Studies on Nitrogen Metabolism in Crop Plant : V. Changes of the nitrogenous compounds in the rice plant during ageing

Abstract

The nitrogen compounds of the rice plant, which was supplied with nitrogen at the early spikelet initiation stage and the full heading stage, respectively, were investigated to manifest the nitrogen metabolism during ageing. The main results may be summarized as follows: 1) During the period from the early tillering stage to the full heading stage, the protein and RNA levels in the leaf blade increased largely accompanying with high level of the soluble nitrogen, whereas in the ripening period, the protein and RNA levels decreased rapidly in spite of high level of the soluble nitrogen, on the plant supplied with nitrogen at the two different growth stages. 2) Especially in the leaf sheathes and culm the soluble nitrogen responded strikingly to the nitrogen supply and accumulated largely in these organs, whereas in the leaf blade the soluble nitrogen not so much increased as the protein, before heading stage. Accordingly, it was clear that the protein level in the leaf blades was correlated intimately with the levels of soluble nitrogen in the leaf sheathes and culms during growth except the ripening period, in which the protein and RNA level decreased. 3) In the leaf blade, aspartic acid, glutamic acid, alanine, asparangine and glutamine were predominantly present as compared with valine, leucine, proline and arginine, in the free amino acids at the early tillering stage. The relative composition of these amino acid was not essentially chaged before heading stage even by the nitrogen supply, because protein assimilation proceeded rapidly in these periods However, in the ripening period, valine, leucine and proline appeared in larger amounts in the plants supplied with nitrogen at the two stages mentioned above. Similarly, in the detached leaves, larger amounts of valine, leucine and proline appeared during senescence accompanying with the protein breakdown. Therefore, changes of the free amino acids content in the ripening period well agreeded with changes of those in the detached leaves. 4) In the leaf sheathes and culms, on the other hand, alanine, asparagine and glutamine were predominantly present, and asparagine was richer than glutamine at the early tillering stage. These free amino acids decreased rapidly in amounts from the early spikelet initiation stage to the boot stage, and tended to increase largely in the plant supplied with nitrogen at the early spikelet initiation stage. However, in the ripening period, arginine and proline as compared with asparagine and glutamine predominantly appeared in the plant supplied with nitrogen especially at full heading stage.