MONENSIN BLOCKS THE TRANSFER OF VERY LONG-CHAIN FATTY-ACID CONTAINING LIPIDS TO THE PLASMA-MEMBRANE OF LEEK SEEDLINGS - EVIDENCE FOR LIPID SORTING BASED ON FATTY ACYL CHAIN-LENGTH

Delivery of newly synthesized fatty acids and lipids to the plasma membrane in leek seedlings via the endoplasmic reticulum (ER)-Golgi apparatus pathway is primarily by bulk transport (without sorting). However, pulse-chase experiments revealed kinetics of transport of lipids with VLCFA (very long chain fatty acids having more than 18 carbon atoms) in favor of a preferential transfer of these molecules to the plasma membrane. Use of monensin showed the accumulation of lipids in the Golgi apparatus and a related decrease of the amount of lipids transported to the plasma membrane. Lipid and fatty acid analyses revealed that transport of VLCFA-containing phospholipids was most strongly inhibited by the monensin block. These results taken together with an inability of the plasma membrane to synthesize VLCFA support a role for the Golgi apparatus in VLCFA delivery to the plasma membrane and leads to the hypothesis of a sorting function as well, based on fatty acyl chain length.