Mechanisms of Cl- transport contributing to salt tolerance

Mechanisms of Cl- transport in plants are poorly understood, despite the importance of minimizing Cl- toxicity for salt tolerance. This review summarizes Cl- transport processes in plants that contribute to genotypic differences in salt tolerance, identifying key traits from the cellular to whole-plant level. Key aspects of Cl- transport that contribute to salt tolerance in some species include reduced net xylem loading, intracellular compartmentation and greater efflux of Cl- from roots. We also provide an update on the biophysics of anion transport in plant cells and address issues of charge balance, selectivity and energy expenditure relevant to Cl- transport mechanisms. Examples are given of anion transport systems where electrophysiology has revealed possible interactions with salinity. Finally, candidate genes for anion transporters are identified that may be contributing to Cl- movement within plants during salinity. This review integrates current knowledge of Cl- transport mechanisms to identify future pathways for improving salt tolerance.