How sterols affect protoplasts plasma membrane water permeability and their volume under osmotic shock.

Protoplasts isolated from Arabidopsis leaves were used to study the initial stages of the plant cell response to osmotic stress. The role of sterols in these processes was investigated by their extraction from the protoplast plasma membrane in the presence of the oligosaccharide - methyl-β-cyclodextrin (MβCD). Depletion of membrane sterols caused by MβCD treatment did not alter protoplast volume under isosmotic conditions; however, volumes changed significantly when protoplasts were exposed to osmotic stress.

Sterol Extraction from Isolated Plant Plasma Membrane Vesicles Affects H-ATPase Activity and H-Transport.

Plasma membrane H-ATPase is known to be detected in detergent-resistant sterol-enriched fractions, also called "raft" domains. Studies on H-ATPase reconstituted in artificial or native membrane vesicles have shown both sterol-mediated stimulations and inhibitions of its activity. Here, using sealed isolated plasma membrane vesicles, we investigated the effects of sterol depletion in the presence of methyl-β-cyclodextrin (MβCD) on H-ATPase activity.

Involvement of plasma membrane H-ATPase in diamide-induced extracellular alkalization by roots from pea seedlings.

The plasma membrane H-ATPase can be considered as a redox-dependent enzyme, because diamide-mediated inhibition of its hydrolytic and transport activities is accompanied by alkalization of the rhizosphere and retardation of root growth. Plasma membranes were isolated from roots of etiolated pea seedlings treated in the presence of an oxidant-diamide and an inhibitor of redox-sensitive protein phosphatase-phenylarsine oxide. Hydrolytic and proton transport activities of H-ATPase were determined.