L4C-behavior ofl4C-[U]-sucrose,14C-[U]-asparagine, and14C-[U]-serine introduced to the flag leaf of rice and sorghum plants during ripening

Abstract

Abstract l4C-[U]-sucrose, 14C-[U]-asparagine, and 14C-[U]-serine were introduced from the tip of the flag leaf at the mid-ripening stage of rice and sorghum plants, which were grown without nitrogen application after flowering, and the 14C-behavior of the introduced 14C-compounds was studied. The results obtained were as follows. 1) When l4C-[U]-sucrose was introduced to the leaf, the amount of 14CO2 released by respiration from the leaf was larger under dark conditions than under light conditions in both crops. Since the amount of 14CO2 released by sorghum was smaller than that of rice under both light conditions, it was assumed that sorghum had reassimilated CO2 which was once released in the plant tissues. 2) When 14C-[U]-asparagine was introduced to the leaf, the amount of 14CO2 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 14C-asparagine was retained in sorghum, it was actively metabolized in rice. 3) When 14C-[U]-serine was introduced, the amount of 14CO2 released by respiration was larger under dark conditions than under light conditions in sorghum. The 14C of 14C-serine in rice was actively respired and used for the synthesis of sugar, especially under light conditions. 4) The 14C of each 14C-compound introduced was translocated into other organs more rapidly in rice than in sorghum. From the above results, it is considered that the 14C-compounds introduced to the vascular bundles were basically metabolized in a different manner in rice and sorghum, including the difference in the 14CO2 reassimilation rate and 14C translocation rate into other organs.