Role of sodium proton antiporters in cellular homeostasis of plants under abiotic stress conditions

Soon after discovery, immense work has been carried out on biochemical characterization and functional validation of plant sodium-proton (Na+/H+) antiporters (NHXs). NHXs are integral membrane proteins localized at the various membranes of a plant cell, including endomembrane compartments and plasma membrane. Transgenic model and crop plants, overexpressing NHXs isolated from both glycophytes and halophytes, were developed and well-studied for their role in abiotic stress tolerance, especially in salt and drought stress. NHXs exchange Na+ and K+ with H+ ions by using proton motive force generated by plasma membrane H+ PPase, located at the plasma membrane and tonoplast, respectively. NHXs execute the inevitable process of pH and Na+/K+ ion homeostasis in plants during normal growth condition and also under abiotic stresses. Apart from this, NHXs are found to be involved in the regulation of cell physiology, osmotic adjustments, cell turgor maintenance, protein processing and trafficking, microtubule organization, and the development of roots, embryo, and flowers. Recently, T-DNA insertional mutants and gene knockout studies clearly show the role of NHXs in abiotic stress tolerance with characteristics like altered leaf growth and decrease in epidermal cell frequency, leaf surface area, root cell size in the transition zone, and stomatal functions. As a consequence, it can be concluded that NHXs antiporters play a crucial role in the cellular homeostasis of plants under abiotic stresses.