DIFFERENCE IN SYSTEM OF CURRENT PHOTOSYNTHESIZED CARBON DISTRIBUTION TO CARBON AND NITROGEN-COMPOUNDS BETWEEN RICE AND SOYBEAN

(CO2)-C-14 was assimilated during 10 min in leaf of rice and soybean u nder 21 kPa O-2 (21% O-2 treatment) and 2 kPa O-2 (2% O-2 treatment) a t the vegetative growth stage and flowering stage. The C-14 distributi on ratio to respired CO2 and crude chemical components (sugars, polysa ccharides, amino acids, organic acids, and proteins) was determined. I n this paper, since emphasis was placed on the C-14 distribution mecha nism to carbon compounds and nitrogen compounds, the terms carbon meta bolism pool (C-pool) composed of sugars and polysaccharides, and nitro gen metabolism pool (N-pool) composed of organic acids, amino acids an d proteins were used. The results obtained were as follows. C-14 distr ibution ratio to N-pool at 0 min after C-14 assimilation was higher in soybean than in rice regardless of the treatments and stages, and tha t at 30 min after C-14 assimilation under light condition markedly dec reased both in rice and soybean. Therefore, especially in soybean, a l arge amount of photosynthesized C-14 was once distributed to the N-poo l, then C-14 compounds in the N-pool were reconstructed into the C-poo l. During this reconstruction process, C-14 compounds in the N-pool we re actively respired. C-14 distribution to N-pool at 0 min after C-14 assimilation changed slightly or did not change by the N treatment. C- 14 distribution to N-pool in the -N treatment of soybean (13-29 mg N g (-1) content in leaves) was higher than that in the +N treatment of ri ce (31-48 mg N g(-1) content in leaves). Photosynthesized carbon distr ibution to N-pool in rice decreased with growth, while it remained con stant in soybean. Accordingly, in soybean, photosynthesized carbon was predominantly distributed to the N-pool through photorespiration and/ or Calvin cycle (supplying triose-P), which was less affected by nitro gen nutrient and aging. Thus, the mechanism of photosynthesized carbon distribution to carbon and nitrogen compounds was basically regulated by inherited characters of each plant more than by the nitrogen statu s of leaves. By the 2% 0, treatment, C-14 distribution to N-pool decre ased in both crops regardless of N treatment, indicating that photores piration plays an important role in the supply of the preliminarily ph otosynthesized carbon compounds to N-pool. In the 2% O-2 treatment, C- 14 distribution to N-pool was higher in soybean than in rice, indicati ng that triose-P transported from chloroplast was preferentially distr ibuted to N-pool in the case of soybean.