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.