Sodium transport in plants: a critical review

Abstract

Summary: Sodium (Na) toxicity is one of the most formidable challenges for crop production world‐wide. Nevertheless, despite decades of intensive research, the pathways of Na+entry into the roots of plants under high salinity are still not definitively known. Here, we review critically the current paradigms in this field. In particular, we explore the evidence supporting the role of nonselective cation channels, potassium transporters, and transporters from the HKT family in primary sodium influx into plant roots, and their possible roles elsewhere. We furthermore discuss the evidence for the roles of transporters from the NHX and SOS families in intracellular Na+partitioning and removal from the cytosol of root cells. We also review the literature on the physiology of Na+fluxes and cytosolic Na+concentrations in roots and invite critical interpretation of seminal published data in these areas. The main focus of the review is Na+transport in glycophytes, but reference is made to literature on halophytes where it is essential to the analysis. ContentsSummary54I.Introduction55II.The role of nonselective cation channels in primary sodium influx – a solid consensus. How solid is the evidence?55III.Low‐affinity cation transporter 1 – a forgotten link?61IV.Are potassium transporters implicated in sodium influx?62V.HKT: a saga of twists and turns – where do we stand?64VI.SOS: an ambiguous tale67VII.Vacuolar storage via NHX: some lingering questions68VIII.Other pathways – the apoplast and possibilities of symport with chloride69IX.‘Toxic’ Na+fluxes, Na+‘homeostasis’, and the question of cytosolic Na+71X.Concluding remarks72Acknowledgements73References73