NITROGEN METABOLISM OF CORN (ZEA MAYS) AS INFLUENCED BY AMMONIUM NUTRITION

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Abstract
N-de-pleted corn plants absorb N rapidly from complete nutrient solns. containing (NH4)2SO4 and increase in dry wt. In time studies in which the (NH4)2SO4 conc, was gradually increased to produce toxicity symptoms, injury to the leaves did not appear until the soluble N compounds in the expressed sap had reached high values. Symptoms of injury were necrotic areas on the leaf blades, tip burn, and a severe water deficit in the plant tops. Large amts. of glutamine, asparagine, residual a-atnino, and other forms of soluble N accumulated in the tops and roots. Ammonia did not increase in the tops until it had reached a high level in the roots. The pH of top and root sap increased slightly. Total sugars, sucrose, and protein detd. on dry material were not affected. Peptides and compounds that formed humin on acid-hydrolysis of de-proteinized sap make up a portion of the unidentified soluble N. Basic a-amino acids were only a very small part of the residual a-amino N synthesized. Alkaloid and unidentified soluble N remained constant during NH4+ absorption. Comparative rates of asparagine, glutamine, and residual a-amino N accumulation in roots and tops indicate that NH4+ is largely metabolized in the roots.