Potassium nitrate application alleviates sodium chloride stress in winter wheat cultivars differing in salt tolerance

A sand culture experiment was conducted to answer the question whether or not exogenous KNO3 can alleviate adverse effects of salt stress in winter wheat by monitoring plant growth, K+/Na+ accumulation and the activity of some antioxidant enzymes. Seeds of two wheat cultivars (CVs), DK961 (salt-tolerant) and JN17 (salt-sensitive), were planted in sandboxes and controls germinated and raised with Hoagland nutrient solution (6 mM KNO3, no NaCl). Experimental seeds were exposed to seven modified Hoagland solutions containing increased levels of KNO3 (11, 16, 21 mM) or 100 mM NaCl in combination with the four KNO3 concentrations (6, 11, 16 and 21 mM). Plants were harvested 30 d after imbibition, with controls approximately 22 cm in height. Both CVs showed significant reduction in plant height, root length and dry weight of shoots and roots under KNO3 or NaCl stress. However, the combination of increased KNO3 and NaCl alleviated symptoms of the individual salt stresses by improving growth of shoots and roots, reducing electrolyte leakage, malondialdehyde and soluble sugar contents and enhancing the activities of antioxidant enzymes. The salt-tolerant cultivar accumulated more K+ in both shoots and roots compared with the higher Na+ accumulation typical for the salt-sensitive cultivar. Soluble sugar content and activities of antioxidant enzymes were found to be more stable in the salt-tolerant cultivar. Our findings suggest that the optimal K+/Na+ ratio of the nutrient solution should be 16:100 for both the salt-tolerant and the salt-sensitive cultivar under the experimental conditions used, and that the alleviation of NaCl stress symptoms through simultaneously applied elevated KNO3 was more effective in the salt-tolerant than in the salt-sensitive cultivar.