Sodium efflux in plant roots: What do we really know?

Abstract

The efflux of sodium (Na+) ions across the plasma membrane of plant root cells into the external medium is surprisingly poorly understood. Nevertheless, Na+ efflux is widely regarded as a major mechanism by which plants restrain the rise of Na+ concentrations in the cytosolic compartments of root cells and, thus, achieve a degree of tolerance to saline environments. In this review, several key ideas and bodies of evidence concerning root Na+ efflux are summarized with a critical eye. Findings from decades past are brought to bear on current thinking, and pivotal studies are discussed, both "purely physiological", and also with regard to the SOS1 protein, the only major Na+ efflux transporter..