ATP-dependent formation of phosphatidylserine-rich vesicles from the endoplasmic reticulum of leek cells

Leek (Allium porrum) plasma membrane is enriched in phosphatidylserine (PS) by the vesicular pathway, in a way similar to that already observed in ani mal cells (B. Sturbois-Balcerzak, D.J. Morre, O. Loreau, J.P. Noel, P. More au, C. Cassagne [1995] Plant Physiol Biochem 33: 625-637). In this paper we document the formation of PS-rich small vesicles from reek endoplasmic ret iculum (ER) membranes upon addition of ATP and other factors. The omission of ATP or its replacement by ATP gamma-S prevents vesicle formation. These vesicles correspond to small structures (70-80 nm) and their phospholipid c omposition, characterized by a PS enrichment, is compatible with a role in PS transport. Moreover, the PS enrichment over phosphatidylinositol in the ER-derived vesicles is the first example, to our knowledge, of phospholipid sorting from the ER to ER-derived vesicles in plant cells.