CHARACTERIZATION AND LIPID-COMPOSITION OF THE PLASMA-MEMBRANE IN GRAPE LEAVES

Plasma membranes have been isolated from grape leaves using a two-phas e aqueous polymer technique which differed from the usual procedure in order to counter difficulties posed by the fibrous nature and high st arch content of this material. The lipid composition (sterols, phospho lipids + sphingolipids and their fatty acids) of the purified plasma m embrane was determined and compared with that of the microsomal fracti on (100 000 g). The major differences between the membrane and microso mal fractions were increases in the proportions of stearic acid, phosp hatidylcholine and, to a lesser extent, phosphatidylethanolamine and a decrease in linolenic acid. Phosphatidylglycerol and diphosphatidylgl ycerol were present in the microsomal fraction, but not in the plasma membrane. Unusually large amounts of cerebrosides (compared with some other plant species) were found in both membrane fractions. The lipid composition of the plasma membrane is discussed in the context of memb rane fluidity.