Analysis of the initial transport of fixed nitrogen and the effect of O partial pressure on nitrogen fixation in soybean using nitrogen isotopes
Hung, N. V. P.; Watanabe, Shiori*; Ishikawa, Shinji*; Otake, Norikuni*; Sueyoshi, Kuni*; Sato, Takashi*; Ishii, Satomi; Suzui, Nobuo; Kawachi, Naoki; Yin, Y.-G.; Fujimaki, Shu; Oyama, Takuji*
The quantitative analysis of initial transport of fixed nitrogen in intact nodulated soybean plants was conducted by the N pulse-chase experiment. Approximately 90% of fixed N was retained in the nodules and the N distribution in the basal nodules (78%) was higher than that of in the middle (12%) and distal nodules (0.1%) after 1 hour of stable isotope N exposure. The distribution of fixed N in the nodules decreased from 90% to 7% and increased in the other part during the initial 7 hours of the chase-period. The impacts of oxygen in rhizosphere on the symbiotic nitrogen fixation in real-time was evaluated under various O partial pressure. Soybean nodules were treated with mixed gas containing N labeled with a radioisotope N and various concentrations of O, and the nitrogen fixation activity in the nodules was visualized by the positron-emitting tracer imaging system (PETIS). The results showed that under normal condition the nitrogen fixation ability of soybean plant was higher compared to that of under the other conditions (0% O and 10% O). There was no significant difference in the nitrogen fixation activity between 0% O and 10% O.