Redefining the role of sodium exclusion within salt tolerance.

Salt contamination of soils and irrigation water is a significant environmental concern for crop production. Leaf sodium (Na⁺) exclusion is commonly proposed to be a key subtrait of salt tolerance for many crop plants. High-Affinity Potassium (K⁺) Transporter 1 (HKT1) proteins have previously been identified as major controllers of leaf Na⁺ exclusion across diverse species. However, leaf Na⁺ exclusion does not always correlate with salt tolerance. We discuss literature which shows leaf Na⁺ accumulation can, in some circumstances, be tolerated without a detrimental effect on yield when HKT1 still functions to exclude Na⁺ from reproductive tissues. We conclude that, by having an ultimate role in the protection of reproductive performance, HKT1s' role in adaptation to salinity warrants redefinition.