Regulation of the Synthesis of Barley Aleurone α-Amylase by Gibberellic Acid and Calcium Ions

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Abstract
The effects of GA3 and Ca2+ on the production of .alpha.-amylase and acid phosphatase by isolated aleurone layers of barley (H. 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 .alpha.-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 mM 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 GA3 and Ca2+ 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 GA3 or GA3 plus Ca2+. The synthesis of .alpha.-amylases 3 and 4 requires the presence of both GA3 and Ca2+ in the incubation medium. Laurell rocket immunoelectrophoresis shows that 2 distinct groups of .alpha.-amylase antigens are present in incubation media of aleurone layers incubated with both GA3 and Ca2+, while only 1 group of antigens is found in media of layers incubated in GA3 alone. Sr2+ can be substituted for Ca2+ in increasing hydrolase production, although higher concentrations of Sr2+ are required for maximal response. GA3 is required for the production of .alpha.-amylase 1, and both GA3 and either Ca2+ or Sr2+ are required for the production of isoenzymes 3 and 4 of barley aleurone .alpha.-amylase.