COORDINATE ACCUMULATION OF ANTIFUNGAL PROTEINS AND HEXOSES CONSTITUTES A DEVELOPMENTALLY CONTROLLED DEFENSE RESPONSE DURING FRUIT RIPENING IN GRAPE

During ripening of grape (Vitis labruscana L. cv Concord) berries, abu ndance of several proteins increased, coordinately with hexoses, to th e extent that these became the predominant proteins in the ovary. Thes e proteins have been identified by N-terminal amino acid-sequence anal ysis and/or function to be a thaumatin-like protein (grape osmotin), a lipid-transfer protein, and a basic and an acidic chitinase. The basi c chitinase and grape osmotin exhibited activities against the princip al grape fungal pathogens Guignardia bidwellii and Botrytis cinerea ba sed on in vitro growth assays. The growth-inhibiting activity of the a ntifungal proteins was substantial at levels comparable to those that accumulate in the ripening fruit, and these activities were enhanced b y as much as 70% in the presence of 1 M glucose, a physiological hexos e concentration in berries. The simultaneous accumulation of the antif ungal proteins and sugars during berry ripening was correlated with th e characteristic development of pathogen resistance that occurs in fru its during ripening. Taken together, accumulation of these proteins, i n combination with sugars, appears to constitute a novel, developmenta lly regulated defense mechanism against phytopathogens in the maturing fruit.