Studies on Nitrogen Metabolism in Crop Plants : VII. The nitrogenous compounds in the bleeding sap and various organs of the crop plants

Abstract

The results obtained in the present study were summarized as follows. 1) The amount of nitrogen in the bleeding sap of the rice plant increased toward the early spikelet intiation stage and after that decreased rapidly to the boot stage. The relative composition of amino acids in the bleeding sap chiefly consisted of asparagine, alanine and glutamine, whereas aspartic acids, glutamic acid, valine, leucine and γ-aminobutyric acid were also found to occur in small amounts. Among these amino acids, especially asparagine and alanine disappeared sensitively reflecting the the nitrogen level in the rhizosphere ranging from the early spikelet intiation stage to the boot stage, and these amino acids increased considerably in the plant when nitrogenous fertilizer was supplied at the early spikelet initiation stage. However, a preponderance of alanine was recorded with additional nitrogen supply at the full heading stage, whereas asparagine and glutamine were absent after this stage. 2) A remarkable increase in response to the higher level of nitrogen supply was observed to occur in the main constituents of the soluble nitrogen, such as asparagine, alanine and glutamine (notably increase of asparagine and alanine being greater than that of glutamine) in leaf sheath plus culms of the rice plant, whereas not so much changes as described above were noted in those of the soluble nitrogen in the leaf blade, the relative amounts of aspartic acid, glutamic acid, alanine and γ-aminobutyric acid being constant. 3) The soluble nitrogenous compounds were also investigated in the bleeding sap and various organs of the hybrid sorghum with increasing levels of fertilizer nitrogen. The constituents of the soluble nitrogen in the bleeding sap such as asparagine showed a considerable increase in response to the increasing level of nitrogen, (particularly that of asparagine being greater than glutamine), and the same tendency was observed to exist in leaf sheath plus culms. On the other hand, in the leaf blade, the response to the nitrogen level was somewhat less conspicuous as compared with that of the bleeding sap and leaf sheath plus culms. From these facts, it was suggested that the diagnosis of nitrogenous nutrition in the crop plants might be made possible by detecting the amounts of amino acids particularly in the bleeding sap.