Plant salt tolerance and Na+ sensing and transport

Salinity is a global challenge to agricultural production. Understanding Na+ sensing and transport in plants under salt stress will be of benefit for breeding robustly salt-tolerant crop species. In this review, first, possible salt stress sensor candidates and the root meristem zone as a tissue harboring salt stress-sensing components are proposed. Then, the importance of Na+ exclusion and vacuolar Na+ sequestration in plant overall salt tolerance is highlighted. Other Na+ regulation processes, including xylem Na+ loading and unloading, phloem Na+ recirculation, and Na+ secretion, are discussed and summarized. Along with a summary of Na+ transporters and channels, the molecular regulation of Na+ transporters and channels in response to salt stress is discussed. Finally, some largely neglected issues in plant salt stress tolerance, including Na+ concentration in cytosol and the role of Na+ as a nutrient, are reviewed and discussed.