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

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.