Plant cell organelles microsomes

Several observations concerning the lipids of plant cell organelles have suggested that lipid exchange can occur between the different membranes of plant cells. (1) Numerous analyses of cell membranes have been realized since refined chromatographic techniques were first developed, and all results have pointed out a real uniformity in the phospholipid and fatty acid contents of all cell membranes, within the same species, except for chloro-plast membranes (Mazliak et al., 1975 Mazliak, 1977). (2) Membrane lipids were proved to turn over continuously in cell organelles with half-lives varying from 3 days in microsomes to 10 days in mitochondria (Mazliak et al., 1968 Ben Abdelkader and Mazliak, 1971). However, carefully purified mito-... 

To determine which organelles were involved in lipid synthesis, plant cell organelles (mitochondria, microsomes, peroxisomes, plasmalemma, nuclei) were isolated in vitro and fed with various radioactive precursors ([ C]ace-tate or [ C]acetyl-CoA, [ K ]malonate or [ K ]malonyl-CoA, [ P]phos-phate, [ C]glycerol or [ K]l]glycerophosphate, [ C]choline or [ CJethanola-mine, etc.). The biosynthetic capacities of each organelle were thus evidenced (see Mazliak, 1975, 1977) in an effort to locate the sites of lipid synthesis in plant cells. The following points appeared clearly from the experiments ... 

On the contrary, the microsomes of plant cells proved to contain all the enzymes necessary for the biosynthesis of either polyunsaturated fatty acids (at least linoleic acid (Vijay and Stumpf, 1971 Ben Abdelkader et al., 1973 Kader, 1977a) or the m or phospholipids of plant membranes i.e., phosphatidylcholine and phosphatidylethariolamine (Devor and Mudd, 1971 Moore et al., 1973). Therefore one was forced to the conclusion that there must be a transfer of lipids from microsomes to other intracellular organelles to correlate the limited synthetic capabilities of the various organelles with the uniformity of their lipid composition. We proposed, in 1968 (Mazliak et al., 1968), that an intermembrane phospholipid exchange was implied in this necessary cooperation between microsomes and other cellular organelles. 

Fig. 4. Localization of WAP27 and WAP20 in the crude microsome fractions and the relation with marker-enzyme activities in three organelles (ER, tonoplast, and Golgi). SDS-PAGE of fractionated proteins by isopycnic linear sucrose density gradient centrifugation of microsome fraction of mulberry cortical parenchyma cells was performed using 6-pL samples in each fraction. Immunoblot analysis was performed with anti-WAP27 and anti-WAP20 antibodies. (From ref. [1], with permission from the American Society of Plant Physiologists.)...

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