Lipid Composition of Plasma Membranes and Tonoplasts Isolated from Etiolated Seedlings of Mung Bean (Vigna radiata L.)

Abstract

The lipid composition of plasma membranes and tonoplasts from etiolated mung bean hypocotyls was examined in detail. Phospholipids, sterols, and ceramide monohexoside(s) were the major lipid classes in both membranes. The content of phospholipids on a protein basis was higher in the tonoplast, but the content of total sterols was similar in both membranes. Accordingly, the sterol to phospholipid molar ratio in the plasma membrane was higher than that of the tonoplast. Phosphatidylethanolamine and phosphatidylcholine comprised the major phospholipids in both membranes. Phosphatidylinositol, phosphatidylserine, and phosphatidylglycerol were identified as minor phospholipid components. The content of phosphatidylinositol and phosphatidylglycerol was relatively high in the tonoplast, comprising 11 and 5% of the total phospholipids, respectively. Although special care was taken against the degradative action of phospholipase D and phosphatidic acid phosphatase during the isolation of these membranes, by adding EDTA, EGTA, KF, choline, and ethanolamine to the homogenizing medium, significant amounts of phosphatidic acid, about 15% of the total phospholipids, were detected in the plasma membrane. On the other hand, the content of phosphatidic acid in tonoplasts and other membrane fractions was very low. This fact may indicate that high levels of phosphatidic acid occur naturally in plasma membranes. Phosphatidylglycerol in both membranes and phosphatidylinositol in the tonoplast contained high levels of palmitic acid, which comprised more than 50% of the total fatty acids. Significant differences were observed in the sterol compositions of plasma membranes and tonoplasts. More than 90% of the sterols in the plasma membrane were unesterified, while the tonoplast was enriched in glycosylated sterols, especially acylated sterylglycosides. Ceramide monohexoside was found to be specifically located in these membranes, in particular, in the tonoplast, in which it comprised nearly 17% of the total lipids. is quite limited regarding the lipid composition of plasma membranes and tonoplasts, which also possess very important physiological functions including in the former, transport (22), cell wall biosynthesis (14), hormone action (24), phytochrome responses (18), and disease resistance (27), and in the latter, cellular compartmentation of lytic enzymes, acids, ions, and secondary products (I 1, 13). In addition, these membranes have been shown to play an important role in cold acclimation (29,31,33), freezing injury (26), and chilling stress (32).Recently we have established isolation methods for plasma membranes and tonoplasts from etiolated mung bean hypocotyls (34,35). In the present study, we have analyzed the lipid composition of both membranes and compared them. Plasma membranes are characterized by their high content of phosphatidic acid and tonoplasts by their high content of ceramide monohexoside. MATERIALS AND METHODSPlant Materials. Seeds of mung bean (Vigna radiata [L] Wilczek) were imbibed and germinate...

Comparison of the Lipid Composition of Oat Root and Coleoptile Plasma Membranes

“…In both the coleoptile and the root, PC and PE appeared in almost equal molar amounts and, aside from PA, were the most abundant phospholipids, while the other phospholipids (LPC, PI, PS, PG) were present in significantly reduced amounts. These results are typical of plant PM analyses (19,21,22,(33)(34)(35). Of interest here was the elevated amount of lysolecithin (LPC) in the oat root (1.7 mol %) when compared to the coleoptile (approximately 0.6 mol %).…”

Analysis of Glucocerebrosides of Rye (Secale cereale L. cv Puma) Leaf and Plasma Membrane

“…Recently, however, glucocerebrosides have been identified as a major lipid component of the plasma membrane and tonoplast of cells of several plant species. Plasma membrane isolated from rye (18) and barley (27) leaves, oat root (28), oat coleoptile (28), and mung bean hypocotyl (33) …”

“…Recently, however, glucocerebrosides have been identified as a major lipid component of the plasma membrane and tonoplast of cells of several plant species. Plasma membrane isolated from rye (18) and barley (27) leaves, oat root (28), oat coleoptile (28), and mung bean hypocotyl (33) 'Supported in part by the U.S. Department of Agriculture Com have been reported to contain glucocerebrosides at levels of 16,23,10,26, and 7 mol%, respectively, of the total plasma membrane lipid. In addition, the tonoplast of mung bean hypocotyl cells reportedly contains 17 mol% glucocerebroside (33).…”

Mycotoxins reveal connections between plants and animals in apoptosis and ceramide signaling

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