A comparison of the effects of Ca2+ and gibberellic acid on enzyme synthesis and secretion in barley aleurone

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Abstract
The effects of the addition and withdrawal of gibberellic acid (GA3) and Ca2+ on enzyme synthesis and secretion by barley (Hordeum vulgare L. cv. Himalaya) aleurone layers were studied. Incubation of layers in GA3 plus Ca2+ affects the total amount of secreted α‐amylase (EC 3.2.1.1) and acid phosphatase (EC 3.1.3.2) by promoting the appearance of different isoenzymic forms of these enzymes. The release of α‐amylase isoenzymes 1–4 in response to GA3 plus Ca2+ has a lag of 6 h. When layers are incubated in GA3 alone for 6 h prior to the addition of Ca2+, isoenzymes 1–4 appear in the medium after only 30 min. When the addition of Ca2+ to layers pretreated in GA3 is delayed beyond 12 h, its effectiveness in stimulating the synthesis and release of isoenzymes 3 and 4 is diminished. After 35 h of preincubation in GA3, addition of Ca2+ will not stimulate synthesis of α‐amylase isoenzymes 3 and 4. Aleurone layers preincubated for 6 h in GA3 will respond to Ca2+ when the GA3 is withdrawn from the incubation medium by producing α‐amylase isoenzymes 1–4. The converse is not the case, however, since layers preincubated in Ca2+ for 6 h will not produce all isoenzymes of α‐amylase when subsequently incubated in GA3. The Ca2+‐stimulated release of α‐amylase from GA3 pre‐treated layers is dependent on the time of incubation in Ca2+ and the concentration of the ion. The response to Ca2+ is temperature‐dependent, and other divalent cations such as Mg2+ cannot substitute for Ca2+. We conclude that Ca2+ influences α‐amylase release by influencing events at the biochemical level.