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

To study the role of abscisic acid (ABA) and gibberellins (GA) in pre-maturity a-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 ( 3 H-ABA) and gibberellic acid ( 3 H-GA 3 ) were diluted with unlabelled ABA (100 mM) and GA 3 (50 mM), 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 a-amylase activity. This confirmed that exogenously applied ABA and GA were absorbed in sufficient amounts to alter grain metabolism and impact on PMA. E xogenous hormone application is an important experimental technique for helping to understand the hormonal control of plant growth and development. Different methods have been used to study the effects of exogenous hormones on grain development. A few studies have dealt with pre-anthesis hormone regulation of floret development 31 , whereas most studies investigated grain development after anthesis 22 . Generally in cereals, abscisic acid (ABA) and gibberellic acid (GA 3 ) solutions have been applied separately either by spraying onto the leaves and spikes 1,7,31-32 or by injecting into the leaf sheath 31 to study their role in floret development, grain set and filling. Yang et al. 32 applied ABA (20 mM) by spraying the leaves and panicles in two rice cultivars, Wuyujing 3 and Yangdao 4, daily for 7 days starting at 9 days after anthesis (DAA), and observed a 3-to 4-fold increase in ABA levels in grains at 12 and 20 DAA in ABA-treated plants compared to plants treated with water in both cultivars. Similar results were reported later by , after spraying ABA (20 mM) solution onto the panicles of rice plants daily for 8 days starting at the initiation of heading, and ABA levels in grains were measured at 9 and 16 DAA. They observed that an increase in the endogenous ABA levels in grains was about 4-fold at 9 DAA and 2-fold at 16 DAA in ABA-treated plants compared to plants treated with water. In both studies, ABA was quantified by the enzyme-linked immunosorbent assay (ELISA) using mouse monoclonal antibodies against ABA. This shows that a substantial amount of applied ABA reaches the grain in a biological active form. The role of ABA and gibberellins (GA) in regulating a-amylase formation in germinating and pre-harvest sprouted wheat grains is well documented in the literature . However, their role in regulating pre-maturity a-amylase (PMA) synthesis in intact, developing wheat grains is less well known. In order to determine the role of ABA and GA in a-amylase formation in developing grains, it is necessary to investigate the most effective method for in situ hormone application to ensure that the applied hormones are being taken up by the grains.