Divalent cation inhibition of barley root plasma membrane‐bound Ca²⁺‐ATPase activity and its reversal by monovalent cations

Abstract

The inhibitory action of divalent cations on the Ca 2+ ‐ATPase activity of a plasma membrane‐rich microsome fraction isolated from the roots of barley ( Hordeum vulgare L. cv. Conquest) was investigated. Using electron paramagnetic resonance spectroscopy to measure cation‐induced changes in membrane lipid properties, it was demonstrated that certain divalent cations (Ca 2+ , Cd 2+ , UO 2+ 2 ) inhibit the Ca 2+ ATP‐ase by restriction of lipid polar head group mobility and not by alteration of membrane surface potential. Monovalent cations which stimulate the Ca 2+ ‐ATPase of barley roots (Na + , K + , ethanolamine HCl) can also reverse the Ca 2+ ‐ATPase inhibition by Cd 2+ . The degree of Na + reversal of Cd 2+ ‐induced Ca 2+ ‐ATPase inhibition was influenced by the nature of the anion.