Nitrogen Assimilating Enzyme Activity of Tomato Plant in Response to the Supply of Ammonium or Nitrate or Both

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The changes in the in vitro activity of nitrate reductase, glutamine synthetase and glutamate dehydrogenase of leaves and roots of tomato plant (Lycopersicon esculentum Mill.) with the supply of different nitrogen sources (ammonium, nitrate, or both) were examined. Nitrate reductase activity of leaves and roots became very low when nitrate was omitted from nutrient media. Plants supplied with ammonium nitrate had a detectable level of nitrate reductase activity. Glutamine synthetase activity increased similarly in roots of plants supplied with ammonium alone and of plants with ammonium nitrate, but it was not affected in leaves by the supply of different nitrogen sources. On the contrary, glutamate dehydrogenase activity was not clearly affected in roots by the supply of different nitrogen sources whereas it became much higher in leaves of plants supplied with ammonium alone and slightly higher in those of plants with ammonium nitrate than in those of plants with nitrate alone. It is considered that lower accumulation of ammonium in leaves of plants supplied with ammonium nitrate may be due to stimulation of metabolic steps other than the primary ammonia assimilation.
九州大学の論文