Regulation of the synthesis of barley aleurone alpha-amylase by gibberellic Acid and calcium ions.

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