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)) i ncrease seedless grape berry size by enhancing cell division, or cell enlar gement, or both. As a consequence, total water and sugar per berry are incr eased. 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 inverta se in the GA(3) berry-sizing effect, different rates of post-bloom GA(3) we re applied to seedless grape cv. Sultana and hexose concentration and inver tase activity were measured. GA(3) stimulated both parameters as early as 2 4 and 32 h after applications, respectively. Moreover, the increment in sug ar content and enzyme activity remained throughout the growing of the berri es period and, at ripening, increases in hexoses content (102%) and inverta se 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, po sitive correlations were found between berry-size, invertase activity and h exose content, suggesting that GA(3) stimulation of invertase could be one of the factors involved in the berry sizing-effect of GA(3).