Previous Discovery

The discovery process in science often reveals surprising results. Dr. Staswick and his team had spent years following the clues from well-conducted experiments that revealed the biological role of jasmonic acid and the plant genes that regulate its signal-inducing capacity.  Clues from studies by the Staswick team and other research groups implicated jasmonic acid signalling, in both abiotic (crushing or cutting) and biotic (cabbage looper) stress response.

chemical reactions of JAR1



Dr. Staswick discovered that the JAR1 enzyme was involved in the Arabidopsis plant’s response to wounding. Based on what you have learned in the video, which of the choices in the above figure correctly illustrates the pathway leading to defense-related gene expression that occurs when the plant is wounded?

Looks Good! Correct: Good job! The first compound is jasmonic acid, which, with respect to the wound-response pathway, is the inactive signaling compound. Together with the amino acid isoleucine, the second compound shown, the two are conjugated (joined) together in a reaction catalyzed by the enzyme JAR1. This yields the final signaling compound, JA-isoleucine, is shown as the last compound, which Scott said was determined to be the active signaling compound in the wound-response pathway.

Prior to Scott’s experiment with the Arabidopsis plants and hungry cabbage loopers, the team conducted experiments with wild-type and jar1 plants that had been wounded by mechanically cutting or crushing a leaf or petiole. The Staswick lab used a reliable method for measuring the amount of JA-Isoleucine (JA-Ile); this is indicative of the amount of JA that was bound to the amino acid isoleucine. Therefore, they could measure the quantity of JA-Ile in the plant in response to the wounding treatment. 

The working hypothesis of the research team was that making JA-Ile was a key step in the response pathway that allowed plants to mount a defense against feeding insects.  Scott's assignment was to plan and conduct exeperiments to test this hypothesis.