Change in allantoin and arginine contents in Dioscorea opposita 'Tsukuneimo' during the growth

The ureides, allantoin and allantoic acid, are believed to play an important role in the storage and translocation of nitrogen in higher plants. Arginine is a major component in the free amino acid pool in some plants. To investigate the behavior of ureides and free amino acids, especially arginine, in developing Dioscorea opposita plants 'Tsukuneimo', their contents as well as those of water and nitrogen in leaves, stems and tubers were quantitatively analyzed. The content of allantoin in the leaves decreased after any fertilization, while that in the stems did not increase after the 1st fertilization, 96 days after planting; it significantly increased after the 2nd fertilization, 26 days later. Allantoin content in tubers remained constant during tuber development. Arginine content in leaves and stems during the growth of 'Tsukuneimo' were lower than 0.15 and 4.8 μmol·g^-1FW, respectively. The time course of arginine in stems content was similar to that of allantoin. In tubers, arginine content at 170 days after planting increased to reach 14 times that at 142 days but then decreased, demonstrating that D. opposita transiently accumulates arginine in stems as well as allantoin in leaves and stems but only accumulates the latter in developing tubers.