Sodium transport in plant cells

Salinity limits plant growth and impairs agricultural productivity. There is a wide spectrum of plant responses to salinity that are defined by a range of adaptations at the cellular and the whole-plant levels, however, the mechanisms of sodium transport appear to be fundamentally similar. At the cellular level, sodium ions gain entry via several plasma membrane channels. As cytoplasmic sodium is toxic above threshold levels, it is extruded by plasma membrane Na+/H+ antiports that are energized by the proton gradient generated by the plasma membrane ATPase. Cytoplasmic Na+ may also be compartmentalized by vacuolar Na+/H+ antiports. These transporters are energized by the proton gradient generated by the vacuolar H+-ATPase and H+-PPiase. Here, the mechanisms of sodium entry, extrusion, and compartmentation are reviewed, with a discussion of recent progress on the cloning and characterization, directly in planta and in yeast, of some of the proteins involved in sodium transport. (C) 2000 Elsevier Science B.V. All rights reserved.