C-14 BEHAVIOR OF C-14 [U]-SUCROSE, C-14 [U]-ASPARAGINE, AND C-14 [U]-SERINE INTRODUCED TO THE FLAG LEAF OF RICE AND SORGHUM PLANTS DURING RIPENING

C-14-[U]-sucrose, C-14-[U]-asparagine, and C-14-[U]-serine were introd uced from the tip of the flag leaf at the mid-ripening stage of rice a nd sorghum plants, which were grown without nitrogen application after flowering, and the C-14-behavior of the introduced C-14-compounds was studied. The results obtained were as follows. 1) When C-14-[U]-sucro se was introduced to the leaf, the amount of (CO2)-C-14 released by re spiration from the leaf was larger under dark conditions than under li ght conditions in both crops. Since the amount of (CO2)-C-14 released by sorghum was smaller than that of rice under both light conditions, it was assumed that sorghum had reassimilated CO2 which was once relea sed in the plant tissues. 2) When C-14-[U]-asparagine was introduced t o the leaf, the amount of (CO2)-C-14 released by respiration from the leaf under light conditions was similar to that under dark conditions in rice, but it was larger under dark conditions in sorghum. Although a large amount of C-14-asparagine was retained in sorghum, it was acti vely metabolized in rice. 3) When C-14-[U]-serine was introduced, the amount of (CO2)-C-14 released by respiration was larger under dark con ditions than under light conditions in sorghum. The C-14 of C-14-serin e in rice was actively respired and used for the synthesis of sugar, e specially under light conditions. 4) The C-14 of each C-14-compound in troduced was translocated into other organs more rapidly in rice than in sorghum. From the above results, it is considered that the C-14-com pounds introduced to the vascular bundles were basically metabolized i n a different manner in rice and sorghum, including the difference in the (CO2)-C-14 reassimilation rate and C-14 translocation rate into ot her organs.