Calcium Uptake and Exchange in Barley Aleurone Layers and Protoplasts During Ca-Stimulated Amylase Secretion
Extracellular Ca2+ regulates α-amylase secretion in isolated barley aleurone layers. At high Ca2+ concentrations (1–10 mM) the secretion of isozymes of α-amylase with high isoelectric points (high pI) is greatly stimulated. This effect is rapidly reversed by withdrawing Ca2+ and is specific for Ca2+. Extracellular Ca2+ may exert its effect either directly on the plasma membrane or by altering the Ca concentration of some compartment inside the cell. We have determined the influence of extracellular Ca2+ on intracellular Ca pools by measuring Ca uptake and exchange in aleurone layers and by direct measurement of cytoplasmic Ca2+ activity in aleurone protoplasts.