Response of ammonium assimilation enzymes to nitrogen form treatments in different plant species1

Abstract This series of experiments studied N metabolism in tomato, rice and corn. Ammonium (NH4 +), as a sole source of N, reduced tomato and corn growth, but not rice growth. Tomato showed the most severe NH4 + toxicity. Ammonium assimilation enzyme activity differed greatly among the species. Rice had much higher glutamine synthetase (GS) activity than corn and tomato with NH4 + nutrition. GS activity was especially high in shoot tissue. Ammonium induced high activity of glutamate dehydrogenase (GDH) in roots of tomato but not in rice. GS activity in rice increased as the level of NH4 + increased; and it was higher in shoots than roots, indicating GS activity as a key factor in the detoxification and metabolism of NH4 + in green tissues of efficient plant species. Notes Research supported by a scholarship from CNPq ‐ BRAZIL. Journal Paper No. 11,295. The Agricultural Experiment Station, Purdue University, West Lafayette, IN 47907