Sodium transport in plant cells

Salinity limits plant growth and impairs agricultural productivity. There i s a wide spectrum of plant responses to salinity that are defined by a rang e of adaptations at the cellular and the whole-plant levels, however, the m echanisms of sodium transport appear to be fundamentally similar. At the ce llular level, sodium ions gain entry via several plasma membrane channels. As cytoplasmic sodium is toxic above threshold levels, it is extruded by pl asma membrane Na+/H+ antiports that are energized by the proton gradient ge nerated by the plasma membrane ATPase. Cytoplasmic Na+ may also be compartm entalized by vacuolar Na+/H+ antiports. These transporters are energized by the proton gradient generated by the vacuolar H+-ATPase and H+-PPiase. Her e, the mechanisms of sodium entry, extrusion, and compartmentation are revi ewed, with a discussion of recent progress on the cloning and characterizat ion, directly in planta and in yeast, of some of the proteins involved in s odium transport. (C) 2000 Elsevier Science B.V. All rights reserved.