Differential rates of α-amylase and acid phosphatase induction by Ga 3 in embryoless half-seeds and isolated aleurones of wheat

Abstract

The induction of α-amylase and acid phosphatase by gibberellic acid (GA 3) was significantly higher (2–4-fold) in embryoless half-seeds of wheat than that observed in the excised aleurones. Addition of endosperm extract to excised aleurones enhanced the stimulatory effect of GA 3 on amylase activity by approximately 2-fold. Substitution of endosperm extract by 19 amino acids in GA 3-treated aleurones also brought about a 2–2.5-fold stimulation of α-amylase activity. Subsequent studies revealed that the addition of seven non-polar amino acids (0.5 mM each) was sufficient for the enhanced induction of α-amylase (1.8–2.5-fold) in GA 3-treated aleurones. A similatory effect of endosperm extract and amino acids on acid phosphatase activity was observed in GA 3-treated wheat aleurones. These observations are of physiological significance since an increased pool of free amino acids (5-fold) was also witnessed in the incubation medium of GA 3-treated half-seeds in comparison to the hormone-treated aleurones. The relative abundance of free amino acids in half-seed seems vital for the maximal induction of α-amylase and acid phosphatase. Thus, the presence of endosperm tissue associated with the aleurone layers is crucial for enhanced rate of production of GA 3-induced α-amylase and acid phosphatase in the wheat system.