Calcium Uptake and Exchange in Barley Aleurone Layers and Protoplasts During Ca-Stimulated Amylase Secretion

Abstract

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.