Changes in Polygalacturonase Activity and Calcium Content during Ripening of Grape Berries

Abstract

Changes occurring in the cell walls of grape berries during ripening may contribute to berry softening. Pectic substances are mainly responsible for cell wall cohesion in association with calcium ions. We measured the activity of the pectin hydrolyzing enzyme, polygalacturonase, during the development of Sauvignon blanc and Semillon grape berries. Although absent during herbaceous growth, polygalacturonase activity increased during ripening. Levels were higher in Semillon than in Sauvignon blanc ripe berries. No significant differences were found between skin and flesh polygalacturonase activity in ripe Sauvignon blanc grape berries. During ripening, the calcium content of Sauvignon blanc grape berries decreased. The calcium content of the skin was higher than in the flesh of ripe Semillon and Sauvignon blanc berries. Levels were higher in Sauvignon blanc than in Semillon whole ripe berries. In all cases and in both cultivars, polygalacturonase activity and calcium content were diametrically opposed. Moreover, polygalacturonase activity in ripe berries was inhibited, in vitro, by 1 mM or more of calcium ion. Polygalacturonase activity seems to increase with the degree of maturity and with the decrease of calcium content.