Sorting of membrane proteins to vacuoles in plant cells

Plant cells may generate and maintain at least two separate vacuolar organelles, storage vacuoles and lytic vacuoles. In contrast to the relatively well-studied vacuolar sorting mechanisms for some soluble proteins in plant cells, little is known about the mechanisms of membrane protein sorting to these separate organelles, a process which is facilitated by transport vesicles and requires targeting information within the integral membrane proteins. During the past few years, the identification of a sorting receptor, an integral membrane protein for the lytic vacuole pathway, and the purification and characterization of novel dense vesicles that traffic to protein storage vacuoles in plant cells have provided new markers for studying the traffic of membrane proteins to vacuoles. Here we discuss recent progress in biochemical studies of vacuolar targeting of integral membrane proteins and immunocytochemical characterization of these newly identified transport vesicles. Possible models of sorting mechanisms in plant cells will be presented. (C) 1999 Published by Elsevier Science Ireland Ltd. All rights reserved.