Quantifying the impact of exogenous abscisic acid and gibberellins on pre-maturity α-amylase formation in developing wheat grains

To study the role of abscisic acid (ABA) and gibberellins (GA) in pre-maturity alpha-amylase (PMA) formation in developing wheat grain, two glasshouse experiments were conducted under controlled conditions in the highly PMA-susceptible genotype Rialto. The first, determined the relative efficacy of applying hormone solutions by injection into the peduncle compared to direct application to the intact grain. The second, examined the effects of each hormone, applied by either method, at mid-grain development on PMA in mature grains. In the first experiment, tritiated ABA (H-3-ABA) and gibberellic acid (H-3-GA(3)) were diluted with unlabelled ABA (100 mu M) and GA(3) (50 mu M), respectively, and applied at mid-grain development using both methods. Spikes were harvested after 24, 48 and 72 h from application, and hormone taken up by grains was determined. After 72 h, the uptake per grain in terms of hormones applied was approximately 13% for ABA and 8% for GA(3) when applied onto the grains, and approximately 17% for ABA and 5% for GA(3) when applied by injection. In the second experiment, applied ABA reduced, whereas applied GA(3) increased alpha-amylase activity. This confirmed that exogenously applied ABA and GA were absorbed in sufficient amounts to alter grain metabolism and impact on PMA.