Proton Pump and ATPase Activities in Tonoplast Vesicles from Storage Tissue of Red Beet

Abstract

Preparations of sealed membrane vesicles represent an ideal experimental system for studying mechanisms of membrane transport (Turner, 1983 for review). With the development of the methodology to isolate sealed membrane vesicles from plant cells by Sze (1980), this valuable tool could then be applied to the study of transport across plant membranes. Using this system, a number of laboratories have recently characterized ATP-dependent H+ transport in membrane vesicles isolated from homogenates of plant tissue (Hager et al. 1980; Rasi-Caldogno et al. 1981; Dupont et al. 1982; Mettler et al. 1982; Bennett and Spanswick 1983; Churchill et al. 1983). From these studies, it appears that two distinct types of H+-transporting ATPase can be observed in plant vesicle preparations (Churchill et al. 1983 and references therein). One type of ATPase is stimulated by anions, inhibited by N03 - and insensitive to vanadate while the other type of ATPase is stimulated by cations and inhibited by vanadate (Churchill et al. 1983 and references therein). Both types of H+-transporting ATPase are insensitive to oligomycin and NaN3 (Sze, 1983; Dupont et al. 1982; Churchill and Sze, 1983) which indicates that they are not representative of mitochondrial ATPase. These two types of H+-transporting ATPase can be separated on sucrose or dextran density gradients (Churchill et al. 1983) which suggests that they are associated with different membrane components of the plant cell.