Exocytosis in plants

Abstract

Exocytosis is the final event in the secretory pathway and requires the fusion of the secretory vesicle membrane with the plasma membrane. It results in the release to the outside of vesicle cargo from the cell interior and also the delivery of vesicle membrane and proteins to the plasma membrane. An electrophysiological assay that measures changes in membrane capacitance has recently been used to monitor exocytosis in plants. This complements information derived from earlier light and electron microscope studies, and allows both transient and irreversible fusion of single exocytotic vesicles to be followed with high resolution in protoplasts. lt also provides a tool to investigate bulk exocytotic activity in single protoplasts under the infiuence of cytoplasmic modulators. This research highlights the role of intracellular Ca 2 +, GTP and pressure in the control of exocytosis in plants.In parallel to these functional studies, plant proteins with the potential to regulate exocytosis are being identified by molecular analysis. In this review we describe these electrophysiological and molecular advances, and emphasise the need for parallel biochemical work to provide a complete picture of the mechanisms controlling vesicle fusion at the plasma membrane of plant cells.

Physiological anatomy and function of the membranous grass ligule

“…The material is finally packaged into smooth-surfaced vesicles which bleb off the trans aspect of the dictyosome, and are transported to the plasmalemma. The mechanism of vesicle movement and their apparent targeting to particular regions of the cell (the plasmalemma next to the outer tangential wall) are areas of considerable research interest (Thiel & Battey, 1998 ;Battey et al, 1999), but remain unexplored in this system. Ultimately, however, fusion of the vesicles with the plasmelemma gives rise to paramural bodies and permits their contents to be disgorged into the periplasmic space where they accumulate.…”

Tansley Review No. 108

“…Each of these pathways must be under tight metabolic control. While there is still little detail of how such regulation is achieved, it is clear that secretion is subject to hormonal and environmental cues and must generally be regulated in conjunction with changes in cell size during expansive cell growth and development (Battey & Blackbourn, 1993 ;Thiel & Battey, 1998).…”

“…New tools for measuring and manipulating vesicle traffic and secretion are now coming to the fore, drawing on in vivo fluorescence and capacitance recording as well as genetic engineering (Gillis, 1995 ;Homann & Tester, 1998 ;Miesenbock et al, 1998). These new technologies have already begun to yield details wholly unexpected from past studies (Thiel & Battey, 1998). Various aspects of protein sorting and secretion in plant cells have been discussed broadly in a number of excellent reviews (Battey & Blackbourn, 1993 ;Beevers & Raikhel, 1998 ;Neuhaus & Rogers, 1998 ;Robinson et al, 1998 ;Thiel & Battey, 1998 ;Battey et al, 1999 ;Sanderfoot & Raikhel, 1999).…”

“…These new technologies have already begun to yield details wholly unexpected from past studies (Thiel & Battey, 1998). Various aspects of protein sorting and secretion in plant cells have been discussed broadly in a number of excellent reviews (Battey & Blackbourn, 1993 ;Beevers & Raikhel, 1998 ;Neuhaus & Rogers, 1998 ;Robinson et al, 1998 ;Thiel & Battey, 1998 ;Battey et al, 1999 ;Sanderfoot & Raikhel, 1999). Here we focus on recent findings relating to the mechanisms of vesicle trafficking and the background to these developments, highlighting both current understanding of the molecular events of secretion and the gaps therein, as well as discussing emerging themes from work with plants.…”

“…In root cap cells and gland cells secretion is localized primarily to the outer tangential surface of the cell (Chaboud & Rougier, 1981). Measurement of vesicle fusion in single plant cells has only just begun using patch-clamp recording (Thiel & Battey, 1998). While these techniques offer unrivalled temporal resolution of fusion events in vivo, their application to plant cells also raises some questions that may best be answered through studies of stimulus-evoked secretion (Battey & Blackbourn, 1993 ;Staehelin & Moore, 1995 ;Robinson et al, 1998 ;Thiel & Battey, 1998 ;Battey, et al, 1999).…”