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

It is well known that post-bloom applications ofgibberellic acid (GA3) increase seedless grapeberry size by enhancing cell division, or cellenlargement, or both. As a consequence, total waterand sugar per berry are increased. Soluble invertaseis considered to be one of the key enzymes in theaccumulation of sugar in grape berries. To study apossible role of invertase in the GA3berry-sizing effect, different rates of post-bloomGA3 were applied to seedless grape cv. Sultanaand hexose concentration and invertase activity weremeasured. GA3 stimulated both parameters as earlyas 24 and 32 h after applications, respectively.Moreover, the increment in sugar content and enzymeactivity remained throughout the growing of the berries period and, at ripening, increases in hexosescontent (102%) and invertase activity (60%) weredetected when GA3 was applied at a rate of 45 ppm.At the same GA3 rate the pericarp cellsdoubled in size. Furthermore, positive correlationswere found between berry-size, invertase activity andhexose content, suggesting that GA3 stimulationof invertase could be one of the factors involved in theberry sizing-effect of GA3.