Hormonal and Genetic Regulation of α-Amylase Synthesis in Barley Aleurone Cells

Abstract

The production and secretion of α-amylase and several other hydrolases by the aleurone cells of germinating barley seeds are regulated by two hormones, gibberellic acid (GA₃) and abscisic acid (ABA) (16,18). While GA₃ enhances the production of α-amylase, ABA is able to reverse the GA₃ effect. Yet, these two hormones do not directly compete with each other and they appear to have different mode of action (1,7). It has been demonstrated unequivocally that the GA₃ enhancement on α-amylase production is essentially due to the de novo synthesis of α-amylase molecules (3,8). The GA₃ enhancement on α-amylase synthesis has a lag period of 3 to 4 hours and a fast and constant accumulation of this enzyme takes place after 12 hours of hormone treatment (Fig. 1). Potent transcription inhibitors, such as cordycepin (3′-deoxyadenosine), added at the same time as GA₃ administration effectively abolish the hormonal effect on α-amylase synthesis (6). However, this inhibitory effect of cordycepin on α-amylase synthesis is progressively decreased when the time of its addition is delayed and cordycepin does not inhibit α-amylase at all if it is added 12 hours or later after hormone administration (5). Since the effectiveness of cordycepin on RNA synthesis (cordycepin apparently inhibits both transcription and poly(A) addition in barley aleurone cells) does not change appreciably when its addition is delayed, this observation indicates the following.