Sodium transporter protein, which plays a central role in plant tolerance to salt. Upon prolongated exposure to high concentrations, Na(+) translocates from the roots to the transpiring leaves where it can increase to toxic level. Involved in Na(+) recirculation from shoots to roots, probably by mediating Na(+) loading into the phloem sap in shoots and unloading in roots, thereby removing large amounts of Na(+) from the shoot. Does not transport K(+) but regulates K(+) nutrient status via its ability to facilitate Na(+) homeostasis. Probably not involved in root uptake of Na(+). Na(+)(in) = Na(+)(out) Highly expressed in roots. Expressed in flowers, leaves and stems. Expressed in the vascular tissues of every organs. In roots, leaves and flower peduncles, it is only expressed in the phloem tissues. Not expressed in root peripheral cells. N-glycosylated. Not essential for functional expression and membrane targeting. In contrast to K(+) channel proteins, it lacks a conserved Gly at position 68, explaining why it does not act as a K(+) transporter. Belongs to the TrkH potassium transport family. HKT (TC 2.A.38.3) subfamily.