MODULATION OF CALMODULIN MESSENGER-RNA AND PROTEIN-LEVELS IN BARLEY ALEURONE

Changes in calmodulin (CaM) mRNA and protein were investigated in aleu rone layers of barley (Hordeum vulgare L. cv Himalaya) incubated in th e presence and absence of calcium, gibberellic acid (GA(3)), and absci sic acid (ABA). CaM mRNA levels increased rapidly and transiently foll owing incubation of aleurone layers in H2O, CaCl2, or GA(3). The incre ase in CaM mRNA was prevented by ABA. This increase in CaM mRNA was br ought about by physical stimulation during removal of the starchy endo sperm from the aleurone layer. CaM protein levels did not increase in response to physical stimulation. Only incubation in GA(3) plus CaCl2 brought about a rapid increase in CaM protein levels in the aleurone c ell. ABA reduced the level of CaM protein below that found at the begi nning of the incubation period. The rise in CaM protein preceded incre ases in the synthesis and secretion of alpha-amylase. Immunocytochemis try with monoclonal antibodies to carrot and mung bean CaM was used to localize CaM in aleurone protoplasts. Monoclonal antibodies to tubuli n and polyclonal antibodies to tonoplast intrinsic protein and malate synthase were used as controls. CaM was localized to the nucleus, the vacuolar membrane, and the cytosol, but was not associated with microt ubules.