Phosphatidic acids, isolation cells

There is a scarcity of data for the analyses of glyoxysomal membranes and plasma membranes of plant cells. The glyoxysomal membrane from castor bean (Ricinus communis L.) endosperm has PC as the major lipid together with PE, 80% of the phospholipid can be accounted for. Plasma membranes isolated from oat Avena saliva L.) roots showed relatively lai ge amounts of phosphatidic acid (PA), (1,2-diacyl-jn-glycerol 3-phosphate) and an unknown lipid (Keenan et al., 1973). It is possible that some lipid degradation took place in the preparation of this sample. Further analyses of the lipid composition would be most appropriate. The analyses of Keenan et al. (1973) indicated that only 28.6% of the plasma membrane lipid was phospho-... 

In higher plants, the lipolytic enzymes and their physiological functions are not well characterized [1]. iMost reports demonstrated that phospholipid catabolism in plants is achieved by the concerted actions of membrane-bound enzymes including phospholipase D, phosphatidate phosphatase, lipolytic acyl hydrolases and lipoxygenases [1,2]. With the exception of the phospholipase D, the literature on plant phospholipases is still very limited. We previously reported that tonoplast from Acer pseudoplatanus cells contains small amounts of phosphatidic acid and lysophospholipids, which were produced together with free fatty acids, particularly after addition of Ca " [31. These data suggested the possible involvement of phospholipase D and phospholipase A in the metabolism of vacuolar membrane lipids. The phospholipase activities were studied by following the hydrolysis of added sn-2-[14c]linoleyl-PC to tonoplast vesicles. Tonoplast was obtained by osmotic lysis of pure preparations of vacuoles isolated from protoplasts derived from Acer pseudoplatanus cells [4]. This present work demonstrated clearly the presence of phospholipase D and phospholipase Ai activities associated with the tonoplast of Acer, The phospholipase Ai showed an optimal activity at pH about 6-6.5, did not necessarily require divalent cations, but was stimulated by Mg- and particularly by Ca. This work presents the first evidence for the presence of phospholipases A in plant cells. 

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