Role of Plasmalemma Microdomains (Rafts) in Protection of the Plant Cell Under Osmotic Stress.

Lipid-protein microdomains (presumably rafts) of the plasmalemma isolated from the beetroots subjected to hyperosmotic stress and hypoosmotic stress were studied. In these microdomains, the variations in the composition of total lipids, sterols, and fatty acids were observed. These variations differed under hypo- and hyperosmotic types of stress. We presumed that such variations were bound up with different strategies, which are probably related to protecting the cell from osmotic stress. One of the protection tendencies might be related, in our opinion, to credible growth of the content of such lipids as sterols and sterol esters, which are considered as raft-forming. Under osmotic stress, these lipids can contribute to the formation of both new raft structures and new membrane contacts of plasmalemma with intracellular organelles. Another protection tendency may be bound up with the redistribution of membrane phospholipids and phosphoglycerolipids possibly to stabilize the membrane's lamellar structure, which is ensured by credible growth of the content of such lipids as phosphatidylcholines, phosphatidylinositols, and digalactosyldiacylglycerol. The participation of lipid-protein microdomains in the adaptive mechanisms of plant cells may, in our opinion, also be bound up with the redistribution of membrane sterols, which (redistribution) in a number of variants may provoke credible growth in the content of cholesterol or "anti-stress" sterols (campesterol and stigmasterol). So, according to our results, the variations in the content of the plasmalemma lipid-protein microdomains take place under osmotic stress. These variations may influence the functioning of plasmalemma and take part in the adaptive mechanisms of plant cells.