Control of α-Amylase mRNA Accumulation by Gibberellic Acid and Calcium in Barley Aleurone Layers

Abstract

Pulse-labeling of barley (H. vulgare L. cv. Himalaya) aleurone layers incubated for 13 h in 2.5 .mu.M GA3 with or without 5 mM CaCl2 shows that .alpha.-amylase isozymes 3 and 4 are not synthesized in vivo in the absence of Ca2+. A c[complementary]DNA clone for .alpha.-amylase was isolated and used to measure .alpha.-amylase mRNA levels in aleurone layers incubated in the presence and absence of Ca2+. No difference was observed in .alpha.-amylase mRNA levels between layers incubated for 12 h in 2.5 .mu.M GA3 with 5 .mu.M CaCl2 and layers incubated in GA3 alone. RNA isolated from layers incubated for 12 hours in GA3 with and without Ca2+ was translated in vitro and was found to produce the same complement of translation products regardless of the presence of Ca2+ in the incubation medium. Immunoprecipitation of translation products showed that the RNA for .alpha.-amylase synthesized in Ca2+-deprived aleurone layers was translatable. Ca2+ is required for the synthesis of .alpha.-amylase isozymes 3 and 4 at a step after mRNA accumulation and processing.