Effects of genetic manipulation of alcohol dehydrogenase levels on the response to stress and the synthesis of secondary metabolites in grapevine leaves.

The functional role of Adh in regulating susceptibility to abiotic stress and the synthesis of secondary metabolites was investigated in transgenic grapevine plants over- and underexpressing alcohol dehydrogenase (Adh). Plants were transformed with gene constructs containing a sense or antisense orientated grapevine VvAdh2 cDNA under the constitutive cauliflower mosaic virus 35S promoter. Plants transformed with either antisense orientation or the Adh-less construct displayed a low but detectable constitutive ADH activity, whereas plants transformed with the sense-expressed transgene showed a significantly higher (100-fold) ADH activity than the control. Compared with the control, the sense transgene induced an overexpression of VvAdh2 transcripts, whereas a reduced VvAdh2 expression was detected in antisense transformants. Grapevine plants overexpressing Adh displayed a lower sucrose content, a higher degree of polymerization of proanthocyanidins, and a generally increased content of volatile compounds, mainly in carotenoid- and shikimate-derived volatiles. In general, no significant differences between sense/antisense transformants were observed with regard to carotenoid and chlorophyll contents, suggesting a strong metabolic regulation of the synthesis of these compounds.