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partial pressure on nitrogen fixation in soybean using nitrogen isotopesHung, N. V. P.; 渡部 詩織*; 石川 伸二*; 大竹 憲邦*; 末吉 邦*; 佐藤 孝*; 石井 里美; 鈴井 伸郎; 河地 有木; 尹 永根; et al.
no journal, ,
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.
N and N isotope methods for the estimation of fixation and early distribution of nitrogen in soybean石井 里美; Nguyen Van Phi, H.*; 鈴井 伸郎; 河地 有木; 尹 永根; 大山 卓爾*; 藤巻 秀
no journal, ,
Various methods are used in the field of biological nitrogen fixation. In this study, we analyzed early dynamics of nitrogen fixation and subsequent transport in soybean by using radioactive and stable isotopes, N and N. N has an advantage for the analysis of kinetics and visualization, while N is beneficial for the analysis of distribution. N is the only practical radioisotope of nitrogen which has a very short half-life of only 9.97 min. In this study, we improved a rapid method to produce N with higher radioactivity and sufficient purity. We fed the tracer gas to the underground part of soybean plants for 10 min and collected the serial images for one hour by PETIS. As a result, we finally obtained the image of transport to the aerial part successfully. The stable isotope N has been widely used for the analysis of fixation and export. In this study, we fed N to the underground part of soybean plants for one hour and analyzed the time course of the distribution in the whole body. As a result, we found that about 10% of fixed nitrogen was exported from the root nodules in the initial one hour. From a methodological aspect, we concluded that the combination of N and N isotope is a strong tool for quantitative analysis of fixation and transport of nitrogen.
USDA110 generated by ion-beam irradiation武田 喜代子; 佐藤 勝也; 鳴海 一成*; 大津 直子*; 横山 正*
no journal, ,
With the aims of utilization as a biofertilizer inoculant and elucidation of high-temperature tolerance mechanism of soybean nodule bacteria, we had applied the ion beam breeding technology to a strain (
) USDA110. Consequently, we obtained a mutant named M14 which was able to maintain high viable cell numbers under high-temperature (42 degrees) for at least 7 days. Genome comparison with USDA110 revealed that (1) 1.27 Mbp inversion mutagenesis and (2) 18 single base mutations were occurred in M14. This study was the first attempt to apply the ion beam breeding technology to a prokaryote and succeeded in proving the effectiveness of it.