Fruit ripening in Vitis vinifera L.: possible relation of veraison to turgor and berry softening

Background and Aims: Vitis vinifera L. berries exhibit dynamic changes in water relations during development, but the possible connections between water relations, particularly cell turgor pressure (P), and ripening have received little attention, and the water relations have been studied by mostly indirect methods. Methods and Results: The cell pressure probe was utilized to examine directly the in situ P of cells in the mesocarp. Mesocarp cell P demonstrated a consistent pattern of a high value early in development, followed by a decrease to less than 1.0 bar that was maintained during ripening. Sugar accumulation did not increase significantly until P had declined to less than 1.0 bar. Fruit 'elasticity' was used to evaluate fruit firmness during development. Fruit elasticity changed dynamically and synchronously with P. When growth was prevented with plastic boxes, the decline in cell P was delayed over 14 days, and the onset of skin colour and sugar accumulation was similarly delayed. Conclusions: The results show that when the decrease in P was delayed, the onset of ripening was delayed, and, therefore, are consistent with a central role of P in the onset of ripening. Significance of the Study: This study showed that boxing preveraison berries similarly delayed P decrease and colour increase in Cabernet Sauvignon berries. Thus, this system may be useful to study the relationship between P and gene expression in developing berries.