ABSCISIC-ACID ACCUMULATION IN LEAVES AND CULTURED-CELLS DURING HEAT ACCLIMATION IN GRAPES

Heat tolerance and endogenous ABA levels in leaves and cultured grape cells (Vitis spp., cultivars Venus and Veeblanc) were evaluated during heat acclimation. Plants and cultured cells were acclimated at 38 and 36C, respectively. Heat tolerance increased rapidly after exposing plants or cells to acclimation temperatures, reaching a maximum after 10 to 16 hours and 10 to 12 hours for leaves and cultured cells, respectively. Free and bound ABA levels increased sharply during the first hour of heat acclimation, before leaves and cultured cells reached their maximum heat tolerance. The increase in ABA during heat acclimation was 2- to 3-fold that of the nonacclimated control, and the time of the ABA accumulation peak in tissue roughly corresponded to the maximum heat tolerance in leaves and cultured cells. Heat tolerance was induced in cultured cells by exogenous ABA application. Heat tolerance increased significantly after 24 hours of ABA application at 7.6 or 9.5 gm. The results suggest that ABA may be a factor in high-temperature acclimation and heat-tolerance induction in grapes. Chemical name used: abscisic acid (ABA).