Lipids of Pavlova lutheri: Cellular site and metabolic role of DGCC

Pavlova lutheri contains triacylglycerols (TAG), monogalactosyldiacylglycerols (MGDG), galactosyldiacylglycerols (DGDG), sulfoquivonosyldiacylglycerols (SQDG), diacylglyceryl hydroxymethyl-N,N,N-trimethyl-beta-alanine (DGTA), diacylglyceryl carboxyhydroxymethylcholine (DGCC) and diacylglyceryl glucuronide (DGGA) as major lipid components. Prominent fatty acids are 14:0, 16:0, 16:1, 18:4, 20:5, 22:5 and 22:6. In MGDG and DGDG, 18:4 and 20:5 predominate, while SQDG contains high proportions of 14:0 and 16:0. DGCC is enriched in 16:0 and 20:5, DGGA in 18:1, 22:5 and 22:6, and DGTA in 22:6. Analysis of subcellular membrane fractions demonstrated an accumulation of DGCC, DGTA and DGGA in non-plastid membranes. On incubation of cells with [1-C-14] oleic acid, after 60 min of pulse, 30% of the incorporated label was found in TAG and 70% in polar lipids. DGCC (52%) and DGTA (12%) were the most strongly labelled polar lipids. Within 72 h of chase, in DGCC and in TAG the label rapidly decreased to 11% and 17%, respectively, but in MGDG it increased in the same time up to 35% of the total. Only minor changes were observed in DGTA and no significant label was recorded in DAG during the chase-period. The shift of label from 18:1 to 18:4, 20:5 and 22:6 reflected further elongation and/or desaturation of the substrate. Very similar results obtained using [2-C-14] acetate as precursor suggested that DGCC acts as a primary acceptor of de novo-formed or exogenous fatty acids which subsequently undergo processing and redistribution. It Is suggested that C-18 and C-20 fatty acids are transferred individually from the cytoplasm to the chloroplast allowing the synthesis of eukaryotic MGDG without the import of DAG. (C) 1997 Elsevier Science Ltd. All rights reserved.