Adaptation of plants to salt stress requires cellular ion homeostasis involving net intracellular Na+ and Cl？ uptake and subsequent vacuolar compartmentalization without toxic ion accumulation in the cytosol. Sodium ions can enter the cell through several low- and high-affinity K+ carriers. Some members of the HKT family function as sodium transporter and contribute to Na+ removal from the ascending xylem sap and recirculation from the leaves to the roots via the phloem vasculature. Na+ sequestration into the vacuole depends on expression and activity of Na+/H+ antiporter that is driven by electrochemical gradient of protons generated by the vacuolar H+-ATPase and the H+-pyrophosphatase. Sodium extrusion at the root-soil interface is presumed to be of critical importance for the salt tolerance. Thus, a very rapid efflux of Na+ from roots must occur to control net rates of influx. The Na+/H+ antiporter SOS1 localized to the plasma membrane is the only Na+ efflux protein from plants characterized so far. In this paper, we analyze available data related to ion transporters and plant abiotic stress responses in order to enhance our understanding about how salinity and other abiotic stresses affect the most fundamental processes of cellular function which have a substantial impact on plant growth development. 1. Introduction Agricultural productivity is severely affected by soil salinity. Environmental stress due to salinity is one of the most serious factors limiting the productivity of agricultural crops, most of which are sensitive to the presence of high concentrations of salts in the soil. There are two main components to salinity stress in plants; an initial osmotic stress and a subsequent accumulation of toxic ions which negatively affects cellular metabolism [1]. In addition, it can lead to secondary stresses such as nutritional imbalance and oxidative stress [2]. The Na+ cation is chaotropic and predominantly associated with the deleterious effect of salinity, and therefore, most research has focused on this mineral. However, plant adaptation to salt stress also requires appropriate regulation of Cl？ homeostasis [3]. Indeed, for species such as soybean, citrus, and grapevine where Na+ is predominantly retained in the roots and stems, Cl？ is considered more toxic since this ion is accumulated to high levels in shoot tissues, negatively impacting on essential processes such as photosynthesis. The osmotic component of salinity is caused by excess inorganic ions such as Na+ and Cl？ in the environment that decrease the osmotic potential of the soil
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