ABSTRACT
Biological membranes of living cells consist of a bilayer of polar lipids, predominantly glycerolipids, into which hydrophobic proteins are embedded. Phosphatidic acid, which was first isolated from cabbage leaf by Chibnall and Channon represents a central intermediate in phospholipid metabolism. Phosphatidylglycerol is the only phospholipid in thylakoid membranes, but is also present in extraplastidic membranes including endoplasmic reticulum, plasma membrane and mitochondria. The glycerol backbone of glycerolipids originates from dihydroxyacetone-phosphate, which in turn is derived from glycolysis. Glycerolipids in plants are synthesised from phosphatidic acid following two different pathways: the ‘diacylglycerol pathway’ or the ‘cytidine diphosphate-diacylglycerol pathway’. Glycerolipids of plants are subject to constant turnover by lipid hydrolysing enzymes, phospholipases and galactolipases. Phospholipase C hydrolyses the ester bond between the glycerol and the phosphate group of phospholipids, thus releasing diacylglycerol and the respective phosphorylated head group. Fatty acids are hydrolysed from membrane lipids by action of phospholipases or glycolipases.
