Phospholipid composition of a plasma membrane-enriched fraction from developing soybean roots

Phospholipid polar head group and fatty acid composition were determined for plasma membrane enriched fractions from developing soybean root (Glycine max [L.] Merr. cult. Wells II). Plasma membrane vesicles were isolated from meristematic and mature sections of four-day-old dark grown soybean roots at pH 7.8 and in the presence of 5 millimolar ethylenediaminetetraacetate, 5 millimolar ethyleneglycol-bis (β-aminoethyl ether)N,N tetraacetic acid, and 10 millimolar NaF. Lipid extracts analyzed for phospholipid composition revealed two major phospholipid components: phosphatidylcholine and phosphatidylethanolmine. Minor phospholipid components identified were phosphatidylinositol, phosphatidylserine, phosphatidylglycerol, and diphosphatidylglycerol. Lipid degradation by endogenous phospholipase D during membrane isolation at pH 6.5 and in the absence of chelating agents and NaF resulted in the recovery of large amounts of phosphatidic acid. Phosphatidylcholine was the principal substrate for phospholipase D.