THE METABOLISM OF NITROGEN IN THE LEAVES OF THE BUCKWHEAT PLANT

Abstract

Sir:In an experiment in which a preparation of ammonium chloride that contained nitrogen of atomic weight 15 was administered to buckwheat plants during a period of 47 hours, we have observed what appears to have been rapid replacement of the nitrogen of the leaf protein with the isotope.This replacement suggests that the physiologically active protein of the cells enters into reaction with the simple nitrogenous substances in the cell sap, and that continuous exchange takes place between the amino acids combined in the protein and these substances.The plants were grown from seed in a culture solution of the composition KHzPOd 0.00325 M, Ca(NO& 0.00215 M, MgSOc 0.00105 M, NH&l 0.0043 M, CaClz 0.00215 M, to which were added traces of boron, cobalt, manganese, and other heavy metals and 0.1 part per million of iron.The continuous drip technique of Shive was employed.At 29 days of age, when flowers were beginning to form, the plants were treated for 47 hours with a culture solution of the same composition in which the ordinary ammonium chloride was replaced by a sample that contained 1.2 atom per cent of N15 in excess of the normal isotope ratio.Leaf, stem, and roots were separately dried for analysis at 80' and the proximate components were separated by the methods of Vickery, Pucher, Wakeman, and Leavenworth (Connecticut Agric.Ezp.Stat., Bull.S99 (1937)).Isotope analysis of the nitrogen of the fractions gave the following: leaf protein 0.070, free ammonia of leaf 0.085, amide nitrogen of leaf 0.088 atom per cent excess.The ammonia nitrogen offered the plant during the experimental period was thus diluted only 17 times when it was introduced into the leaf protein and, accordingly, since little growth occurred, not less than 6 per cent of the protein nitrogen must