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Metabolism and Enzymology

Early Responses of Sodium-Deficient Amaranthus tricolor L. Plants to Sodium Application

Daisaku Ohta, Tru Matoh and Eiichi Takahashi

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

Effects of sodium application on sodium-deficient Amaranthus tricolor L. cv Tricolor seedlings were studied. Thirty-day-old A. tricolor seedlings grown without sodium received either 0.5 millimolar of NaCl or KCl, and the changes in the growth rate, chlorophyll concentration, photosynthetic oxygen evolution, and dark-oxygen consumption, and some enzyme activities were compared. Following the sodium treatment, the sodium concentration in the leaves increased from the initial value of 0.4 millimolar to 2 to 3 millimolar within 24 hours, and also the relative growth rate and O₂ evolution were enhanced within 24 hours. The stimulation of O₂ evolution was greater in the upper leaves than in the lower leaves. Although total chlorophyll concentration did not increase significantly, the increase in the chlorophyll a/b ratio was apparent within 24 hours. There were not significant increases in the C₄ photosynthetic enzyme activities; however, nitrate reductase activity increased by 350% by the sodium treatment within 24 hours, and this increase is considered not to be one of the consequences of the improved photosynthesis. Results suggest that the sodium treatment promoted CO₂ and nitrate assimilation resulting in the growth enhancement, and that sodium can be involved in some other functions than C₄ photosynthesis in A. tricolor plants.