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Environmental and Stress Physiology

Sodium Stimulates Growth of Amaranthus tricolor L. Plants through Enhanced Nitrate Assimilation

Daisaku Ohta¹, Sumito Yasuoka, Tru Matoh and Eiichi Takahashi

Plant Nutrition Laboratory, Department of Agricultural Chemistry, Faculty of Agriculture, Kyoto University, Kyoto 606, Japan

Effects of Na application on the capacity of NO₃^– assimilation were studied in Na-deficient Amaranthus tricolor L. cv Tricolor plants. On day 30 after germination, Na-deficient A. tricolor plants received either 0.5 millimolar NaCl or KCl. The level of nitrate reductase activity doubled within 24 hours by the addition of Na and the enhanced level was maintained thereafter. When the plants were exposed to 2 millimolar ¹⁵NO₃^–, total ¹⁵N taken up by the plants was greater in the Na-treated plants than in the K-treated plants within 24 hours of the Na treatment. Incorporation of ¹⁵N into the 80% ethanol-insoluble nitrogen fraction of the Na-treated plants in the light period was about 260% of those of the K-treated plants indicating greater capacity of NO₃^– assimilation in the Na-treated plants. From these results, it was demonstrated that Na application to the Na-deficient A. tricolor plants promoted NO₃^– reduction and its subsequent assimilation into protein, resulting in growth enhancement.