Arabidopsis NHX Transporters: Sodium and Potassium Antiport Mythology and Sequestration During Ionic Stress

Abstract

A crucial prerequisite for plant growth and survival under high salinity is maintenance of Na+ and K+ balance. Accumulation of Na+ and K+ in high concentration in the cytosol reduces crop yield. To cope with such imbalance ionic conditions, plants use a number of transporters to maintain Na+ and K+ homoeostasis inside the cell and regulate plant growth and development. This cation and pH homoeostasis is regulated by monovalent cation/proton antiporters (CPA) that fall in two categories, the CPA1 family that includes Na+/H+ NHX antiporters, and the CPA2 family that includes Cation/H+ (CHX) and K+ efflux antiporters (KEA). In this review we highlighted the role of NHX-antiporters in regulation of Na+ and K+ balance. NHX proteins are required for accurate K+ compartmentation. They mediate K+ specific vacuolar sequestration, pH adjustment, turgor and osmotic regulation, and play a unique role in stomatal movement and cell expansion.