Some properties of Proton Pumping ATPases at the Plasma Membrane and Tonoplast of Guard Cells

Abstract

The kinetics and magnitude of light-stimulated H + -efflux at the plasma membrane of guard cells can be directly correlated with stomatal opening in epidermal strips, under conditions where K + fluxes and osmotic changes have already been well characterised ( e.g. MacRobbie 1988). Our data is consistent with the action of a plasma membrane ATPase in generating the H + -efflux. Purification of GCP has allowed more detailed investigation of the spectral requirements for light-stimulated H + -efflux and has facilitated electrophysiological studies using patch clamp techniques. GCP also provide a homogeneous cell type as the starting point for biochemical studies on guard cells. The ATP-hydrolysing activities of both the plasma membrane ATPase and tonoplast ATPase, and the H + -transport properties of the tonoplast ATPase can be distinguished in crude homogenates of GCP. Application of electrophoretic separation in conjunction with labelling techniques may allow resolution of the individual polypeptides of these ATPases.