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The role of JAR1 in insect feeding response

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Experiment 2: Insect Response

The magnitude of plant response to wounding by leaf crushing was different from insect feeding. JA-Ile synthesis is much higher in crushed plants, for both the WT and the jar1 mutant.

Table 2. JA-Ile levels (pmole g - 1) after leaf crushing and cabbage looper feeding
Time sample collected WT crushing jar1 crushing WT with insect feeding jar1 with insect feeding WT unwounded (No feeding) jar1 unwounded (No feeding)
0 min. 0 0 17 1 1 1
60 min. 275 25 37 3 1 1
120 min. 200 25 7 2 1 1

Is it possible that this lower response level in the plants to insect wounding still allows the plants to mount some sort of defense against the cabbage loopers to slow down their feeding?  Would there be a difference between the WT and the jar1 mutant in their insect defense?  These questions were answered when Scott conducted the insect response experiment.

The second experiment focused on the insect response to the two types of Arabidopsis plants. If JAR1 signals help the Arabidopsis plants mount a defense, the cabbage loopers might feed less on the normal (wild-type) compared with the mutant plants. This experiment required a 3-day feeding time. Scott weighed all the cabbage loopers, let some feed exclusively on wild-type plants, let others feed exclusively on jar1 mutants, and reweighed them after 3 days. Because some insects ate more than others, he averaged all the initial and final weights for both plant treatment types and then calculated their changes in weight as a percentage.

Because Scott placed the cabbage loopers on islands of plants surrounded by water, he created an environment that gave the cabbage loopers only one feeding choice. As Scott monitored the experiment he could predict that the functioning of the JAR1 gene in the wild-type plants would not dramatically repel these insects. There was not a mass escape attempt of cabbage loopers from the wild-type or the jar1 plants.  The impact would be measured in the weight changes of these insects after the three day feeding.



Question 12: Which of the statements below is supported by the results of this experiment?

A. The cabbage loopers did not like to eat the Arabidopsis plants, so they lost weight during the three day study.
B. The cabbage loopers will eat both the wild-type and jar1 plants, but they gain less weight eating the wild-type, either because they eat less of it or because they are less able to assimilate its nutritive value.
C. The gene altered in the jar1 mutant does not have an influence on the cabbage looper insects as they feed on these plants.

Because Scott was a part of a research team using Arabidopsis as the model plant subject in their experiments, they could take advantage of the previous discoveries of other mutants known to impact JA response.  One mutant, coi1, was available to Scott to repeat the insect response experiment. This provided a comparison of cabbage looper weight gain on wild-type plants that had no mutant genes, jar1 plants, and coi1 plants.


Question 13:  Based on the results of the insect response experiment using the mutant coi1, select the best conclusion.

A. The COI1 gene does not influence cabbage looper weight gain.
B. The COI1 gene must be responsible for the JA response, not the JAR1 gene.
C. The COI1 gene has a stronger influence on cabbage looper weight gain than the JAR1 gene, but both impact the cabbage looper weight gain.



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