Regulation of the synthesis of barley aleurone α-amylase by gibberellic acid and calcium ions

Abstract

The effects of gibberellic acid (GA3) and calcium ions on the production of α-amylase and acid phosphatase by isolated aleurone layers of barley (Hordeum vulgare L. cv Himalaya) were studied. Aleurone layers not previously exposed to GA3 or Ca2+ show qualitative and quantitative changes in hydrolase production following incubation in either GA3 or Ca2+ or both. Incubation in H2O or Ca2+results in the production of low levels of α-amylase or acid phosphatase. The addition of GA3 to the incubation medium causes a 10- to 20-fold increase in the amounts of these enzymes released from the tissue, and addition of Ca2+ at 10 millimolar causes a further 8- to 9-fold increase in α-amylase release and a 75% increase in phosphatase release. Production of α-amylase isoenzymes is also modified by the levels of GA3 and Ca2+ in the incubation medium. α-Amylase 2 is produced under all conditions of incubation, while α-amylase 1 appears only when layers are incubated in GA3 or GA3 plus Ca2+. The synthesis of α-amylases 3 and 4 requires the presence of both GA3 and Ca2+ in the incubation medium. Laurell rocket immuno-electrophoresis shows that two distinct groups of α-amylase antigens are present in incubation media of aleurone layers incubated with both GA3 and Ca2+, while only one group of antigens is found in media of layers incubated in GA3 alone. Strontium ions can be substituted for Ca2+ in increasing hydrolase production, although higher concentrations of Sr2+ are required for maximal response. We conclude that GA3 is required for the production of α-amylase 1 and that both GA3 and either Ca2+ or Sr2+ are required for the production of isoenzymes 3 and 4 of barley aleurone α-amylase.