| The 14CO2- and [1-14C]-acetate-labelling of fatty acids (FA) of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and monogalactosyldiacylglycerol (MGDG) of Vicia faba leaves indicated that 14C-label was not evenly distributed among the FA of these lipids. Instead, labelled saturated and monounsaturated FA were combined with unlabelled polyunsaturated FA. Double labelling [1- 14C]-acetate and [1,2,3-3H]-glycerol experiments showed that the H-labelled glycerol was not necessarily associated with newly formed 14C-FA in PC and MGDG. Immediately after feeding 3H-glycerol was attached predominantly to unlabelled, polyunsaturated FA. This suggests that newly synthesized FA are exchanged with polyunsaturated FA on PC and that the DAG precursors of PC and MGDG are both highly unsaturated. Through random deacylation/reacylation between the FA of PC and an acyl-CoA pool, the DAG subsequently formed is maintained in a highly unsaturated state. Cytosolic and chloroplastic lipids could then be synthesized directly from this DAG pool that contain unsaturated FA similar to those in PC. |
