Invertase activity, grape berry development and cell compartmentation

The effect of gibberellic acid on grape (Vitis vinifera L. cv. Sultanina) g rowth, beta-fructofuranosidase (EC 3.2.1.26) activity and carbohydrate leve ls was investigated throughout berry development and ripening. Although the fruits responded to hormone application with the expected increase in size , growth was not correlated with enzymic activity and hexose accumulation. This suggests that there is no direct regulatory relationship between inver tase and the rate of assimilate import. However, fructose:glucose ratios ch anged from 0.1 in green berries to 1.0 in mature samples. The latter situat ion can be reconciled with the 1:1 stoichiometry of sucrolysis by invertase . It is suggested that this is attributable to a spatial separation of subs trate and enzyme in green tissue. Compartmentation studies indicate that me socarp cell integrity gradually deteriorates during ripening, which allows invertase to leak out of the vacuole into the surrounding tissue. In fact, the protein fraction retrieved from a buffered medium after incubation of r ipening berry slices contained a soluble invertase of presumably vacuolar o rigin with an acid pH-activity profile and a pI of about 4. (C) Elsevier, P aris.