Effects of exogenous abscisic acid and gibberellic acid on pre-maturity α-amylase formation in wheat grains

Effects of in situ and in vitro applied abscisic acid (ABA) and gibberellic acid (GA(3)) on pre-maturity alpha-amylase (PMA) were investigated in glasshouse experiments under cool-temperature shock-induced and non-induced conditions using UK winter wheat varieties, Spark (low PMA susceptible) and Rialto (high PMA susceptible). In the in situ study, hormone solutions (ABA [100 mu M], GA(3) [50 mu M] and ABA + GA(3) [100 + 50 mu M]) were applied during mid-grain development to intact, developing grains of induced and non-induced plants. Alpha-amylase activity was measured in embryoless half-grains at maturity by a modified Phadebas assay. In the in situ study under non-induced conditions, applied ABA had no significant effect on alpha-amylase in either variety whereas applied GA(3) significantly increased alpha-amylase in Rialto, but not in Spark. In the in situ study under induced conditions, applied ABA and GA(3) produced no significant effect on alpha-amylase in Spark; however in Rialto, applied ABA produced a small but significant decrease in alpha-amylase whereas GA(3) significantly increased alpha-amylase under induced conditions. In the in vitro study, spikes were harvested from induced/non-induced plants at 44/40 days after anthesis. Embryoless half-grains were incubated in hormone solutions at 25 degrees C and alpha-amylase activity was measured. Results similar to the in situ study were observed in the in vitro study for both varieties and conditions, except GA(3) treatment which significantly increased alpha-amylase under non-induced conditions in Spark. From these exogenous hormone studies, it appears that GA-response is a major factor during PMA induction by a cool-temperature shock whereas ABA-response seems to be of less importance.