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

摘要

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.