Thaumatin-like proteins and chitinases, the haze-forming proteins of wine,accumulate during ripening of grape (Vitis vinifera) berries and drought stress does not affect the final levels per berry at maturity

Thaumatin-like proteins and chitinases, which are pathogenesis-related (PR) proteins, were the major soluble protein components of grapes from five cu ltivars of Vitis vinifera. This dominance of PR proteins was apparent at be rry softening ( veraison) and then throughout berry development for the Mus cat of Alexandria, Sultana, and Shiraz cultivars and in the berries of the Sauvignon Blanc and Pinot Noir cultivars examined at commercial maturity. T he M-r of the major thaumatin-like protein from Muscat of Alexandria grapes was 21 272, and those of the three major chitinases from this cultivar, Ch itB, ChitC, and ChitD, were 25 588, 25 410, and 25 457, respectively. The v ines in the study were irrigated and showed no obvious signs of disease. Sh iraz vines that had not been irrigated throughout the season were clearly w ater stressed, but had levels of PR proteins in the berry similar to vines that had been fully irrigated. It appears that the production of PR protein s that cause protein instability in wines by grapes may be Little influence d by environmental conditions.