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Root biomass of rice seedlings was increased at lower concentration or exogenous NHt, but it was decreased at higher concentration of exogenous NHt. The level or free NHt in the roots was accumulated gradually with the increase or NHt concentration in the nutrient solution. The content of the soluhle proteins was essentially constant at higher NHt. The activities of glutamine synthetase(GS), NADH-dependent gluta-mate synthase (NADH-GOGAT), and NADH-dependent glutamate dekydrogenase (NADH-GDH) were risen with exogenous NHt concentration at the lower NHt concentratlon range. But the activities of GS and NADH-GOGAT were decIined, and the level of NADH-GDH activity was kept constant under bigher NH concentration. The GS/GDH ratio suggested that NH was assimilated by GS-GoGAT cycle under lower NH concentration,but NADH-GDH was more important for NHt assimilation aud detoxifying NH to the tissue cells at the higher NH level. According to the growth and the activity changes of these ammonium-assimilat-ing enzymes of rice seedling roots, 10.0 μg/mL NH-N in nutrient solution was more suitable to the ricegrowth.
Root biomass of rice seedlings was increased at lower concentration or exogenous NHt, but it was decreased at higher concentration of exogenous NHt. The level or free NHt in the roots was accumulated with the increase or NHt concentration in the nutrient solution. The content of the activities of glutamine synthetase (GS), NADH-dependent gluta-mate synthase (NADH-GOGAT), and NADH-dependent glutamate dekydrogenase (NADH- GDH) were risen with exogenous NHt concentration at the lower NHt concentratlon range. But the activities of GS and NADH-GOGAT were decined, and the level of NADH-GDH activity was kept constant under highher NH concentration. The GS / GDH ratio suggested that NH was assimilated by GS-GoGAT cycle under lower NH concentration, but NADH-GDH was more important for NHt assimilation aud detoxifying NH to the tissue cells at the higher NH level. According to the growth and the activity changes of these ammonium- assimilat-ing enzymes of rice seedling roots, 10.0 μg / mL NH-N in nutrient solution was more suitable to the rice growth.