Phosphatidylglycerol Synthesis in Spinach Chloroplasts: Characterization of the Newly Synthesized Molecule

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Abstract
Intact chloroplasts from spinach (S. oleracea L., hybrid 424) readily incorporate [14C]glycerol-3-phosphate and [14C]acetate into diacylglycerol, monoacylglycerol, diacylglycerol, free fatty acids (only when acetate is the precursor), phosphatidic acid, phosphatidylcholine and most notably phosphatidylglycerol. The fraction of phosphatidylglycerol synthesized is greatly increased by the presence of MnCl in the reaction mixture. Glycerol-3-phosphate-labeled phosphatidylglycerol is equally labeled in the 2 glycerol moieties of the molecule. Acetate-labeled phosphatidylglycerol is equally labeled in both acyl groups. Position 1 contains primarily oleate, linoleate and small amounts of palmitate. Position 2 contains primarily palmitate. No radioactive trans-.DELTA.3-hexadecenoate was detected. The labeling patterns indicative that the radioactive phosphatidylglycerol is the product of de novo chloroplast lipid biosynthesis and phosphatidylglycerol may be a substrate for fatty acid desaturation.