Influence of the form of nitrogen on ammonium, amino acids and n‐assimelating enzyme activity in maize genotypes¹

Journal Paper No. 12863, the Agricultural Experiment Station, Purdue University, East Lafayette, IN 47907, USA. Research supported by a scholarship from CNPq ‐ Brazil.

Abstract

An understanding of nitrogen (N) interactions with plant growth and metabolism is important in order to increase the efficiency of fertilizer amendments for crop production. This study was initiated to evaluate the effect of the form of N and buffering with calcium carbonate (CaCO₃) on the activity of ammonium (NH₄) assimilating enzymes in a maize hybrid, a GDH‐deficient mutant, and the N6 normal inbred the mutant was derived from. Plants were grown in a growth chamber in sand culture with 10 mM of the different N forms [nitrate (NO₃), NH₄, ammonium nitrate (NH₄STO₃), and NH₄ plus CaCO₃). Hybrid plants grown in the unbuffered NH₄ were much smaller than those grown in NO₃ as the only source of N, but had comparable growth with each source of nitrogen if the pH was controlled. In contrast, a glutamate dehydrogenase‐deficient mutant (GDH) inbred and its normal control grew almost as well on both NH₄ treatments as on NO₃. GDH activity was higher in plants grown with NH₄ than NO₃, and it was almost nil in tissue of the GDH deficient mutant. Glutamine synthetase (GS) activity was lower in the unbuffered NH₄ treatment (acid pH) and increased significantly when CaCO₃ was added to the NH₄. Ammonium, as a sole source of N, induced a higher concentration of free ammonium and most free amino acids in plant tissues than NO₃.

Notes

Journal Paper No. 12863, the Agricultural Experiment Station, Purdue University, East Lafayette, IN 47907, USA. Research supported by a scholarship from CNPq ‐ Brazil.

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