QUANTITATIVE AND QUALITATIVE DIFFERENCES IN C-6-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 act ion of hydroperoxide lyase (HPL), a component of the lipoxygenase (LOX ) pathway and form the basis of the ''green-note'' flavour characteris tic of many consumed plant products. Arabidopsis leaf tissue contains the C-6-aldehydes hexanal, and trans-2-hexenal as well as the C-6-alco hols: hexanol, and 3-hexenol. Interconversion between C-6-aldehydes an d alcohols is thought to proceed through the action of alcohol dehydro genase (ADH). Using an ADH mutant of Arabidopsis, we have shown that t here are large quantitative and qualitative differences in the accumul ation of C-6-volatiles in the absence of ADH activity. The total quant ity of LOX-derived volatiles is greater on a fresh weight basis in the ADH mutant. Qualitatively, hexanol and 3-hexenol levels are approxima tely 62% and 51% lower in the mutant, respectively, whereas levels of hexenal are approximately 10-fold higher. Hexanal accumulation, howeve r, is unaffected in the mutant. The altered profile of LOX-derived vol atiles does not have an effect on the steady-state levels of mRNA for allene oxide synthase (AOS) or LOX. HPL activity and mRNA quantity, ho wever, are higher in the mutant relative to wild type, suggesting that altered product levels in the mutant affect HPL regulation.