Potassium-induced decrease in cytosolic Na⁺ alleviates deleterious effects of salt stress on wheat (Triticum aestivum L.)

Accumulation of NaCl in soil causes osmotic stress in plants, and sodium (Na⁺ ) and chloride (Cl^- ) cause ion toxicity, but also reduce the potassium (K⁺ ) uptake by plant roots and stimulate the K⁺ efflux through the cell membrane. Thus, decreased K⁺ /Na⁺ ratio in plant tissue lead us to hypothesise that elevated levels of K⁺ in nutrient medium enhance this ratio in plant tissue and cytosol to improve enzyme activation, osmoregulation and charge balance. In this study, wheat was cultivated at different concentrations of K⁺ (2.2, 4.4 or 8.8 mm) with or without salinity (1, 60 or 120 mm NaCl) and the effects on growth, root and shoot Na⁺ and K⁺ distribution and grain yield were determined. Also, the cytosolic Na⁺ concentration was investigated, as well as photosynthesis rate and water potential. Salinity reduced fresh weight of both shoots and roots and dry weight of roots. The grain yield was significantly reduced under Na⁺ stress and improved with elevated K⁺ fertilisation. Elevated K⁺ level during cultivation prevented the accumulation of Na⁺ into the cytosol of both shoot and root protoplasts. Wheat growth at vegetative stage was transiently reduced at the highest K⁺ concentration, perhaps due to plants' efforts to overcome a high solute concentration in the plant tissue, nevertheless grain yield was increased at both K⁺ levels. In conclusion, a moderately elevated K⁺ application to wheat seedlings reduces tissue as well as cytosolic Na⁺ concentration and enhances wheat growth and grain yield by mitigating the deleterious effects of Na⁺ toxicity.