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.