The ins and outs of intracellular ion homeostasis: NHX-type cation/H+ transporters

The biochemical characterization of cation/H+ exchange has been known since 1985 [1], yet only recently have we begun to understand the contribution of individual exchangers to ion homeostasis in plants. One particularly important class of exchangers is the NHX-type that is associated with Na+ transport and therefore salinity tolerance. New evidence suggests that under normal growth conditions NHXs are critical regulators of K+ and pH homeostasis and have important roles, depending on their cellular localization, in the generation of turgor as well as in vesicular trafficking. Recent advances highlight novel and exciting functions of intracellular NHXs in growth and development, stress adaptation and osmotic adjustment. Here, we elaborate on new and emerging cellular and physiological functions of this group of H+-coupled cation exchangers.