Aspects of grape berry development bioenergetics

Since the typical evolution of solutes occurring during berry development was not explained by the evolution of soluble enzymes, we have tested the hypothesis that it should be governed by compartmentation. As expected from the absence of increase in respiration in grapevine, cytochrome c oxydase activity kept constant after veraison. However, the climacteric rise in respiration was replaced by the induction of alcool dehydrogenase. Two vacuolar proton pumps created a positive membrane potential resulting in the accumulation of organic acids inside the vacuole. PPase was threefold more active than V-ATPase. The activity of both HC pumps increased in parallel during the period of sugar storage, while malic acid content decreased. The activity of plasma membrane ATPase, a possible marker for the apoplastic loading of sugars, was fixed as soon as four weeks before softening, and kept constant during ripening. However, the onset of ripening was accompanied by an increase of the expression of cDNA homologous to hexoses and sucrose carriers. These results suggest that malate breakdown, following its vacuolar decompartmentation, could be a consequence of a decrease in the energy available for its storage or of an increase in vacuolar conductance during ripening.