Injury to a leaf and the chemicals it produces

In looking for discussions of the consequences of damage on leaf volatile production—the aromatic compounds produced when leaves are damaged, came across an experiment that detailed what the intact parts of a leaf does when the leaf sustains partial damage.*

Matsui and colleagues injured Arabidopsis leaves. Arabidopsis thaliana is a favorite research plant, because it grows quickly, and because it is the first plant for which the complete genome was sequenced.

Arabidopsis thaliana, from Wikipedia

The injured part of the leaf produced a chemical, (Z)-3-hexenal. The plant produces this chemical to decrease the chances of further attack, because it is insecticidal, bacteriocidal, and fungicidal. However, this chemical can also be toxic to the plant itself. 

The question is, then, what does the uninjured part of the leaf do with (Z)-3-hexenal that reaches it. It turns out that the leaf converts the chemical into non-toxic products, (Z)-3-hexenol and (Z)-3-hexenyl acetate. As shown in the diagram below (from the article), this conversion requires an enzyme, aldehyde reductase, and a chemical called NADPH (green oval). The production of NADPH for this reaction requires energy and intact cells, so can only be carried out by the uninjured part of the plant. 

Meanwhile, as you can see in the diagram (red oval), enzymes in the injured part of the plant spontaneously transform (Z)-3-hexenal into (E)-2-hexenal, and, with oxygen from the air (red circle), into at least three other compounds. No energy is needed for these steps, so they occur spontaneously when cell compartments are broken down and enzymes are released.

In the “You can’t win” department: the non-toxic products are released into the air and attract many different predatory insects that proceed to destroy the injured plant...

Why the interest in this question? (E)-2-hexenal is one of the chemicals one of the chemicals that gives the smell to new-mown grass, and one of the chemicals that are produced in the tea leaf after plucking and during withering, and one of the chemicals we humans appreciate in the flavor of green tea!

* Matsui K, Sugimoto K, Mano J, Ozawa R, Takabayashi J (2012) Differential Metabolisms of Green Leaf Volatiles in Injured and Intact Parts of a Wounded Leaf Meet Distinct Ecophysiological Requirements. PLoS ONE 7(4): e36433. doi:10.1371/journal.pone.0036433