Possible role of soluble invertase in the gibberellic acid berry-sizing effect in Sultana grape

It is well known that post-bloom applications of gibberellic acid (GA(3)) increase seedless grape berry size by enhancing cell division, or cell enlargement, or both. As a consequence, total water and sugar per berry are increased. Soluble invertase is considered to be one of the key enzymes in the accumulation of sugar in grape berries. To study a possible role of invertase in the GA(3) berry-sizing effect, different rates of post-bloom GA(3) were applied to seedless grape cv. Sultana and hexose concentration and invertase activity were measured. GA(3) stimulated both parameters as early as 24 and 32 h after applications, respectively. Moreover, the increment in sugar content and enzyme activity remained throughout the growing of the berries period and, at ripening, increases in hexoses content (102%) and invertase activity (60%) were detected when GA(3) was applied at a rate of 45 ppm. At the same GA(3) rate the pericarp cells doubled in size. Furthermore, positive correlations were found between berry-size, invertase activity and hexose content, suggesting that GA(3) stimulation of invertase could be one of the factors involved in the berry sizing-effect of GA(3).