Studies on Nitrogen Metabolism in Crop Plants

Abstract

Using two soybean varieties, Harosoy and Tosan No.89, which were contrasting in growth habit, the author examined the relationship between the photosynthetic activity of leaves and nitrogen metabolism with reference to leaf growth. The results obtained are summarized as follows:1. Harosoy had far less leaf area than Tosan No.89. In the case of Harosoy, leaf area decreased with the reduction of light intensity under which the plants had been grown. In the case of Tosan No.89, the leaf area development was rather promoted by moderate shading.2. Harosoy showed higher photosynthetic activity compared with Tosan No.89 when they had been grown under full natural light. However, in the case of the former variety, photosynthetic activity distinctly decreased with the reduction of light intensity during the growing period. By contrast, in Tosan No.89, shading treatment did not necessarily bring about depression of photosynthetic activity so long as it was not very severe. Such variations in photosynthetic activity with variety and light condition were associated with the parallel variations in soluble proteins and fraction-1 protein.3. TIBA spraying resulted in depression of leaf expansion and increase of photosynthetic activity. Such a variation in photosynthetic activity was associated with the parallel variations in total-N. protein-N, soluble protein and non protein-N. The effects of TIBA as described above were especially remarkable under the conditions in which leaf expansion was large, i.e., in variety Tosan No.89 and under shading treatment.4. From these results, it was suggested that the photosynthetic activity of leaves is regulated through protein metabolism, and this, in turn, is under the control of hormons which are concerned with leaf expansion.