The Effect of Nitrate and Ammonium Nitrogen on the Free Amino Acid Composition of Tomato Plants and Tomato Fruit1

Abstract

Abstract The N form had a pronounced effect on the levels of free amino acids. When compared to NO 3 , NH 4 brought about a several fold increase in free amino acids (dry basis) in the roots, while smaller increases were observed in mature, fully expanded leaves, in young growing leaves, and in tomato fruit. Plants fed a combination of the 2 N forms had intermediate levels. The pattern of response to NH 4 indicated that aspartic and glutamic acids as well as their amides were predominantly snythesized in the roots when the N source was NH 4 . The site of synthesis shifted to the leaves when the N source was NO 3 . The amino acids arginine, serine, alanine, and γ-aminobutyric acid were predominantly synthesized in the leaves irrespective of N form. Topical application of Ca on fruit grown with NH 4 resulted in amino acid levels in the fruit similar to those of NO 3 fruit. Ammonium toxicity was found to be accompanied by large increases in the levels of GABA and serine in the leaves. It is suggested that ammonium toxicity is a manifestation of intracellular Ca deficiency.