XVI International Botanical Congess

An overview of lipid flow in leek seedlings is presented. After their de novo biosynthesis in the ER and the Golgi apparatus, very long chain fatty acids (VLCFA, more than 18 carbon atoms) are incorporated into phospholipids (PC, PE and PS) and transported to the plasma membrane. We have also found that sterols are transported through the vesicular pathway with similar kinetics as phospholipids. The vesicular nature of the transport process has been demonstrated and the sorting of the VLCFA-containing phospholipids to the vesicular pathway has been determined. Vesicular structures involved in the ER-Golgi apparatus step have been recently isolated and characterized in vitro. The ER-plastid relationship in the synthesis of plastid lipids was also examined in this model. It was proposed that lyso-PC is imported from ?ER to chloroplasts, and further used as substrate for the plastid lipid biosynthesis. In good agreement, i) a lyso-PC acyltransferase activity was shown to be present in the plastid envelope, ii) when incubated in vitro with ER membranes containing labeled lyso-PC, chloroplasts synthesized labeled PC, iii) in vivo, the glycerol moiety of extraplastidial PC was imported at the same rate as the sn-1-bound fatty acids in plastids, and further associated to plastid lipids, but no import of sn-2 fatty acid occurred.