Studies on Nitrogen Metabolism in Crop Plants : XVI. Changes in photosynthesis and nitrogen metabolisem in relation to leaf area growth of several rice varieties

Abstract

Using several rice varieties of rice ecotypes, Aman, Aus, Bulu and Tjereh, including Japonica varieties, it was attempted to clarify the relationships between the leaf area growth, light-saturated photosynthetic rate and soluble protein level, and furthermore to investigate the assimilation of ¹⁵N-labelled ammonium nitrogen into the protein fractions in the leaf blades: The results obtained are as follows: 1. In the eleven rice varieties, it was found that there was negative association betwecn single leaf area and light-saturated photosynthetic rate per unit leaf area. 2. The contents of soluble protein per unit leaf area in the leaf blades of the varieties which developed smaller single leaf area were much higher than those of the varieties which developed larger single leaf area. Accordingly, there existed strong negative association between single leaf area and soluble protein content in the leaf blades. This, in turn, appeared to being about the negative correlation between single leaf area and photosynthetic rate as described above. 3. The assimilation of ¹⁵N-labelled ammonium nitrogen was studied in the five rice varieties which were contrastive in the leaf area growth. As a result, it was concluded that fraction-1 protein among soluble proteins was accumulated greatly in the leaf blades of the varieties which developed smaller single leaf area as compared with those of the varieties which did larger single leaf area, because protein synthesis predo-minated over protein degradation in the upper leaf blades and protein degradation was suppressed greatly in the lower leaf blades.