Quantitative and qualitative differences in C6-volatile production from the lipoxygenase pathway in an alcohol dehydrogenase mutant of Arabidopsis thaliana

Six-carbon (C-6) volatile products are released from the enzymatic action of hydroperoxide lyase (HPL), a component of the lipoxygenase (LOX) pathway and form the basis of the "green-note" flavour characteristic of many consumed plant products. Arabidopsis leaf tissue contains the C-6-aldehydes hexanal, and trans-2-hexenal as well as the C-6-alcohols: hexanol, and 3-hexenol. Interconversion between C-6-aldehydes and alcohols is thought to proceed through the action of alcohol dehydrogenase (ADH). Using an ADH mutant of Arabidopsis, we have shown that there are large quantitative and qualitative differences in the accumulation of C-6-volatiles in the absence of ADH activity. The total quantity of LOX-derived volatiles is greater on a fresh weight basis in the ADH mutant. Qualitatively, hexanol and 3-hexenol levels are approximately 62% and 51% lower in the mutant, respectively, whereas levels of hexenal are approximately 10-fold higher. Hexanal accumulation, however, is unaffected in the mutant. The altered profile of LOX-derived volatiles does not have an effect on the steady-state levels of mRNA for allene oxide synthase (AOS) or LOX. HPL activity and mRNA quantity, however, are higher in the mutant relative to wild type, suggesting that altered product levels in the mutant affect HPL regulation.