Manipulating the Incorporation of [1-14C]Acetate into Different Leaf Glycerolipids in Several Plant Species

Abstract

During short term labeling of expanding leaves of 7 plant species [Spinacia oleracea, Helianthus annuus, Lycopersicon esculentum, Vicia faba, Zea mays, Cucurbita pepo and Petroselinum hortense] with [1-14C]acetate, 35-64% of the label incorporated into lipids was present in phosphatidylcholine and 5-24% in phosphatidylglycerol. In pumpkin, sunflower, broad bean and maize, only 4-12% of the label was present in diacylgalactosylglycerol, but in tomato, parsley and spinach, the proportion was 17-31%. The latter group was distinguished by having diacylgalactosylglycerol containing C16:3. The proportions of total incorporated [1-14C]acetate enterintg the lipids could be manipulated in a predictable manner. Phosphatidylcholine labeling was depressed by treating intact leaves with glycerol or ethylene glycol monomethyl ether or by incubating leaf discs in vitro. An associated increase in phosphatidylglycerol labeling occurred within the 1st group of plants, whereas an increase in labeling of either diacylgalactosylglycerol, phosphatidylglycerol or sulfolipid occurred within the 2nd group. Treating intact leaves with glycerol or incubating leaf discs in vitro elevated cellular concentrations of sn-glycerol 3-phosphate. The 2-pathway hypothesis for glycerolipid biosynthesis, in which phosphatidylcholine is synthesized via a different pathway (eukaryotic) was compared to that for synthesis of phosphatidylglycerol (prokaryotic). Both pathways may contribute toward the synthesis of diacylgalactosylglycerol, with the contribution of each being assessed from the proportion of hexadecatrienoic acid found in the particular plant.