Lipids of Ectocarpus fasciculatus (Phaeophyceae). Incorporation of [l-14C]Oleate and the Role of TAG and MGDG in Lipid Metabolism

Abstract

Lipids and fatty acids of Ectocarpus fasciculatus (Ectocarpales, Phaeophyceae) were analyzed. Major polar lipids are monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG), diacylglycerylhydroxymethyl-iV.A'j.N-trimethyl/J-alanine (DGTA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and phosphatidylinositol (PI). Diphosphatidylglycerol (OPG), phosphatidic acid (PA) and phosphatidyl-O-[iV-(2-hydroxyethyl)glycine] (PHEG) were also present in small amounts. Nonpolar lipids mainly consist of triacylglycerol (TAG) and diacylglycerol (DAG). Major fatty acids are 16:0,18:1, al8:3, 18:4, 20:4 and 20:5. The positional distribution of fatty acids showed that molecular species of eukaryotic structure account for 99% in MGDG, 98% in DGDG, 62% in PG and 23% in SQDG. On incubation with [1- 14 C]18:1 for 30 min, 33% of the total label was detected in TAG, 16% in PG, 14% in PE, 10% in PC and 8% in MGDG. During 7 days of chase, the label in TAG, PG, PE and PC decreased and simultaneously increased in MGDG up to 41% of the total. In SQDG, labelled fatty acids were found in prokaryotic as well as in eukaryotic molecular species. During the experiment, the label shifted from 18:1 to 18:2, 18:3,18:4 and, to a minor extent, to 20:4 and 20:5 acids indicating 18:1 to be processed by elongation and/or desaturation. These results suggest TAG to act as a major primary acceptor of exogenous oleate and to be involved in the transfer of fatty acids to MGDG and other polar lipids.