The Control of α-Amylase Synthesis by Calcium in the Barley Aleurone
Barley aleurone layers synthesize and secrete at least four isozymes of α-amylase which are separated by various criteria (including isoelectric points) into two groups: A (low pI; isozymes 1 and 2) and B (high pI; isozymes 3 and 4). Isozyme 2 is produced under all conditions of aleurone incubation but its rate of accumulation is enhanced by the presence of gibberellic acid (GA). Isozyme 1 requires GA for its production as do isozymes 3 and 4. Isozymes 3 and 4 also require Ca2+ for their accumulation in and secretion from aleurone layers; the production and secretion of isozymes 1 and 2 is completely independent of the level of Ca2+ in the external medium. The dependence of amylase secretion on Ca2+ has been investigated previously and shown to be specific to the B group (Jones, R. L. and Jacobsen, J. V., 1982, Planta 156:421–432), and the Ca2+ requirement was demonstrated to be at the level of the plasma membrane (Moll, B. A. and Jones, R. L., 1982, Plant Physiology 70:1149–1155). The work presented here concerns the effect of Ca2+on amylase synthesis.