GIBBERELLIC-ACID STIMULATION OF ISOPEROXIDASE FROM PEDICEL OF GRAPE

Soluble peroxidase activity from pedicels of cv. Thompson seedless gra pe was highly stimulated by post-bloom gibberellic acid (GA(3)) applic ations to vines. This stimulation was dependent on the dose employed a nd increased with berry ripening. In control vines, i.e. non GA(3) tre ated, the level of peroxidase activity remained constant during; berry ripening. Isoelectrofocusing (IEF) analysis of soluble peroxidases fr om pedicel extracts performed ina 3-10 pH range, showed the presence o f a main band that corresponded to an acidic isoperoxidase of (pI 3.5) and the presence of a minor band of (pI 3.9). It is a well-known fact that GA, applications to cv. Thompson seedless grape beside producing berry enlargement cause berry-drop which has been associated with ped icel thickening. Here we found a positive correlation between pedicel thickness and peroxidase activity within the rates of GA, used. The in volvement of the acidic isoperoxidases in pedicel thickening and its r elation to berry-drop are discussed. (C) 1998 Elsevier Science Ltd. Al l rights reserved.