Invertase activity, grape berry development and cell compartmentation |
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Authors: | Luc P. Dreier Jacobus J. Hunter Hans Peter Ruffner |
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Affiliation: | 1Institute of Plant Biology, University of Zürich, Zollikerstr. 107, CH-8008 Zürich, Switzerland;2ARC-Fruit, Vine and Wine Research Institute, Nietvoorbij Centre for Vine and Wine, Private Bag X5026, 7599 Stellenbosch, Republic of South Africa;3Swiss Federal Research Station for Fruit-Growing, Viticulture and Horticulture, CH-8820 Wädenswil, Switzerland |
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Abstract: | The effect of gibberellic acid on grape (Vitis vinifera L., ev. Sultanina) growth, β-fructofuranosidase (EC 3.2.1.26) activity and carbohydrate levels 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 invertase and the rate of assimilate import. However, fructose:glucose ratios changed from 0.1 in green berries to 1.0 in mature samples. The latter situation can be reconciled with the 1:1 stoichiometry of sucrolysis by invertase. It is suggested that this is attributable to a spatial separation of substrate and enzyme in green tissue. Compartmentation studies indicate that mesocarp 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 ripening berry slices contained a soluble invertase of presumably vacuolar origin with an acid pH-activity profile and a pI of about 4. |
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Keywords: | Cellular localisation invertase ripening Vitis vinifera |
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