surface area. For example, if there is an average of 15 square feet of leaf surface for each 5 square feet of land surface, then the LAI is 3.0.

  • Ligase
    An enzyme that can rejoin cut strand of DNA.
  • Lignin
    The complex phenolic polymer that endows the xylem and other tissues in plants with compression and decay resistance.
  • Lignina
    El complejo polímero fenólico que suministra al xilema y otros tejidos fuerza de compresión y resistencia a la degradación.
  • Lime
    A naturally occurring material composed of carbonates of calcium and magnesium.
  • Line
    Plants within a species that have the same genetic composition and are genetically pure, (i.e., inbred line). Lines are typically not agronomically competitive and are used only in plant breeding.
  • Linkage
    The association of genes on the same chromosome. The shorter the distance between two genes, the greater the probability they will be inherited together.
  • Linkage Disequilibrium
    The condition whereby alleles at two loci occur together in a population at a greater frequency than that predicted by the product of the individual allele frequencies.
  • Linkage Map
    An ordered representation of genes on a chromosome derived from observed percentages of recombination. Units on a linkage map are centiMorgans (cM), with 1 cM approximately equal to 1% recombination.
  • Linkage Drag
    The inheritance of undesirable genes along with a beneficial gene due to their close linkage.
  • Lipid Bilayer
    Made up of compounds which have both hydrophobic and hydrophilic moieties, this is the structure of membranes such as the cellular membrane.
  • Lipid Synthesis Inhibitors
    Mode of action of herbicides that target the production of lipids which are essential in plant growth and function.
  • Lipids
    A structurally diverse group of hydrophobic compounds that are soluble in organic solvents and highly insoluble in water.
  • Lipophilic
    Having chemical properties relating to lipids (lipid-like), nonpolar compounds that are highly soluble in organic solvents, but not water; hydrophobic.
  • Locus
    The site on a chromosome where a particular gene (or other sequence) is located (plural=loci).
  • LOD
    Abbreviation for logarithm of odds, a significance measure used in maximum likelihood statistics. In interval mapping, the LOD score is log10 of the ratio of the probability that a QTL is present to the probability that a QTL is absent. For example, if the presence of a QTL is 1000 times more probable than its absence, then the LOD score = 3, because log10 of 1000 = 3.
  • Lodged
    Occurs when plant stalks (such as corn plants) have been damaged by insect, disease, or climate which results in the plant falling over.
  • Loess
    Material transported and deposited by wind and consisting of predominantly silt-sized particles. (SSSA)
  • Log Kow
    Octanol/water partition coefficient, relative measurement of how water soluble a chemical is. A compound with a low log Kow would be more water-soluble than a compound with a high log Kow.
  • Longitud de Onda
    La distancia que existe entre dos posiciones equivalentes contiguas (por ejemplo entre dos crestas) en el campo electromagnético formado por un fotón conforme viaja en el espacio. En el espectro visible, la longitud de onda de los fotones varía entre los 400 y los 700 nm.
  • Loss-of-function mutants
    Biotypes that have lost the ability to carry out a particular enzymatic reaction.

  • Lysine
    Nonessential amino acid found in cheese, eggs, milk, meat, legumes, whole grains, and nuts.
  • Lysis
    The dissolution or destruction of cells by the disruption of the cell membrane.
  • Línea
    Plantas dentro de una especie que tienen la misma composición genética y son genéticamente puras (es decir, líneas congénitas). Típicamente, las líneas no son agronómicamente competitivas y son usadas solo con propósitos de fitomejoramiento.
  • Macromolecules
    Large molecules which are composed of smaller individual molecules.
  • Macronutrients
    Elements needed in relatively large amounts for plant growth. Macronutrients include carbon, hydrogen, sulfur, nitrogen, phosphorus, potassium, calcium, magnesium, and oxygen.
  • magma
    molten rock located deep beneath the surface of the earth
  • magma chamber
    pool or collection of molten rock or magma beneath the surface of the earth

  • Maintenance Approach
    One of three approaches to making fertilizer recommendations which sets soil test level goals for specific nutrients and then recommends fertilizer to build the soil to those nutrient goals.  The maintenance approach emphasizes maintaining the soil fertility level at or above the point of the economic maximum yield.
  • Male Sterile
    Plant that does not produce viable pollen.
  • Malonylation
    Conjugation of a glucose conjugate of xenobiotic to malonyl in the presence of malonyl-CoA and malonyl-CoA-transferase; considered a Phase III reaction or secondary conjugation.
  • Marker
    An easy to detect trait controlled by a known gene. Markers, such as antibiotic or herbicide resistance, are often used to determine if an organism is transgenic.
  • Marker Gene
    A gene controlling an easily detectable trait used to select transgenic cells or plants from non-transgenic ones, (i.e., herbicide and antibiotic resistance).
  • Mass Flow
    Process by which a dissolved or suspended molecule is moved with movement of the solvent, i.e., a floating piece of wood moving with the current in a stream.
  • Mass Wasting
    Movement of disintegrated rock materials by sliding or falling to the base of a slope by the force of gravity.
  • Master Horizon
    A principal horizon, such as the A, E, B, C, or R.
  • Maximum Contaminant Limit (MCL)
    The highest level of a contaminant that is allowed in drinking water.
  • Maíz Bt
    Maíz que ha sido transformado con el gen Bt y que es resistente al barrenador Europeo del maíz.
  • Mechanical Analysis
    The laboratory procedure used to identify soil separates.
  • Mechanism of Action
    The specific process inhibited by a herbicide.
  • Mehlich 3
    Chemical extraction method developed by A. Mehlich in 1984 to estimate the availability of P to plants.
  • Meiosis
    A type of cell division which results in the formation of gametes, cells with half the normal number of chromosomes.
  • melt
    rock liquified by temperature and pressure
  • Membrana Plasmática
    La membrana semipermeable que rodea al protoplasma de una célula.
  • Mensajeros Secundarios
    Señales secundarias transitorias dentro de la célula que amplifican de manera significativa la señal original.
  • Meristems
    Area of cell division.
  • Metabolic Inhibitor
    An agent that decreases the velocity of an enzyme-catalyzed reaction.
  • Metabolism
    The sum of all chemcial processess occurring within a cell or an organism.
  • Metabolism
    A general term referring to the change of a herbicide from an active to an inactive state.
  • Metabolismo
    Alteración de la estructura química de un herbicida en la planta que usualmente elimina su toxicidad. El metabolismo es el mecanismo más importante de selectividad entre malezas y cultivos.
  • Metabolizing

    The sum of all chemical processes occurring within a cell or an organism.

  • Methionine
    An essential amino acid found in cereal, whole grains, sesame and sunflower seeds, and yeast.
  • Microarray
    A small glass, or filter, square containing probes for thousands of gene products.
  • microbes
    microscopic organisms such as bacteria and fungi
  • Microfibers
    A method used to transform tissue culture cells using tiny fibers coated with DNA. These fibers are combined in solution with the cells and shaken vigorously causing the fibers to stab the plant cells delivering the DNA to them.
  • Microfibrillas
    En las células guarda, las microfibrillas están formadas de celulosa y están orientadas transversalmente con relación al eje más largo de las células, dando como resultado una expansión de las células en la dirección del eje largo debido a que el refuerzo de celulosa ofrece la menor resistencia en los ángulos rectos de su orientación.
  • Microfibrils
    In guard cells, microfibrils are made of cellulose and are oriented transversely to the long axis of the cell resulting in cell expansion in the direction of its long axis because the cellulose reinforcement offers the least resistance at right angles to its orientation.
  • Microfiltration
    Removes particles, such as microorganisms and macro-molecules, from solution by passing it through a micro-filter.
  • Micronutrients
    Elements needed in very small amounts for plant growth.  Micronutrients include zinc, iron, chlorine, copper, manganese, boron and molybdenum.
  • Micropropagation
    Tissue culture technique that asexually propagates a clone of a plant from tissue.
  • Microtiter Plates
    Plastic plates containing many (96 to 864) small wells in which individual reactions or assays can be conducted; their format is designed for robotic manipulators and detectors.
  • Midvein
    Runs down the center of the leaf blade; is part of the framework of the leaf and gives support.
  • Mineralization
    The conversion of an element from an organic form to an inorganic state as a result of microbial activity.
  • Mineralized
    The conversion of an element from an organic form to an inorganic state as a result of microbial activity.
  • Mineralizes
    The conversion of an element from an organic form to an inorganic state as a result of microbial activity.
  • Miscible
    Two solvents that are able to dissolve into each other when mixed.
  • Mitigation
    Correction of a problem, often due to the presence of a pollutant.
  • Mixed-Function Oxidase
    Enzymes that catalyze oxidation of several substrates.
  • Modes of Action
    The method by which an organism is affected, damaged or killed. The mode of action usually involves a chemical reaction instigated by another source. (herbicide, etc.).
  • Modo de Acción
    Mecanismo por medio del cual un herbicida afecta el crecimiento y/o desarrollo de una planta. Esto incluye la absorción, el transporte y los efectos generales sobre la planta.
  • Molecular Marker
    An identifiable DNA sequence on a chromosome. A marker can be a gene, part of a gene, or a sequence in a non-gene region. SSR, RFLP, RAPD, and AFLP are acronyms for commonly used marker techniques.
  • Monoecious

    Having separate male and female organs or flowers on a single plant, as in corn and pines.

  • Monopolar
    Develop or move toward one direction.
  • Morphogenesis
    The process of morphology development.
  • Morphology
    The study of the form and structure of an organism.
  • Most Limiting Nutrient
    Justus von Liebig formulated the law of the minimum: plant growth is limited by the most deficient nutrient, even if the other elements are abundant.
  • mRNA
    (messenger ribonucleic acid) The message made during transcription by reading the DNA sequence to build a particular protein. A single-stranded nucleic acid similar to DNA but having a ribose sugar rather than deoxyribose sugar and a uracil rather than thymine as one of the bases.
  • MS Medium
    A popular plant tissue culture medium developed by T. Murashige and F. Skoog.
  • Multiple Resistance
    Evolution of populations resistant to herbicides not chemically related and having different sites of action, such as a weed resistant to both sulfonylurea and aryl-.
  • Mutation
    Any change in a DNA sequence.
  • Mutation

    A change of the DNA sequence within a gene or chromosome of an organism resulting in the creation of a new character or trait not found in the parental type.

    Reduced nicotinic adenine dinucleotide phosphate
  • Negative Cross Resistance
    Occurs when a resistant biotype is more susceptible to other classes of herbicides than the susceptible biotype.
  • Nitrate
    One of the mineral forms of nitrogen (NO3-).
  • Nitrification
    The conversion of ammonium to nitrate by bacteria in soil (NH4 ----> NO3).
  • Nitrification Inhibitor
    A chemical which, when applied to the soil, slows or temporarily prevents the biological oxidation of ammonium to nitrite and nitrate.
  • Nitrogen

    An essential chemical element for biological life.

  • Nitrogen Cycle
    The transitional process taking nitrogen from its simplest stable form (dinitrogen) and following it through fixation, mineralization, nitrification, leaching, plant assimilation, ammonia volatilization, denitrification and immobilization.
  • Nitrogen Fixation
    The process of converting dinitrogen gas to chemically reactive forms, where nitrogen combines with other elements, such as oxygen, hydrogen and carbon.
  • Nitrogen Gas
    The most abundant form of nitrogen existing as a gas, making up the bulk of the gas in the air (~78%). N2
  • Nitrogen-Phosphorus-Potassium Fertilizers
    Fertilizers manufactured using ammonium phosphate, to which potassium (usually potassium chloride) and water have been added; additional nitrogen and other nutrients also may be added.
  • Nitrous Oxide
    One of the gaseous form of mineral nitrogen. N2O
  • NMR
    Nuclear magnetic resonance spectrometry.
  • No-Till
    Lack of any tillage at all. The soil is not broken except for planting and maybe for some fertilization.
  • Nodes
    A joint on a stem where shoots, leaves and flowers arise.
  • Non-Labile Phosphorus
    A slowly available form of phosphorus.
  • non-point source pollution

    contamination for which there is no single, identifiable source; in agriculture, likely to have come from an entire field, farm, or an entire farming area.

  • Non-Polar
    A molecule with functional groups lacking dipole moments (e.g. alkyls and aryls).
  • Non-Polar Functional Groups
    Functional groups generally containing C and H atoms that do not form dipole moments.
  • Non-Polar Solvent
    A solvent with functional groups lacking dipole moments (e.g. alkyls and aryls).
  • Nonlimiting Water Range
    The region bounded by the upper and lower soil water content over which water oxygen and mechanical resistance are not limiting to plant growth (1997. Soil Science Society of America. p. 71).
  • Nontarget Genes
    Genes in the recurrent parent that are not at the locus of the gene of interest. Basically, nontarget genes are all those genes in the recurrent parent that the backcross breeder would like to retain in the backcrossing program.
  • Normal
    Frequency distribution whose plot is bell-shaped and symmetrical.
  • Normal
    Conforming with, adhering to, or constituting a norm, standard, pattern, level, or type; typical.
  • Northern
    A Method used to transfer RNA molecules separated during electrophoresis to membrane filters for detection of specific nucleotide sequences using probes.
  • Nucleophile
    Seeks positive charge; may be negatively charged or neutral.
  • Nucleotide
    A subunit of DNA or RNA consisting of a nitrogenous base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate molecule, and a sugar molecule. Thousands of nucleotides are linked together to form a DNA strand.
  • Nucleotides
    The building blocks of DNA and RNA; adenine, cytosine, guanine, thymine (DNA only), and uracil (RNA only).
  • Nucleus
    The part of the plant or animal cell that contains the chromosomes.
  • Nutrient Removal
    One of three approaches to making fertilizer recommendations, nutrient removal is the oldest method and was developed before reliable soil testing was readily available.   Under this approach, fertilizer recommendations are based on how much nutrient a specific crop is likely to remove from the soil and how much nutrient will be needed to replace it.  It does not account for soils’ ability to supply many essential nutrients.
  • Núcleo
    La parte de una célula animal o vegetal que contiene a los cromosomas.
  • O Line

    A structure in young embryo which is the lower boundary of shoot apical tissues.

  • observed

    When conducting a chi-square test, this is the number of individuals seen for a particular phenotypic class, ie. 78 yellow plants, 22 green plants.

  • obsidian
    an extrusive igneous rock that formed without sufficient time for crystal formation
  • Offset
    A young plant produced at the base of a parent plant.
  • OH

    A germplasm developed/improved at the Ohio State University.

  • Oil Additives
    An additive made either synthetically or extracted from seeds that enhances herbicide uptake into the plant; crop oils, methylated seed oils, crop oil concentrates.
  • Oligonucleotide
    Small fragments of nucleotides hooked together; primers used in PCR.
  • Oligonucleotide Libraries
    Collections of many different, short (usually <30 nucleotides) DNA fragments.
  • Olsen P Test
    An extractant used for soil testing of neutral and calcareous soils that estimates the capacity of a soil to supply available P.
  • Order
    A group of soils in the broadest category.  In the current system of soil classification in the U.S., there are 12 orders, differentiated by the presence or absence of diagnostic horizons: Alfisols, Andisols, Aridisols, Entisols, Gelisols, Histosols, Inceptisols, Mollisols, Oxisols, Spodosols, Ultisols, Vertisols. (adapted from SSSA)
  • Ordinary Superphosphate (0-20-0 + 12S)
    A material produced by reacting sulfuric acid with finely ground rock phosphate; about 85-90 percent water soluble.  An excellent source of phosphorus and sulfur.
  • Organelle
    An organ-like structure within a cell having a particular function.
  • Organic Chemical
    A chemical that is created naturally by using an organism(s) from the environment.
  • Organic Matter
    The total of the organic compounds in soil, exclusive of undecayed plant and animal tissues, their "partial decomposition" products, and the soil biomass. The term is often used synonymously with humus. (Glossary of Soil Science Terms. Soil Sci. Soc. Am. 1998)
  • Organic Matter, Soil
    Material that contains carbon and is found in the soil. Most soil organic matter comes from previously living organisms.  Temperature and moisture are the two main factors affecting its development.
  • Organic Molecule
    A molecule containing carbon atoms.
  • Osmoticum
    Particles that cause osmosis.
  • outcrop
    bedrock exposed at the surface of the earth

  • Ovary

    Lower part of the pistil that contain the ovules and ripens into a fruit.

  • oven-dry

    a soil sample that has been dried at a temperature of 105oC until the sample weight does not decrease (all moisture is removed).

  • Ovule

    Structure containing the embryo sac surrounded by the nucellus, found in seed plants. It turns into a seed after fertilization.

  • Oxidación
    La remoción de uno o mas electrones de una molécula. Para un metal como el fierro, la oxidación se muestra como un simple cambio de valencia (por ejemplo, Fe2+ es la forma reducida y Fe3+ es la forma oxidada). En cambio, en una molécula orgánica la remoción de electrones es usualmente acompañada por la remoción de protones (H+), y frecuentemente también por la adición de oxígeno o enlaces dobles.
  • Oxidation
    Removal or exchange of electrons usually by combining with oxygen.
  • Oxidation
    The removal of one or more electrons from a molecule. For a metal like iron, the oxidation appears as a simple change in valence (e.g. Fe2+ is reduced, Fe3+ is oxidized). For an organic molecule, the removal of electrons is usually accompanied by the removal of hydrogen atoms and often the addition of oxygen or double bonds.
  • p value

    In a chi-square analysis, the p-value is the probability of obtaining a chi-square as large or larger than that in the current experiment and yet the data will still support the hypothesis.  It is the probability of deviations from what was expected being due to mere chance.  In general a p value of 0.05 or greater is considered critical, anything less means the deviations are significant and the hypothesis being tested must be rejected.

  • P-680
    The reaction center of photosystem II which best absorbs light at a 680 nm wavelength. P-680 is a chlorophyll a molecule.
  • P-700
    The reaction center of photosystem I which best absorbs light at a 700 nm wavelength. P-700 is a chlorophyll a molecule.
  • Palatability
    Summation of plant characteristics that determine the relish with which a particular plant species or plant part is consumed by an animal.
  • Panicle

    An indeterminate inflorescence whose primary axis bears branches of pedicelled flowers.

    Armitage, A.;
    Herbaceous Perennial Plants


  • Paniculate

    An indeterminate inflorescence whose primary axis bears branches of pedicelled flowers.

    Armitage, A.;
    Herbaceous Perennial Plants


  • Pared Celular
    Una estructura delgada, mecánicamente fuerte que rodea a las células de las plantas. Consiste de una combinación de polisacáridos y otros polímeros que son secretados por la célula y que son ensamblados para formar una organizada red de compuestos ligados por enlaces covalentes y no covalentes. La pared celular regula el volumen celular y determina la forma de la célula.
  • parent material
    The unconsolidated, relatively unweathered minerals or organic matter from which soil develops.
  • Parent Material
    Rock or minerals which are weathered to form smaller particles of a soil. Parent material is one of the five factors contributing to formation of a specific soil. In the Great Plains, much parent material is associated with ancient seas or glacier deposits.
  • Particle Density
    The weight of an individual soil particle per unit volume. Particle density is usually expressed in units of grams per cubic centimeter (g/cm2). Bulk density considers both the solids and the pore space; whereas, particle density considers only the mineral solids.
  • PAT
    The enzyme that controls resistance of Liberty herbicide by detoxifying the herbicide molecule.
  • Patchy Distribution
    Close and often repeated grazing of small patches or even individual plants while adjacent similar patches or individual plants are lightly grazed or not grazed.
  • Pathogen
    A microorganism capable of causing disease.
  • Pathogens
    An agent that causes disease, especially a living microorganism such as a bacterium or fungus.
  • Pathway
    A sequence of interconnecting enzyme reactions.
  • PCR
    (polymerase chain reaction) A method for replicating a particular sequence of DNA in vitro. Used to generate greater amounts of DNA for analysis or to determine if a particular sequence exists.
  • Ped
    A unit of soil structure, formed together by joining fine sand, silt, or clay particles.
  • Pedicles
    Flower-bearing stems.
  • PEP carboxylase promoter
    Phosphenol pyruvate (PEP) carboxylase is an enzyme used in photosynthesis. The promoter of this gene induces protein production in actively photosynthesizing tissues of plants.
  • Percolation
    The downward movement of water through the soil, made possible by pore space in the soil.
  • Perennial

    A plant that lives three or more years.

  • Perfect
    A flower that has both functioning pistils and stamens.
  • Perfect Flower

    A perfect flower contains both male and female structures.

  • Permafrost
    Permanently frozen material underlying the solum.  (ii)  A perennially frozen soil horizon. 
  • Permanent Wilting Point
    The soil water content when a plant has extracted all the water it can. At this point, a plant will wilt and not recover.
  • Pesticide
    Any substance or mixture of substances used for controlling, preventing, destroying, repelling, or mitigating any pest. A pesticide also includes any substance or mixture of substances intended for use as a plant regulator, defoliant, or dessicant.
  • pH
    Negative log of the hydrogen ion concentration (pH = -log [H+]), the higher the pH of an environment the less H+ ion concentration, the more basic the environment becomes.
  • Phenotype
    The observable physical characteristics of an organism that are determined by a combination of the genetic composition (genotype) and the environment of the individual.
  • Phenotypic Trait
    An observable physical characteristic of an organism. See Phenotype.
  • Phenoxyacetic Acids
    A family of herbicides with similar chemical structure belonging to the growth regulating mode of action. An example would be 2,4-D.
  • Pheromone
    A chemical secreted by an insect or animal that influences the behavior of others within the same species; often functions as an attractant of the opposite sex.
  • Phloem
    Tissue used for the movement of sugars from source tissue to sink tissue; Composed of living cells called sieve elements that have no nuclei, vacuoles, or ribosomes. The ends of the sieve elements contain connective pores, which join them together to form tube-like structures.
  • pHopt
    The optimum pH for a reaction.
  • Phosphatase
    An enzyme produced by some algae species under conditions of low P availability.  Phosphatase converts organic P to inorganic P, which the algae can, in turn, use for growth.
  • Phosphate
    Used, instead of phosphorus, in fertilizer technology to refer to available phosphoric acid (P2O5).
  • Phosphatidylcholine
    A major lipid component of cell membranes containing equal amounts of saturated and monounsaturated fatty acids, phosphate, and choline; also called lecithin.
  • Phosphoinositide
    Phospholipids containing inositol involved in linking extracellular signals to intracellular responses, or signal transduction.
  • Phospholipid Molecules
    A lipid that is mostly nonpolar, but contains a charged phosphate group and possibly other polar functional groups at one end. This type of lipid is a primary component of biological membranes
  • Phosphorescence
    Light emitted by an excited triplet molecule as part of the de-excitation process. Because a significant amount of the energy in the original exciting photon is lost in the conversion from the excited singlet to the excited triplet state, the wavelength of phosphorescence is greater (i.e. less energy) than the wavelength of the exciting photon and greater than the wavelength of any fluorescence from the excited singlet state in that molecule.
  • Phosphoric Acid (0-54-0)
    Material produced by treating finely ground rock phosphate with sulfuric acid or by smelting (burning) rock phosphate with coke and silica in an electric furnace and reacting with water. Agricultural grade phosphoric acid is seldom used for direct application because of its corrosive properties; it is usually used to make other forms of phosphoric fertilizers.
  • Phosphorus
    A key element in the complex nucleic acid structure of plants which regulates protein synthesis; important in cell division and development of new tissues.  Next to nitrogen, the most limiting nutrient in Nebraska crop production; naturally found in sufficient amounts in many Nebraska soils.
  • Phosphorus, Bio-available
    This water P fraction, also refer to algal-available P, is a combination of dissolved P plus the estimated portion of P to be released from sediment P within a short time, e.g. 45 hours, after the particles enter surface water.
  • Phosphorus, Dissolved
    This water P fraction, a near equivalent with dissolved reactive P, is readily available to aquatic plants and animals.
  • Phosphorus, Labile
    This soil P fraction is typically accounts for less than 1% to less than 5% of the P in soils, and is less tightly bond than stable P. Some labile P, as well as solution P, is measured with agronomic soil tests.
  • Phosphorus, Sediment
    This water P fraction, also referred to as particulate P, often is the greatest fraction in water bodies. It consists of organic and inorganic sediments. Its not available to most aquatic plants and animals, but phosphatase producing algae can cause organic sediment P to become available.
  • Phosphorus, Solution
    This soil P fraction is typically accounts for less than 1% of the P in soils and is readily available to plants.
  • Phosphorus, Stable
    This soil P fraction is also called non-labile P. It accounts for most of the P in soils, typically more than 95% of the total, and includes tightly bond P in secondary and primary minerals and in organic forms.
  • Phosphorylation
    the attaching of a phosphate group to a substrate
  • Phosphotidylinositol
    A a membrane lipid called a phosphoinositide. Phosphoinositides are phospholipids containing inositol involved in linking extracellular signals to intracellular responses, or signal transduction.
  • Photomorphogenesis
    The development of a plant cell or organ that is triggered by exposure to light. For example, if a corn plant is germinated in the dark, it will produce an etiolated shoot, lacking chlorophyll or the ability to carry out photosynthesis. Exposing an etiolated shoot to light will initiate development of pigment biosynthesis and the production of cellular components necessary for photosynthesis.
  • Photon

    The basic unit of light. Although light has some properties consistent with a wave, light from the sun is in individual packages. Each photon is a particle of electromagnetic radiation traveling with the speed of light (3 X 108 m sec-1). The energy in each photon is dependent on the frequency with which the electromagnetic field vibrates.

  • Photophosphorylation

    The coupling of photosystems I and II with an electron transfer chain that moves electrons from water (which is oxidized to form O2) to NADP+ (which is reduced to form NADPH). The transfer of electrons between photosystem II and photosystem I releases energy, which is conserved in the form of a trans-membrane proton gradient and used to synthesize ATP.

  • Photosensitizers

    Molecules which have efficient conversions to the triplet state after absorption of a photon. These triplet state molecules either reduce other molecules to generate free radicals, or they excite O2, normally a triplet, to the excited singlet state; singlet oxygen is very reactive and can cause significant cellular damage.

  • Photosynthesis
    The process in which plants use light energy to make sugars and other organic food molecules from carbon dioxide and water.
  • Photosynthetic Inhibitors
    The mode of action of a group of herbicides that directly influence the light reaction of photosynthesis.
  • Photosystem
    An array of pigment-protein complexes and electron transfer components that function together to harvest light energy, transfer the energy to photochemical reaction centers, and move the excited electrons in a controlled fashion to produce usable biochemical energy. Each photosystem contains hundreds of chlorophyll and carotenoid molecules functioning as antennae, while only a few chlorophyll molecules are employed in the reaction centers.
  • Physical Structure
    The combination or arrangement of soil particles into secondary units or peds. (Glossary of Soil Science Terms. Soil Sci. Soc. Am. 1998)
  • Physicochemical
    The set of physical and chemical properties characteristic of a given molecule.
  • Phytohormones
    Compounds produced by the plant to regulate growth and development of the plant.
  • Phytotoxic
    A substance which is toxic to plants.
  • Pigment Synthesis Inhibitors
    The mode of action of a group of herbicides that stops pigment synthesis (not chlorophyll)i these pigments are present to protect chlorophyll from breakdown by sunlight. Without the pigments present, chlorophyll is easily degraded showing bleaching symptoms on plant tissue.
  • Pipette
    A tool used to accurately dispense specific amounts of a liquid.
  • Pistil
    The female reproductive structure in plants; the stigma, style and ovary collectively.
  • Pistil

    Organ of a flower that contains ovules, including the style, ovary and stigma.

  • pKa
    the specific equilibrium (or ionization) constant (K) defines the concentration of an acid and its conjugate base in solution at a specified temperature. pKa is -log of Ka. Ka is the acid dissociation constant described by Ka = [H+][A-]/[HA] where HA is an acid, and the quantities in brackets are molar concentrations. K is any equilibrium constant. Ka is the equilibrium constant that describes a particular type of chemical reaction, in this case an acid dissociation.
  • pKa
    The dissociation constant of an acid; the pH at which 50% of the molecules are associated (have the H+ ion) 50% are dissociated (lost the H' ion).
  • Plan
    Shape of the slope viewed from the top (map view, bird's-eye view).
  • Plant Available Water
    That portion of soil water that can be absorbed by a plant. Generally, plant available water is considered to be 50 percent of the water holding capacity.
  • Plasma Membrane
    The semi-permeable membrane that surrounds the protoplasm of a cell.
  • Plasmid
    A small circular piece of DNA from bacteria that often contains antibiotic resistance genes. Some types have the capability to be replicated in the bacteria and integrate itself into the genome of a plant.
  • Plasmodesmata
    Narrow extensions of cell sap through cell walls.
  • Plasmodesmos
    Estructuras entre las células, que forman canales o extensiones angostas de savia celular a través de las paredes celulares.
  • Plastids
    Pigmented cytoplasmic organelles found in plant cells and other organisms; includes chloroplasts and mitochondria.

  • Pleiotropy
    The control of more than one trait by a single gene.
  • Ploidy
    The number of sets in a cell of basic chromosomes; often affects plant vigor, flower size and number, and ability to hybridize; an important fact in daylilies and orchid species.
  • Plow
    Operation that completely turns the soil over to a depth of about 8 inches; uses a moldboard plow.
  • Polar
    More hydrophilic or water loving.
  • Polar Axis of Plant
    The longitudinal directions a plant grows.
  • Polar Functional Groups
    Functional groups with atoms such as O, N, S or P which do not equally share the electrons in the bonds, resulting in dipole moments
  • Polar Molecules
    Molecules with functional groups containing dipole moments (e.g., alcohols, carbonyls, amides, amines).
  • Polar Solvent
    A solvent with molecules containing functional groups with dipole moments.
  • Polarity
    Property of a covalent bond or an entire molecule that results in a negative pole and a positive pole; A bond becomes polar if the electrons involved in the bond are not shared equally. Polarity results when the center of the negative charge does not coincide with the center of the positive charge.
  • Pollen
    Dust-like material produced by the anther (male reproductive structure) that is composed of pollen grains (microgametophytes) which carry the male gametes of seed plants; important in fertilization.
  • Pollination

    To transfer pollen from an anther to the stigma of a flower.

  • Polymerase Chain Reaction (PCR)
    The lab procedure which makes copies of DNA much like cells replicate DNA during cell division.
  • Polymorphic
    Existing in multiple forms. When a marker locus is polymorphic, there are detectable differences in DNA sequence at that locus.
  • Polypliody

    An organism with more than two sets of chromosomes.

  • Polyploid
    An organism or cell having more than two complete sets of chromosomes.
  • Polyploidy
    Having more than 2n (diploid) number of basic chromosomes such as triploid (3n) or tetraploid (4n); very common in angiosperms.
  • Pore Space
    Spaces in soil, between the mineral and organic matter, that are filled with water or air.
  • Porosity
    The volume of soil voids that can be filled by water and/or air; inversely related to bulk density.  Porosity is also known as "pore space."
  • Postemergence
    Application of a herbicide after the plant has emerged.
  • Postzygotic Mechanisms
    Barriers to gene flow between to two populations after fertilization, causing reproductive isolation that leads to two different species (genotype) of an organism; but they may not be distinguishable by appearance (phenotype).  Barriers include death of zygote, hybrid inviability, hybrid sterility, and hybrid breakdown (reduced viability and fertility of second generation).
  • Potassium
    An essential plant nutrient needed in large amounts.  Postassium is vital to plant nutrient absorption, respiration, transpiration and enzyme activity. The major portion of potassium is contained in minerals such as feldspar and mica, and clays such as montmorillonite, vermiculite and illite.
  • Potassium Chloride (0-0-60)
    The most commonly used and most economical potassium fertilizer.  It is mined as sylvinite from underground mines or by solution mining in New Mexico, Utah, California and Michigan.
  • Potassium Sulfate (0-0-50 + 18S)
    Material used as a potassium fertilizer for crops where the chloride content of potassium chloride is undesirable.
  • Potassium-Magnesium Sulfate (Sul Po Mag)(0-0-22 + 22S)
    A double salt of potassium and magnesium sulfate; commonly used as a dry granular source of potassium, magnesium and sulfur.
  • Potencial Osmótico
    El efecto de los solutos disueltos sobre el potencial hídrico.
  • PPO
    Protoporphyrinogen oxidase (protox); enzyme utilized in photosynthesis and is the target site of many herbicides in the cell membrane disrupter mode of action.
  • Preference
    Selection of certain plants, or plant parts, over others by grazing animals.
  • Presión de Turgencia
    La presión positiva que se crea cuando el agua es comprimida.
  • Prezygotic Mechanisms
    Barriers to gene flow between two populations berfore fertilization, causing reproductive isolation leading to two different species (genotype) of an organism; but they may not be distinguishable by appearance (phenotype).  Barriers include geographical isolation, egolocial isolation, seasonal isolation, behavioural isolation, mechanical isolation, and gametic incompatibility
  • Primer
    Small section of DNA nucleotides which bind to the single-stranded DNA template during PCR. These can be sequences specific for a gene or totally random, depending upon the experiment’s objective.
  • Primer Annealing Step
    The second step of PCR. In this step the primers will bind to their complementary DNA sequences on the single-stranded DNA template.
  • Primer-Dimers
    Primer-dimers occur when single-stranded primer oligonucleotides bind to each other rather than the DNA template.
  • Principal Component Analysis/Cluster Mapping
    A statistical method of reducing a dataset of two or more correlated variables, usually resulting in a regression relationship, in order to detect inherent structure.
  • Pro-Herbicide
    A molecule that doesn't become herbicidally active until a reaction within a plant makes it a herbicide.
  • Probe
    A macromolecule such as DNA or RNA that has been labeled with either radioactivity or antibodies and can be detected by an assay. Probes are used to identify target molecules, genes, or gene products.
  • Procambium
    The tissue in the central portion of an embryo.
  • Proembryonal Complex
    A mass of embryogenic cells.
  • Profile
    The shape of a slope profile. Profile is the slope viewed in a vertical cross-section.
  • Progenitor Cell
    A cell that is able to produce embryogenic cells by cell division.
  • Progeny
    The offspring of an organism.
  • Progeny Testing
    A test of the value of a genotype based on the performance of its offspring produced in some definite system of mating.
  • Promoter
    A specific DNA sequence to which RNA polymerase binds and initiates transcription. This region contains information which regulates when and how often the gene is transcribed and ultimately the amount of protein it produces.
  • Promotor
    Una secuencia específica de ADN a la cual se enlaza la ARN-polimerasa (RNA-polymerase) para iniciar la transcripción. Esta región contiene la información que regula cuando y con que frecuencia un gen es transcrito y la cantidad de proteína que éste produce.
  • Propagate

    using plant tissue to generate new plants.

  • Propanoic Herbicides
    A family of herbicides that have similar chemical structure and belong to the lipid synthesis inhibiting mode of action (fops).
  • Protein
    A large molecule composed of one or more chains of amino acids in a specific order. Proteins are necessary for the structure, function, and regulation of an organism's cells, tissues, and organs. Each protein has a unique function determined by its shape.
  • Protein Kinases
    Enzymes that phosphorylate proteins using ATP.
  • Protein Synthesis
    The production of proteins in a cell. Proteins are chains of amino acids linked in the order determined by the genetic code.
  • Proteins
    Large molecules composed of one or more chains of amino acids in a specific order. Proteins are necessary for the structure, function, and regulation of the organism's cells, tissues, and organs. Each protein has a unique function determined by its shape.
  • Proteomics
    A system for identifying proteins within a cell or tissue sample.
  • Proteína
    Una macromolécula formada por una o mas cadenas de aminoácidos, en un orden preestablecido. Las proteínas son necesarias para la estructura, regulación y funcionamiento de las células, tejidos y órganos de los organismos. Cada proteína tiene una función única que está determinada por su forma.
  • Proteínas
    Macromoléculas formadas por una o mas cadenas de aminoácidos unidos en un orden específico. Las proteínas son necesarias para la estructura, regulación y funcionamiento de las células, tejidos y órganos de los organismos. Cada proteína tiene una función única que está determinada por su forma.
  • Proteínas Kinasas
    Enzimas que fosforilan proteínas usandoATP.
  • Protoderm
    A primary embryonic tissue that is located on the surface of young embryos.
  • Proton
    A positively-charged atomic particle; a hydrogen ion H+.
  • Proton Motive Force (PMF)
    Created when protons are extruded from the cytosol by electrogenic H+-ATPases, both at the plasma membrane and the tonoplast, a membrane potential and a pH gradient are created at the expense of ATP hydrolysis. This gradient of electrochemical potential for H+ represents stored free energy in the form of the H+ gradient.
  • Proton-ATPase

    A membrane protein located in the plasma membrane and tonoplast, used to carry out primary active transport of H+ out of the cytoplasm by coupling directly to the energy released during ATP hydrolysis.

  • Protonated
    Having a proton attached, usually it is a H+ when considering herbicides.
  • Protoplasm
    All the substance of a cell, usually considered not to include the cell wall. The protoplasm of a single cell is a protoplast.
  • Protoplast
    A plant cell that has had the cell wall removed.
  • Protoporfirina
    Un producto intermedio en las rutas biosintéticas de las clorofilas y los grupos hemo. Esta molécula es un fuerte fotosensibilizador y causa mucho daño celular si se acumula en tejidos expuestos a la luz.
  • Protoporphyrin
    An intermediate in the biosynthetic pathways for chlorophyll and heme. This molecule is a strong photosensitizer and causes much cellular damage if it accumulates in tissues exposed to light.
  • Pubescent
    Covered with hairs; ex. Stachys, Pulsatilla.
  • Pupa
    The nonfeeding stage between the larva and adult.  The organism undergoes a complete transformation within a protective cocoon or hardened case.
  • Pyramid

    as it relates to GMOs, refers to the use of multiple events that target the same pest or pest complex.

  • Péptido de Transporte
    Secuencia especial de aminoácidos que se encuentra al final de una proteína para guiarla al sitio donde es requerida dentro de la célula.
  • QTL
    Quantitative trait locus. (1) a locus that influences the expression of a quantitative trait. (2) a chromosome region detected by statistical analysis that is significantly associated with variation for a quantitative trait.
  • Qualitative Characters
    A character in which variation is discontinuous.
  • Quantitative Characters
    A character in which variation is continuous so that classification into discrete categories is not possible.
  • quantitative trait

    A trait whose inheritance is due to one or a few genes working together.  Phenotypic classes are not continuous so classification into discrete categories is possible.  An example of this would be herbicide resistance in crop species.

  • Quantitative Trait Locus
    Quantitative trait locus. (1) a locus that influences the expression of a quantitative trait. (2) a chromosome region detected by statistical analysis that is significantly associated with variation for a quantitative trait.
  • Quenching
    The process of causing the de-excitation of a molecule from an excited singlet or triplet state back down to the ground state. Quenching of chlorophyll is an important protective role of carotenoids. If a triplet molecule is not rapidly quenched, it can react with oxygen to generate singlet oxygen. Singlet oxygen can cause much cellular damage.
  • Raceme

    A simple, indeterminate inflorescence with pedicelled flowers.

    Armitage, A.;
    Herbaceous Perennial Plants

  • Radical Libre
    Una molécula con un electrón no apareado en uno de sus orbitales. Los radicales libres son extremadamente reactivos, pudiendo dañar a una gran variedad de moléculas celulares.
  • Radicales Libres
    Moléculas con un electrón no apareado en uno de sus orbitales. Los radicales libres son extremadamente reactivos, pudiendo dañar a una gran variedad de moléculas celulares.
  • Range Condition
    The present state of vegetation of a range site in relation to the natural potential plant community for that site.
  • Rangeland
    Land on which the native vegetation is predominantly grasses, grass-like plants, forbs, or shrubs.
  • RAPD
    Random Amplified Polymorphic DNA. These markers involve PCR amplification of DNA fragments using primers that are random 10-base oligonucleotides. A single RAPD reaction may amplify several to many DNA fragments. RAPDs are dominant markers and, therefore, less informative than codominant markers because heterozygous individuals cannot be identified. A major advantage is that no prior knowledge of an organism's genome is necessary for their use. A common problem with RAPDs has been lack of reproducibility among labs. The technique is described in more detail in S. Grandillo and T.M. Fulton (2002), Approaches to gene mapping. pp. 101-136. In P.M. Gilmartin and C. Bowler (ed.) Molecular Plant Biology Vol. 1. Oxford Univ. Press, Oxford and New York.
  • Ray Floret

    A radiating part of the flower or plant; The marginal florets of a compound flower, as an aster or a sunflower.

  • Reaction Center
    A specialized component of the photosystem that actually carries out the photochemistry with the excitation energy harvested by antenna pigments.
  • Receptacle
    The expanded end of a pedicel (stalk) that holds the flowers or floral organs.
  • Receptor
    Proteínas especiales en la membrana celular que captan una señal o mensaje químico del ambiente y lo transmite a la célula para iniciar una respuesta.
  • Receptor
    Special proteins in the cell membrane that bind to a signal or chemical messenger from the environment and transmit signals to the cell to initiate a response.
  • Recessive
    A trait that will not be expressed unless there are two copies of the gene allele present in an organism.
  • Recessive Allele
    An allele whose phenotype is not expressed in a heterozygote.
  • Reciprocal Cross

    Hybridization involving a pair of crosses that reverse the sexes associated with each genotype.

  • Recombinant DNA
    DNA that has been altered and is different from the original sequence.
  • Recombinant Plasmid
    A plasmid that has been cut with special enzymes and "recombined" in a new order or with DNA from another source.
  • Recombination Frequencies/Map Distance
    Recombination frequency is the frequency of crossovers between two genes. The map distance (in this case a genetic or recombinational map) is the recombination frequency between two genes times 100. For example, if the frequency of recombination is 0.10, the map distance is 10 map units.
  • Recurrent Parent
    The parent to which successive backcrosses are made in backcross breeding.
  • Reducción
    El proceso inverso a la oxidación. Una molécula se reduce cuando gana uno o mas electrones.
  • Reduction
    The opposite of oxidation. When a molecule acquires one or two electrons it becomes more reduced.
  • Refuge

    a stipulation of Environmental Protection Agency (EPA) registration of GM crops containing Bt traits be planted along with a specified acreage (expressed as a percentage) of a non-traited crop of the same species and managed similarly.  This area serves to rear insects that are not subject to the Bt toxin and the related selection pressure for resistance management.

  • Refuge

    A specific area of non-Bt corn planted into a Bt corn field to allow for survival of susceptible insects which can breed with resistance individuals to manage Bt resistance and keep genetic resistance manageable.    

  • Regiospecificity
    The ability of an enzyme to target a particular bond with in a molecule.
  • Regulatory Protein
    A protein that binds to the promoter of a gene to regulate transcription.
  • Relative Fitness
    The fitness of one genotype when compared with another.
  • Relative Humidity
    The ratio of the amount of water vapor actually present in the air to the greatest amount possible at the same temperature.
  • Rendimiento Potencial
    El máximo rendimiento que una planta (híbrido, variedad, etc.) es capaz de producir cuando crece bajo condiciones ambientales ideales.
  • Replicate
    The copying of a DNA molecule in a cell.
  • Replicated
    Copied DNA. To make copies of DNA.
  • Replication
    The copying of a DNA molecule.
  • Resistance
    The inherited ability of a population to survive and reproduce following repeated exposure to a dose of herbicide normally lethal to the wild type. Resistance may also be induced by such techniques as genetic engineering or selection of variants produced by tissue culture or mutagenesis.
  • Resistance
    The ability of an organism to survive and thrive in the presence of something that would normally cause damage or death, i.e., herbicide-resistant corn, Roundup-ready corn.
  • Resistant
    The inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type. In a plant, resistance may be naturally occurring or induced by such techniques as genetic engineering or selection of variants produced by tissue culture or mutagenesis.
  • Resistencia
    La oposición ofrecida al paso del agua a través de un sistema de interés.
  • Resistente
    La habilidad heredada que posee una planta para sobrevivir y reproducirse después de ser expuesta a una dosis de herbicida que normalmente es letal para una planta del genotipo original. La resistencia de una planta a un herbicida puede ocurrir de manera natural o como resultado del empleo de técnicas de ingeniería genética o selección de variantes producidas mediante cultivo de tejidos o mutagénesis.
  • Respiración
    El proceso químico por el cual azucares simples como la glucosa son oxidados a bióxido de carbono y agua con la liberación de energía en forma de ATP.
  • Respiration
    The chemical process by which simple sugars such as glucose are oxidized to carbon dioxide and water with the liberation of energy in the form of ATP.
  • Restriction Enzymes
    Enzymes that are able to detect a particular nucleotide sequence and cut the DNA, RNA, or protein at that location.
  • Retrocruzamiento
    Método de fitomejoramiento empleado para mover uno o solo unos pocos genes deseables de una línea agronómicamente pobre a una línea élite. Esto se hace mediante el cruzamiento de una línea donante con una línea élite y cruzando la progenie conteniendo los genes deseados nuevamente con el progenitor élite.
  • RFLP
    Restriction Fragment Length Polymorphism. DNA is digested with a restriction enzyme and the fragments are separated by electrophoresis. The DNA fragments are then transferred to a membrane and hybridized with a labeled DNA probe. Polymorphisms are detected as labeled DNA fragments of different sizes. RFLPs are very informative due to their codominant nature (they distinguish between homozygotes and heterozygotes). Large numbers of RFLP markers are available for many species. Disadvantages are that they are relatively expensive and time consuming, and they require a large quantity of DNA. Most commonly, radioactive labeled probes are used, but non-radioactive methods are also available. The technique is described in detail in S. Grandillo and T.M. Fulton (2002), Approaches to gene mapping. pp. 101-136. In P.M. Gilmartin and C. Bowler (ed.) Molecular Plant Biology Vol. 1. Oxford Univ. Press, Oxford and New York.
  • RFLP Mapping
    (Restriction Fragment Length Polymorphism)  A technique which uses restriction enzymes to cut DNA and then compare the different sizes of specific fragments created with those from another individual to determine genetic difference.
  • RH
    Relative humidity.
  • Rhizomatous
    Having or looking like a rhizome.
  • Rhizome

    A horizontal, usually underground stem that often sends out roots and shoots from its nodes.

  • Rhizomes
    A specialized horizontal stem that gives rise to shoots and roots at its nodes; usually found underground, i.e., iris, rhubarb.
  • Ribosome
    A large molecule that catalyzes the translation of mRNA codons into an amino acid sequence.
  • Rill
    A small, intermittent water course with steep sides, usually only several centimeters deep.
  • Rill Erosion
    The erosion process which causes the formation of numerous small channels of less than to two to three inches deep.
  • RNA
    Ribonucleic Acid.  A single-stranded nucleic acid similar to DNA but having a uracil rather than thymine as one of the nucleotides. The RNA strand carries the coded information from the nucleus to the cytoplasm where protein production occurs.
  • RNA Polymerase
    An enzyme that catalyzes the synthesis of RNA by copying the nucleotide sequence of the DNA.
  • Rootstock

    A root or part of a root used as a stock for plant propagation.

  • Roundup
    A herbicide that provides non-selective control of several annual and perennial weeds. Roundup will also damage crops, such as corn and soybeans that are not Roundup-resistant.
  • Roundup
    A herbicide that provides non-selective control of several annual and perennial weeds. Roundup will also damage crops, such as corn and soybeans, that are not Roundup-resistant.
  • Roundup-Ready
    A trade name given to certain varieties of corn or soybean which are resistant to the herbicide, Roundup, whose active ingredient is glyphosate.
  • Roundup-Resistant
    A plant that is not harmed by the application of Roundup herbicide, i.e., Roundup Ready Corn, Roundup Ready Soybeans.
  • RT-PCR
    Real-time PCR.  This is a term used to describe PCR methods which detect DNA amplification in "real time" as the experiment is taking place, rather than at the end of the experiment.
  • Runoff
    The portion of precipitation or irrigation on an area that does not infiltrate but, instead, is discharged from the area. That which is lost without entering the soil is called "surface runoff."
  • Ruta Apoplástica
    El agua se mueve por las paredes celulares o la región no viva entre las células, sin cruzar membranas.
  • Ruta Celular
    El agua se mueve de célula a célula a través de las membranas, ya sea cruzándolas o usando los plasmodesmos.
  • Ruta de Traducción de Señales
    Proceso por medio del cual un receptor inicia una o más secuencias de reacciones bioquímicas que conectan un estímulo con una respuesta celular.
  • Ruta Metabólica
    Una secuencia de reacciones interconectadas, catalizadas por enzimas.
  • Ruta Metabólica del Shikimato
    Es la ruta metabólica de las plantas responsable de la producción de los aminoácidos aromáticos y otros productos.
  • Ruta Simplástica
    El movimiento del agua de una célula a otra por medio de los plasmodesmos.
  • Ruta Transmembranal
    La ruta seguida por el agua que secuencialmente entra por un lado de la célula, sale por el lado opuesto, entra a la siguiente célula y así sucesivamente. En esta ruta, el agua cruza al menos dos membranas de cada célula involucrada.
  • Safener
    A chemical agent that reduces toxicity of herbicides to crop plants by a physiological or molecular mechanism.  Safeners are also known as antidotes, antagonists or crop protectants.
  • Safener
    A compound used in conjunction with a herbicide to provide extra protection to the crop without reducing weed control.  A safener usually acts by increasing GSH and GST levels and activity.
  • Salinity
    The amount of soluble salts in a soil. The conventional measure of soil salinity is the electrical conductivity of a saturation extract, usually in units of deciSiemens per meter (dS m-1). (SSSA and Dennis McCallister)
  • Saltation
    The detachment of soil particles from aggregates due to the impact of windblown soil particles.
  • sand

    A soil inorganic particle in the range of 50 to 2000 μm (.05 to 2.0 mm) diameter in the USDA classification system. Sand is also a textural class name for a soil having at least 85% sand-sized particles.

  • Sand
    Individual rock or mineral fragments in a soil that range from 0.05 to 2.0 millimeters in diameter. Most sand grains consist of quartz, but they can be of any mineral composition.  Sand is also the textural class name of any soil that contains 85 percent or more sand and no more than 10 percent clay.
  • Saturation
    Soil conditions where all the pores are completely filled with water. The soil tension exhibited on water under this condition is zero, and gravitational is the dominant force moving water downward.
  • SCAR
    Sequence characterized amplified region. To improve their specificity and repeatability, a RAPD or AFLP marker can be converted into a SCAR marker. SCARs are developed by obtaining the DNA sequence of a RAPD or AFLP band and designing 18-25 base PCR primers to amplify the same DNA segment. SCARs are easier to employ in marker-assisted selection than RAPDs or AFLPs.
  • Secondary Embryogenesis
    The development of embryos from young embryos.
  • Secondary Messengers
    Transient secondary signals inside the cell that greatly amplify the original signal.
  • Sediment
    Eroded particles that are no longer part of the soil. These sediments, sand silt, or clay size, are carried by wind or water and deposited to a different area, like surface water bodies. Sedimentation occurs when eroded soil is deposited and/or settles in water. Erosion, itself, is the process of detaching and transporting soil particles.
  • Sedimentation
    Occurs when eroded soil deposits and/or settles out in water.
  • Seedling Growth Inhibitors
    Mode of action of a group of herbicides that generally disrupt early growth of plants.
  • Segregating Population
    A collection of lines from a cross or population that is undergoing Mendelian or Hardy-Weinberg gene segregation.
  • Segregation Distortion
    Deviation of the expected segregation ratio from that expected by Mendelian inheritance. Distorted segregation means that either the maternal or paternal allele was transmitted to the progeny at a higher frequency than expected.
  • Selectable Marker Gene
    A gene encoding an easily detectable trait transferred into a cell with another gene encoding a less detectable trait. The selectable marker gene allows genetic engineers to select transgenic cells and plants from those that are non-transgenic.
  • Selection Media
    Agarose media containing the substance for which the selectable marker gene encodes resistance. When tissue culture cells are place on this media, cells that have not been transformed and do not contain the gene conferring resistance to the substance will die leaving only those cells that are transgenic.
  • Selection Pressure
    The process that changes the relative frequency of one or more genes within a population.
  • Selective
    Herbicides which cause one species of plants to die, but another species will survive the same treatment. Selectivity allows for acceptable weed control without injury to crop plants.
  • Selective Grazing
    Taking certain plant species, individual plants, or plant parts to the exclusion of others.
  • Selectividad
    Implica que diferentes especies vegetales no responden de la misma manera a un herbicida particular. Los herbicidas que causan la muerte de una especie de plantas pero no la muerte de otra especie son herbicidas selectivos. La selectividad permite un control aceptable de malezas sin dañar a los cultivos.
  • Selectivity
    Differential effect of a herbicide when applied to a mixed population of plants; sensitive plants die, tolerant plants are unharmed. Implies that different plant species do not respond in the same way to a particular herbicide. Herbicides which cause one species of plants to die, but not another, are selective. Selectivity allows for acceptable weed control without injury to crop plants.
  • Selectivo
    Un herbicida que causa la muerte de una especie de plantas, mientras que otra especie sobrevivirá al mismo tratamiento. La selectividad permite el control aceptable de malezas sin afectar a las plantas cultivadas.
  • Senesces
    The end of a plant's life cycle when it reaches maturity and leaves dry up.
  • Sepals
    A modified leaf which is usually green and part of the caylx; can protect the flower when in bud.
  • Sequencing
    Determination of the order of nucleotides in a DNA or RNA molecule or the order of amino acids in a protein.
  • Sessile
    Without a petiole (leaf) or pedicel (stalk of a flower).
  • Shattercane
    Sorghum bicolor.  A summer annual that resembles grain sorghum and corn. It is derived from wild and/or cultivated sorghum varieties. Shattercane is a major weed problem in corn, sorghum, and soybean fields in the Central United States. (California, 2001)
  • Shear Strength
    The ability of a soil or rock to resist shearing (tangential) forces and/or stresses.
  • Sheet Erosion
    The removal of a relatively uniform thin layer of soil for the land surface by unchanneled runoff, or sheet flow.
  • Shikimate Pathway
    Important chemical pathway in plants. It is responsible for producing amino acids and other aromatic products.
  • Shoot
    Portion of the developing seedling above the root system.
  • Shrink-Swell Potential
    The susceptibility of a soil to a change in volume due to a loss or gain in moisture, especially those soils with a relatively high clay content.
  • Signal Transduction Pathway
    The process whereby a receptor initiates one or more sequences of biochemical reactions that connect the stimulus to a cellular response.
  • Silt
    A soil inorganic separate in the range of 2 to 50 micrometers (or 0.002 to 0.05 mm.). Silt is smaller than sand but larger than clay.
  • Single-Seed Descent
    Breeding procedure in which progenies of a segregating population are self-pollinated and advanced to the next generation by a single seed in each progeny line.
  • Singlet States
    An orbital to which an electron may move after being excited by a photon. Singlet state orbitals require that the excited electron have a spin opposite to that of the spin on the electron remaining in the ground state.
  • Site of Absorption
    Site of Absorption is the location where the herbicide is taken up by the plant. This should not be confused with Site of Action which is the biochemical pathway within the plant where the herbicide acts.
  • Site of action
    In a biochemical pathway, the point at which a herbicide functions.
  • Site of Action
    The Site of Action is the biochemical pathway a particular herbicide acts upon in a plant. Currently there are over 20 sites of action
  • Site of Uptake
    Site of Uptake is the location where the herbicide is taken up by the plant. This should not be confused with Site of Action which is the biochemical pathway within the plant where the herbicide acts.
  • SNP
    Single Nucleotide Polymorphism. A single position in a given DNA sequence that contains allelic variations within a population at relatively high frequencies. For example, replacement of a guanine (G) with a thymine (T) nucleotide is an example of a SNP. SNPs occur often in many genomes, thus facilitating the development of high-density marker maps. For further discussion of SNP applications in plants see J.A. Rafalski, 2002, Plant Science 162:329-333.
  • Soil
    The top layer of the Earth’s surface, consisting of four major components: air, water, organic matter and mineral matter. There are three categories of soil particles--sand, silt and clay--which are called "soil separates."
  • Soil Age
    Determined by the amount of weathering that has occurred; to what extent the parent material has been converted to distinct horizons or soil layers.  Usually described as young, mature or old.
  • Soil Aggregation/Aggregates
    The process of soil particles binding together. The mineral components of soil are clay, silt and sand. Clay particles are too small to be seen with a light microscope, and sand particles can be seen with the naked eye. Silt particles are of intermediate size. Without soil aggregation, soils would not have pores large enough for movement of air and water, and roots would not be able to penetrate the soil.
  • Soil Air
    The soil atmosphere; the gaseous phase of the soil, being that volume not occupied by solid or liquid. (1997. Soil Science Society of America. p. 94)
  • Soil Classification
    A specific soil is classified according to the number of horizons in its soil profile and the soil properties of each horizon. Well developed soils are old and contain all three master horizons (A, B, and C), as well as several subdivisions of the master horizons.
  • Soil Development
    Five factors influence the development of a specific soil:  parent material, climate, living organisms, topography and time.
  • Soil Forming Factors
    The variables, usually interrelated natural agencies, that are active in and responsible for the formation of soil. The factors are usually grouped into five major categories as follows: parent material, climate, organisms, topography, and time. (SSSA)
  • Soil Horizons
    A layer of soil or soil material approximately parallel to the land surface and differing from adjacent genetically related layers in physical, chemical, and biological properties or characteristics such as color, structure, texture, consistency, kinds and number of organisms present, degree of acidity or alkalinity, etc. (SSSA)
  • Soil Organic Matter
    The organic fraction of the soil, exclusive of undecayed plant and animal residues. See also "humus."
  • Soil Sample
    A collection of individual cores from a known area.
  • Soil Series
    A unit of soil classification determined by studying horizon characteristics, such as: number of horizons, color, thickness, texture, erosion phase, slope, organic content and depth to hardpan. All soils given the same soil series name possess the same characteristics across the landscape.
  • Soil Series
    The lowest category of U.S. system of soil taxonomy. (SSSA)

  • Soil Structure
    The arrangement of soil separates into units called soil aggregates.
  • soil taxonomy

    The classification and naming of soils. See Table 1.1 for a list of taxonomic levels and the number of classes for each level. Table 1.2 provides the taxonomy of the Nebraska state soil, the Holdrege silt loam.

    Table 1.1. Classification scheme for soils (Soil Survey Staff, 1999)

     Taxonomic Level

     Number of Classes

     Examples (Abbreviations)



    Alfisol (alf) — deciduous forest
    Andisol (and)— volcanic
    Aridisol (id) — dry/arid, desert
    Entisol (ent) — beginning: no horizon
    Gelison (el) — permafrost
    Histosol (ist) — organic; boggy
    Inceptisol (ept) — young; few horizons
    Mollisol (oll) — soft; grasslands
    Oxisol (ox) — oxide; tropical
    Spodosol (od) — mineral; coniferous
    Ultisol (ult) — last; hot, humid
    Vertisol (vert) — invert; swelling



    Saprist — sphagnum
    Humod — organic
    Andept — volcanic

     Great Group


    Borosaprist — frigid
    Cryohumod — colder than frigid
    Dystradept — low base saturation



    Fluvaquentic — flood plain
    Borosaprist — wetness
    Lithic — weathered Rock
    Aquic — wetness



    Coarse-silty — texture, mineralogy
    Mixed, mesic — temperature regime

     Series Texture


    McCook loam — surface Soil

    Table 1.2. Taxonomy of Holdrege silt loam soil

     Holdrege silt loam, fine-silty, mixed, mesic, Typic Argiustoll

    Formative Element

    Major Features


    Mollisol: grasslands soil; thick dark-colored surface horizon (mollic epepedon) with high base saturation and strong structure.


    Ustic soil moisture regime; intermediate between aridic and udic soil moisture regimes; limited moisture, but moisture is present at a time when conditions are suitable for plant growth.


    Argillic horizon; substantial amounts of clay have moved out of the surface soil and accumulated in this subsoil horizon; it may be below or within the mollic epipedon.


    Typical: the soil profile represents the central concept for the great group.


    Mesic soil temperature regime; mean annual soil temperature is 8oC or higher but lower than 15oC, and the difference between mean summer and mean winter soil temperature is more than 5oC at a depth of 50 cm.


    Mixed clay mineralogy; has less than 50 percent of any one mineral such as halloysite, kaolinite, monmorillonite, illite, vermiculite and chlorite.


    Particle size class; by weight, <15 percent of the particles are fine sand (diameter 0.25 - 0.1 mm) or coarser, including fragments up to 7.5 cm in diameter; 18 percent to 34 percent clay in the fine earth fraction.


    First identified near Holdrege, Nebraska and given the town’s name.

    silt loam

    Soil texture of the plow layer or comparable depth in virgin soil; in general, it is made up of less than 27 percent clay, 20 percent to 50 percent sand and 50 percent to 75 percent silt.


  • Soil Test
    Chemical analysis of soil samples to assess soil nutrient levels and determine how fertilizer use can be improved.
  • Soil Test Calibration
    A means of establishing a relationship between a given soil test value and the yield response from adding a nutrient to soil as fertilizer.
  • Soil Test Correlation
    The relationship between the amount of nutrient extracted from soil by a laboratory test and nutrient uptake by plants in the greenhouse or field and/or crop yield.
  • Soil Test P
    A measure of the availability of solution and labile soil P to a crop.
  • Soil Texture
    This refers to the relative proportions of sand, silt and clay in a soil.
  • Soil Water Content
    The water lost from the soil upon drying to a constant mass at 105 degrees C., expressed either as the mass of water per unit mass of dry soil or as the volume of water per unit bulk volume of soil. (1997. Soil Science Society of America. p. 103)
  • soils
    Soils are dynamic natural bodies having properties derived from the combined effect of climate and biotic activities (organisms), as modified by topography, acting on parent materials over periods of time. (Brady, N.C., and R.R. Weil. 2007. The Nature and Properties of Soils. Fourteenth Edition. Prentice Hall, Inc. Upper Saddle River, NJ. 980 pp.)
  • solid state reactions
    chemical reaction which proceeds without a solvent (i.e.,  water)

  • Solubility
    The ability of a solute to dissolve in a solvent; the ability of a herbicide to dissolve in water.
  • Soluble
    A state change when a solid material is put into a solvent. The molecules leave the solid phase and go into the liquid phase of the solvent
  • solum (plural: sola)
    A set of horizons that are related through the same cycle of pedogenic processes; the A, E, and B horizons.
  • Solute Molecules
    Molecules that are dissolved in a solvent
  • Solute Potential
    The effect of dissolved solutes on water potential.
  • Solution
    A liquid matrix where a solute has been dissolved in a solvent.
  • Solvent
    A liquid that is capable of dissolving other molecules called solutes. In biological systems, water is usually the solvent
  • Somatic Cells
    Body cells.
  • Sorption
    The removal of an ion or molecule from solution. Commonly used in regards to phosphorus fixation.
  • Southern Blot
    A method used to transfer DNA fragments separated during electrophoresis to membrane filters for detection of specific nucleotide sequences using probes.
  • Species

    A fundamental category of taxonomic classification, ranking below a genus or subgenus and consisting of related organisms capable of interbreeding.

  • SSR
    Simple Sequence Repeat, also known as a microsatellite. These DNA markers are based on differences in length of repeated di- and tri-nucleotide sequences. By identifying the conserved flanking sequences of these SSRs, primers can be designed to selectively amplify them via PCR. SSRs are usually codominant and a potentially large number can be identified. Only small amounts of DNA are required, and analyses can be run quickly and relatively inexpensively. However, initial identification of SSRs followed by design, synthesis, and evaluation of primers is a large-scale effort. Tautz (1989, Nucleic Acids Research 17:6463-6471) describes the biological basis of SSRs and their utility for genetic analysis. Roder et al. (1998, Genetics 149:2007-2023) reports on the development and mapping of microsatellites in wheat.
  • Stalk Rot
    One type of stalk rot, Anthracnose Stalk Rot, is caused by a fungus (Colletotrichum graminicola) that enters the corn plant above ground. The disease causes the inside of the stalk to degrade from bright white to gray. This disease weakens the stalk making it more likely for plants to lodge.
  • Staminode
    A stamen without anthers.
  • Starch
    Plant storage form of carbohydrate.
  • Start/Stop Codons
    Codons used to start and stop translation during protein synthesis.
  • Stems
    Bears the buds, leaves and flowers of a plant.
  • Stereochemically
    The specific 3-dimensional arrangement of atoms around an asymmetric carbon.
  • Sterility
    Unable to produce seed, pollen or spores capable of fertilization.
  • Stocking Density
    Animal demand per unit-area (AU/acre) at an instant in time.
  • Stoma
    Multiple stomata.  Minute pores in leaf surfaces defined by two guard cells that enable pores to open and close in response to changes in environmental conditions.
  • Stomata
    An opening in the outer layer cells in a leaf bordered by two guard cells and serving in gas exchange.
  • Stratification

    1. Exposing seeds to a cold period to encourange germination or break seed dormancy;

    2. Layering of plant material (herbacous, shrub, understory, canopy).

  • Stratified
    Exposed to a cold period to break seed dormancy.
  • Structure
    The combination or arrangement of soil particles that forms peds or aggregates.
  • STS
    Sequence Tagged Site. A DNA sequence of known location that occurs just once in the genome. STS loci are detectable by PCR, making them useful for a variety of molecular marker applications.
  • Style
    Part of the pistil (female reproductive structure) that transports the sperm collected by the stigma to the ovary for fertilization and developement of the egg; situated between the ovary and stigma
  • Substrate
    The substance, base, or nutrient on which an organism grows, (iii) Compounds or substances that are acted upon by enzymes or catalysts and changed to other compounds in the chemical reaction. (1997. Soil Science Society of America. p. 107)
  • Substrate Analogs
    Molecules that differ in structure, at one or more positions, from the endogenous substrate.
  • Suicide Substrate
    A substrate which irreversibly binds to the active site of an enzyme, causing it to be unable to catalyze further reactions.
  • Sulfonylureas
    A herbicide family with similar chemical structure belonging to the amino acid synthesis inhibitors mode of action; these herbicides specifically target the ALS-AHAS enzyme.
  • Superphosphoric Acid (0-79-0)
    A mixture of polyphosphate and orthophosphate made by dehydrating water from phosphoric acid; used to produce ammonium polyphosphate fertilizers.
  • Surface Creep
    The creeping of the surface.
  • Surfactant
    An additive that reduces the surface tension ofa herbicide to allow for better contact between water droplet and plant surface; cationic surfactants, ionic surfactants, nonionic surfactants; SURFace ACTive AgeNT.
  • Susceptibility
    A plant's inability to withstand a herbicide at normal use rates.  
  • Susceptible
    Sensitive to a stimulus.
  • Susceptible
    La incapacidad de una planta para sobrevivir a un herbicida aplicado a la dosis recomendada.
  • Suspension
    A solid dispersed in another solid, liquid or gas that does not dissolve but remains as a solid in the mixture.
  • Suspension
    The containment or support in fluid media (usually air or water) of soil particles or aggregates, allowing their transport in the fluid when it is flowing. In fluids at rest, suspension follows Stoke's Law. In wind this usually refers to particles or aggregates <0.1 mm diameter through the air, usually at a height of >15 cm above the soil surface, for relatively long distances.
  • Suspensor
    The organ anchoring and supporting a developing embryo. Suspensor connects embryo with its mother body.
  • sustainability
    Management of soil and crop cultural practices so as not to degrade or impair environmental quality on or off site, and without eventually reducing yield potential as a result of the chosen practice through exhaustion of either on-site resources or non-renewable inputs.
  • Symbiosis
    The living together of two or more biological entities.
  • Symplastic Path
    Water travels from one cell to the next via plasmodesmata. Symplastic means "living" tissue.
  • Synergism
    Increased phytotoxicity occurs when two or more chemicals are applied together, as compared to the individual chemicals applied alone.
  • Synergist
    A non-phytotoxic chemical which increases the phytotoxicity of a herbicide, usually by inhibiting metabolism of the herbicide through enzyme inhibition.
  • Systemic
    Having the ability to move throughout the plant by either the xylem or phloem.
  • Systemic Herbicide
    A herbicide that can move throughout the plant; the activity is not limited to the point of application.
  • Síntesis de Proteínas
    La producción de proteínas en una célula. Las proteínas son cadenas de aminoácidos unidos entre sí en un orden genéticamente determinado.
  • Taproot
    A main, deep-growing root that produces lateral roots.
  • Taq
    A DNA polymerase often used in PCR which can withstand high temperatures.
  • Taq Polymerase
    A DNA polymerase enzyme which is highly heat stable, used in PCR procedures.
  • Taqman
    A real time PCR probe detection system, using two labelled probes.
  • Target DNA
    The particular portion of the template DNA which is copied during PCR.
  • Taxonomy

    Orderly classification of plants and animals according to their presumed natural relationships.

  • Tepals

    A division of the perianth of a flower having a virtually indistinguishable calyx and corolla.

  • Terminal Moraines
    An accumulation of soil, pebbles, rocks, and boulders carried forward, deposited and marking the farthest advance of a glacier or ice sheet.
  • Terminal Tip
    On the end of a branch or stem.
  • Termination Sequence
    The sequence of DNA which signals the transcription to stop.
  • Terminator Genes
    A set of transgenes designed to arrest the final stages of seed development in a crop plant. The resulting trait is the production of seeds that will not germinate. Also called the technology protection system.
  • Terraces
    Physical earthen barriers to runoff and can be very effective in reducing P losses to erosion and runoff.
  • Tetrapirrol
    Una clase de moléculas caracterizadas por una serie de cuatro anillos, cada uno de los cuales está compuesto por cuatro átomos de carbono y uno de nitrógeno. Algunas moléculas que contienen tetrapirroles son los grupos hemo, las clorofilas, la vitamina B12 y el fitocromo.
  • Tetrapyrrole

    A class of molecules characterized by a series of four, five-membered rings containing four carbon atoms and one nitrogen. Tetrapyrrole molecules include hemes, chlorophylls, vitamin B12 and phytochrome.

  • Textural Class
    Classification of a soil based upon the relative proportions of sand, silt, and clay present. There are 12 textural classes listed here in order from coarsest to finest: sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, and clay.
  • textural triangle

    triangular soil identification guide with each side representing one of the soil separates (clay, silt or sand) and indicating the percentage of each in the soil. The intersection points of three lines from each side of the triangle determine how the soil texture will be classified. 

  • Texture
    The relative proportions of the various soil separates (i.e., sand, silt, clay) in a soil, as described by the classes of soil texture shown in Fig. 1.
  • Thermal Cycler
    The machine used in PCR which can be programmed for the heating and cooling cycles.
  • Thermophilic eubacterium
    Type of bacterium found in a hot environment.
  • Threonine
    Nonessential amino acid found in cheese, eggs, milk, meat, legumes, nuts and seeds.
  • Threshold Velocity
    Threshold velocity is the wind speed at which particle movement is initiated.
  • Thylakoid Membranes
    A series of sealed membrane compartments found inside the chloroplast of plant cells. The membranes contain the photosynthetic apparatus and all of the chlorophyll in the leaf. Their structure as closed 'sacks' permits functional 'inside' and 'outside' spaces within the chloroplast across which photophosphorylation can generate the proton gradient necessary for ATP synthesis.
  • Thyrse
    A type of inflorescence having 3 pairs of cymes in 3 verticillasters.
  • Ti Plasmid
    A circle of DNA found in Agrobacterium tumifaciens that encodes genes for moving the plasmid into a plant cell and inserting a portion of the plasmid into the plant chromosome.
  • Tilth
    The physical condition of soil as related to its ease of tillage, fitness as a seedbed, and its impedance to seedling emergence and root penetration.
  • Time
    One of the conventionally accepted soil forming factors.
  • Tissue Culture
    Plant cells are grown in culture which allows them to be manipulated and then induced to develop into whole plants.
  • Tolerance
    The inherent ability of a species to survive and reproduce after herbicide treatment; this implies that there was no selection or genetic manipulation to make the plant tolerant; it is naturally tolerant.
  • Tolerant
    The inherent ability of a plant to survive and reproduce after herbicide treatment. This implies that there was no selection or genetic manipulation to make the plant tolerant; it is naturally tolerant.
  • Tolerante
    La habilidad inherente de una planta para sobrevivir y reproducirse después de la aplicación de un herbicida. Esto implica que no ha habido una selección o manipulación genética para hacer a una planta tolerante; ésta es naturalmente tolerante.
  • Tonoplast
    The vacuolar membrane in plant cells.
  • Topography
    The combination of land slopes and the way those slopes interrelate.  Topography is one of the conventionally accepted soil forming factors.
  • Toposequence
    A sequence of related soils that differ, one from the other, primarily because of topography as a soil-formation factor. (SSSA)
  • Topt
    The optimum temperature for an enzymatic reaction.
  • Totipotency
    The capacity for a differentiated cell to develop into a whole plant.
  • Totipotency
    The ability of a single plant cell to grow, divide, and differentiate into an entire plant. Mammalian cells do not have this ability.
  • Totipotent
    The ability of a single plant cell to grow, divide, and differentiate into an entire plant. Mammalian cells do not have this ability.
  • Totipotente
    La capacidad de una sola célula para crecer, dividirse y diferenciarse en una planta completa. Las células de los mamíferos no presentan esta capacidad.
  • Tracheids
    One of the two major types of water-conducting cells found in plants (vessel elements are the others). The elongate cells are dead at maturity, have tapered ends and are arranged end to end and have walls that are partially coated with lignin.
  • Tracking Dye
    A dye molecule visible in room light that is mixed with a sample. This allows the scientist to track the loading of the sample and indicate it's movement through an electrophoresis gel.
  • Trade Name
    The name under which a product is marketed.
  • Trait
    The characteristic that results from an expressing gene(s). Ex. Upright leaves, drought tolerance, Bt resistance. A trait can be influenced by the environment.
  • Transcription
    The process by which the nucleotide sequence of DNA is copied into a single-stranded molecule of RNA. The nucleotide sequence of the RNA created is complementary to the DNA sequence except all thymine molecules are replaced with uracil molecules.
  • Transduce
    The process whereby a receptor initiates one or more sequences of biochemical reactions that connect the stimulus to a cellular response.
  • Transferencia de Electrones
    La transferencia de electrones entre una serie de componentes, de una manera controlada. Algunos ejemplos incluyen la cadena de transferencia de lectrones involucrada en la fosforilación oxidativa dentro de la mitocondria y la cadena de transferencia por medio de la cual se realiza la fotofosforilación en los cloroplastos. Los electrones son transferidos de moléculas con una alta energía libre a otras con menor energía libre.
  • Transformación
    El proceso por el cual material genético adicional es insertado en las células de un organismo.
  • Transformation
    A process by which extra genetic material is inserted into the cells of an individual.
  • Transformation
    The conversion from one chemical or mineralogical form to another.
  • Transformation
    A process by which extra genetic material is inserted into the cells of an individual.
  • Transforming
    The process of introducing foreign DNA into an organism which is then passed on to the organism’s progeny.
  • Transgene
    A gene that has been genetically altered. They are usually used to transform organisms. A foreign gene that has been inserted into the host's genomic DNA.
  • Transgenic
    An organism that has a new genetically engineered DNA sequence found in every one of its cells. Genetically engineered organisms are transgenic. These two terms are used interchangeably.
  • Transgenic Plant
    A plant that has a new genetically engineered DNA sequence present in every one of its cells. Genetically engineered plants are transgenic plants. These two terms are used interchangeably.
  • Transgressive Segregation
    Segregation of progeny phenotypes that are more extreme than either parent.
  • Transgénico
    Un organismo que en cada una de sus células contiene una nueva secuencia de ADN modificada por ingeniería genética. Los términos “transgénico” y “genéticamente modificado” son usados indistintamente.
  • Transit Peptide
    Special sequences found at the end of a protein to direct its transportation to the needed cellular location.
  • Translation
    The process following transcription during which the nucleotide sequence of mRNA is read and 'translated' into a chain of amino acids (protein). The mRNA sequence is read three nucleotides (codon) at a time, and each codon codes for a specific amino acid.
  • Translocation
    Movement of a substance, essentially without change, from one location to another.
  • Translocation
    The transport of herbicide short or long distances. Herbicides movement from site of application to site of action might involve cell to cell transport or long distance transport in the xylem or phloem.
  • Translocation
    Moving from one point to another within a plant by either the xylem or phloem.
  • Transmembrane Path
    The route followed by water that sequentially enters a cell on one side, exits the cell on the other side, enters the next in the series, and so on. In this path, water crosses at least two membranes for each cell in its path.
  • Transpiración
    La pérdida de agua en forma de vapor de la superficie de las plantas, principalmente a través de los estomas.
  • Transpiration
    The loss of water as vapor from plants at their surfaces, primarily through stomata.
  • Traqueidas
    Uno de los dos tipos principales de células conductoras de agua en las plantas (los elementos de los vasos son el otro tipo).  Estas células alargadas mueren en la madurez, tienen extremos adelgazados donde se unen unas a otras y presentan paredes parcialmente cubiertas con lignina.
  • Triazines
    A family of herbicides with similar chemical structure and belonging to the photosynthetic inhibitors mode of action.
  • Triglyceride
  • Triplet State
    A normally forbidden excited electron orbital that is reserved for an electron with the same spin as the electron remaining in the ground state. Upon excitation to an excited singlet state, there is some possibility that the electron will reverse spin. When this happens, the electron then drops down to the triplet state, which is at a lower energy level than the excited singlet state. Once in the triplet state, the electron must remain there until its spin is again reversed. Molecular oxygen is unusual in that it is normally in a triplet state.
  • Turbidity
    The amount of solid particles that are suspended in water and that cause light rays shining through the water to scatter. Thus, turbidity makes the water cloudy or even opaque in extreme cases. (USGS Water Science Glossary of Terms, 2004)
  • Turgencia
    La presión dentro de una célula como resultado de la absorción de agua.
  • Turgor
    Pressure within a cell resulting from the uptake of water.
  • Turgor Pressure
    The positive pressure built up when water is compressed.
  • Turnover Number
    The number of reactions per second that the enzyme can catalyze under optimum conditions.
  • Tyrosine
    nonessential amino acid
  • Umbel

    An indeterminate inflorescence, usually flat-topped with pedicels arising from a single point, like an umbrella.

    Armitage, A.;
    Herbaceous Perennial Plants


  • unavailable soil water

    soil water held so tightly to soil particles by adsorptive soil forces that it cannot be extracted by plants; remains present even when soil is drier than permanent wilting point.

  • Undifferentiated
    Cells that have not developed into specialized tissues. Undifferentiated cells, called callus, are used in tissue culture during the transformation process.
  • Universal Code
    The theory that the genetic code is used by all forms of life. This is what allows DNA from different organisms to be introduced into a new organism and function correctly.
  • Uptake
    The process of getting a herbicide from the outer surface of a plant to the inside of the plant where the herbicide will either induce its herbicidal activity or be translocated.
  • Urea
    A fertilizer type widely used in agricultural system to supply N. The average N content in urea is about 46%. Urea formula: (NH2)2CO
  • Urea (46-0-0)
    A dry nitrogen material produced by reacting ammonia with carbon dioxide.  Urea contains the highest percentage of nitrogen of the commonly used dry fertilizers and is rapidly replacing ammonium nitrate. When surface applied, urea is the most rapidly volatilized of the dry nitrogen materials.
  • Urea-Ammonium Nitrate (UAN)
    A nonpressure solution of ammonium nitrate, urea and water. Two grades are most common: 28-0-0 (10.7 lbs./gal.) and 32-0-0 (11.1 lbs./gal.).
  • Utilization
    The proportion of current year’s forage production that is consumed or destroyed by grazing animals.
  • Vacuola
    Un espacio dentro de la célula confinado por una membrana (el tonoplasto) que almacena materiales celulares ya sea disueltos en agua o en forma de masas cristalinas o floculentas.
  • Vacuolate Cell
    A cell derived from a progenitor cell during embryogenesis and having a large vacuole. Vacuolate cells usually are larger than cytoplasmic cells which result from the same cell division.
  • Vacuole
    A membrane-bound (tonoplast) space larger than a vesicle which stores material, either dissolved in water or as a crystalline or flocculent mass. Vacuoles are key organelles for storage of compounds and osmoregulation in plants.
  • Vadose Zone
    The zone of material between the surface and the water table.
  • Vapor
    Una sustancia en el estado gaseoso.
  • Vapor
    A substance in the gaseous state.
  • Variety
    Crop plants within a species that have the same genetic composition. Because plants in a variety are usually heterozygous, their offspring will not remain genetically pure (i.e., corn hybrid varieties).
  • Vascular Cambium
    A layer of meristematic cells located between xylem and phloem tissues which divide to give off cells toward both tissues. This process forms secondary growth in stems and roots in broadleaf plants.
  • Vasos
    Los elementos de los vasos.  Uno de los dos tipos principales de células conductoras de agua en las plantas (las traqueidas son el otro tipo).  Estas células alargadas mueren en la madurez, tienen extremos adelgazados donde se unen unas a otras y presentan paredes parcialmente cubiertas con lignina.
  • Vector
    A plasmid, virus, BAC or YAC used to carry a gene(s) of interest.
  • Vegetative

    growth stage where a plant produces new leaf tissue.

  • Vernalization

    Subjection of plants to low temperature in order to hasten plant flowering.

  • Verticillaster
    A false whorl of flowers.
  • Verticillate
    Arranged in whorls.  Armitage, A;
    Herbaceous Perennial Plants
  • Verticils
    A whorl of flowers or leaves.
  • Vessels
    Vessels, or vessel elements, are one of the two major types of water-conducting cells found in plants (tracheids are the others). The elongate cells are dead at maturity, have tapered ends and are arranged end to end and have walls that are partially coated with lignin
  • Viability
    The measure of the number of individuals in a given phenotypic class that survive relative to another class.
  • Vimeo

    A  United States-based video sharing website on which users can upload, share and view videos

  • Vm
    The limiting velocity of an enzymatic reaction. This would occur at an infinite substrate concentration.
  • Volatile
    Liquids or solids with relatively high vapor pressure at normal temperatures. The higher the vapor pressure, the more likely the substance will vaporize into a gas.
  • Volatility
    The ability of a compound to change from a liquid phase to its gaseous phase, dependant on chemical properties of compound and environmental conditions.
  • Volatilization
    The conversion of ammonium into ammonia gas. NH4 --------> NH3(gas)
  • Water Potential
    The chemical potential of water; a measure of the ability of a substance to absorb or release water relative to another substance.
  • water storage capacity

    amount of water that can be stored in a soil; storage capacity is determined by soil type and indicates the amount of water held in the soil. (See permanent wilting point.)

  • Water Table
    The upper surface of ground water or that level in the ground where the water is at atmospheric pressure. (SSSA)
  • Water-filled Porosity
    The percent of water occupying the empty spaces of soil and is inversely related to the percent of air occupying the empty spaces of soil. Total porosity= air-filled porosity plus water-filled porosity.
  • Water-holding Capacity
    The ability of a soil to hold water; varies by soil texture.  Medium textured soils--fine sandy loam, silt loam and silty clay loam--have the highest water holding capacity.
  • Water-holding Capacity
    The amount of water held in soil pores against the pull of gravity.
  • Water-holding Capacity
    The maximum amount of water a soil can hold against the pull of gravity.
  • Watershed
    The land area that drains water to a particular stream, river, or lake. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Large watersheds, like the Mississippi River basin contain thousands of smaller watersheds.
  • Wavelength
    The distance between equivalent positions in the electromagnetic wave formed by a photon as it moves through space. For visible photons, the wavelengths are in the range of 400 to 700 nm.
  • Weak Acid
    An organic acid which is incompletely inonized in aqueous solution.
  • Weak Base
    An organic base which is incompletely inonized in aqueous solution.
  • Weathering
    The means by which soil, rocks and minerals are changed by physical and chemical processes into other soil components.  Weathering is an integral part of soil development.
  • Weathering
    The complex combination of physical, chemical and biological processes that decompose, disintegrate and alter rocks and minerals at or near the Earth's surface. Weathering can be subdivided into chemical weathering, physical weathering, and biological weathering.  (Soil and Environmental Science Dictionary)
  • well-buffered
    having characteristics allowing resistance to change. In this case the abundance of calcite increases the soil’s ability to resist pH change for example.

  • Western Blot
    A technique in which proteins are separated using electrophoresis and transferred to a membrane so they can be identified and studied.
  • Wetland
    A transitional area between aquatic and terrestrial ecosystems that is inundated or saturated for long enough periods to produce hydric soils and support hydrophytic vegetation. (SSSA)
  • Wilting Point
    The moisture content of a soil at which most plants wilt.The wilting point is commonly estimated by measuring the 15-bar or 1.5 MPa percentage of a soil.
  • Xenobiotic
    Foreign chemicals; natural or synthetic substances that cannot be utilized by plants for energy-yielding processes.
  • Xilema
    Células especializadas de los tejidos vasculares de las plantas, que mueren en la madurez y que conducen agua y minerales.
  • Xylem
    Nonliving cells connected end to end to form a series of long, thin tubes from root to the shoot, used to supply cells with water and nutrients that are dissolved in water.
  • Yeast Two-Hybrid System
    A method for isolating pairs of proteins that interact via their DNA-binding and activation domains. Protein-protein interactions are commonly found in signal transduction cascades.

  • Yield Drag
    A negative effect on grain yield associated with crop plants that have a specific gene or a specific trait.
  • Yield Lag
    A relative reduction in yield observed in some hybrids or varieties compared with the yield observed in the most recently produced hybrids or varieties.
  • Yield Potential
    The highest yield a plant (hybrid, variety, etc.) is capable of producing when grown in ideal conditions.
  • Zinc Carbonate (52-56 percent zinc)
    Inorganic compounds that are very insoluble in water.  If granulated, zinc carbonate is not an effective source of zinc; however, it is effective if very finely ground.
  • Zinc Chelate (Zn-EDTA most common)
    Material blended with dry fertilizers and applied in a row band.  Granular zinc chelate is likely to be more effective than granular zinc sulfate because of its mobility.
  • Zinc Oxide (50-80 percent zinc)
    Inorganic compounds that are very insoluble in water.  Zinc oxide is not effective as a source of zinc if granulated, but is effective when finely ground.
  • Zinc Sulfate
    Relatively water-soluble inorganic compound.  The most commonly used dry zinc material.
  • Zwitterionic
    Having both a positive and negative charge.
  • Zygote
    The cell formed when the egg and sperm fuse. The cell has two copies of each chromosome (2n) and will continually divide to develop into an entire organism.

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