Nitrogen Metabolism

Abstract

The two years that have elapsed since the appearance of the last review on this subject (1) have witnessed a substantial increase in our knowledge the detailed biochemical pathways involved in nitrogen metabolism in plants. In addition, considerable information has accumulated on (a) the identification of hitherto unsuspected nitrogenous plant constituents; (b) the characterization of plant proteins; and (c) the nitrogen nutrition of plants, including studies on nitrogen fixation. These developments have been accompanied by the appearance of several interesting and important reviews. Of these, two new volumes from the McCollum-Pratt Institute must be singled out for special commendation. These reports of symposia on The Mechanism of Enzyme Action (2) and on Amino Acid Metabolism (3) continue the high standards of previous works and deserve the attention of all plant physiologists. Both contain provocative discussions on several aspects of nitrogen metabolism. In addition, singularly clear and comprehensive reviews on amino acid metabolism [Meister (4); Cohen (5); Greenberg (6)], on protein synthesis in animals [Borsook and in microorganisms [Gale (8)], and on the general topic of plant protein metabolism [Steward (9)] have appeared. It is obviously impossible to discuss adequately all of the recent advances in plant nitrogen metabolism. The author has, therefore, chosen for discussion four subjects of investigation in which he feels either that considerable progress has been made or that the outlook for future development is especially bright. These topics are (a) nitrate reduction, (b) amino acid metabolism, (c) amide peptide bond synthesis, and (d) protein synthesis.