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 signaling, in both abiotic (crushing or cutting) and biotic (cabbage looper) stress response.

Figure 5. Options for how jasmonoyl isoleucine is created. Notice the chemical structures and the labels of inactive and active signaling compound below the structures. Only one image is correctly designed.

Option A - JAR1 converts inactive signaling compound (jasmonic acid) plus isoleucine to the active signaling compound (Jasmonoyl isoleucine)

Option B - JAR1 converts the active signaling compound (jasmonic acid) plus isoleucine to the inactive signaling compound (Jasmonoyl isoleucine)

Option C - JAR1 converts the inactive signaling compound (jasmonic acid) to isoleucine and the active signaling compound (Jasmonoyl isoleucine)

Option D - JAR1 converts the inactive signaling compound (Jasmonoyl isoleucine) to isoleucine and the active signaling compound (jasmonic acid)

Option E - JAR1 converts active signaling compound (Jasmonoyl isoleucine) to isoleucine and inactive signaling compound (jasmonic acid)

Quiz

Question

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 Fragrant Signals 1 video, which of the choices Figure 5 correctly illustrates the pathway leading to defense-related gene expression that occurs when the plant is wounded?

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.

Sorry. Your answer is not fully correct. It is true that the first compound is jasmonic acid, but, with respect to the wound-response pathway, it is an inactive, not active, signaling compound. It is also true that 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 does yield the final signaling compound, JA-isoleucine, shown as the last compound, but Scott said JA-isoleucine was determined to be the active, not inactive, signaling compound in the wound-response pathway.

Looks Good! 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 experiments to test this hypothesis.

Previous Page Next Page