Changes in leaf phenolic compounds in two grapevine varieties (Vitis vinifera L.) grown in different water conditions

In 2004 growing season, at the experimental vineyard of the DCDSL of the Pisa University, located at Colignola (Pisa, Italy), two grapevine genotypes, ‘Cabernet Sauvignon’ and ‘Sangiovese’, were subjected to different water treatments (irrigated and non irrigated) under field conditions. Time-course measurements of pre-dawn leaf water potential, as well as of both leaf gas exchange performance and net carbon gain were conducted. Changes in the content and composition of leaf polyphenols were also evaluated. Identification and quantification of hydroxycinnamates and flavonoid glycosides were performed using both HPLC-DAD and HPLC-MS analyses. We show that the share of newly assimilated carbon for the synthesis of phenylpropanoids increased because of moderate water deficit. The flavonoid to hydroxycinnamate ratio markedly increased passing from well-watered to drought-stressed plants, while the quercetin to kaempferol ratio slightly increased because of drought stress. We argue that the tested genotypes did not actually suffer from a severe oxidative damage under the attempt to impose a drought stress.