Phase behaviour and molecular species composition of oat root plasma membrane lipids. Influence of induced...

Tolerance to dehydration induced by repeated water-deficit stress is well correlated to changes in the lipid composition of oat root cell plasma membranes. The molecular species of the two dominant phospholipids phosphatidylcholine and phosphatidylethanolamine were determined. The four major species were 16:0/18:2, 16:0/18:3, 18:2/18:2 and 18:2/18:3. In contrast to the large changes in plasma membrane lipid composition in other respects, induced tolerance resulted in very weak alterations concerning the phospholipid molecular species pattern. Only minor alterations, appearing as a decrease in the 18:3-containing lipids, occurred. Total lipids of microsomes and isolated plasma membranes of root cells were analysed by X-ray crystallography at different degrees of hydration. The lipid phase behaviour at different degrees of hydration was further confirmed by polarization microscopy. In the presence of excess water all membrane lipids adopted a reversed micellar configuration. The plasma membrane lipids from root cells with induced dehydration tolerance formed upon dehydration two coexisting lamellar structures. The importance of the phase behaviour at different degrees of hydration for the membrane properties and the relation to membrane composition is discussed.