Combination of N and N isotope methods for the estimation of fixation and early distribution of nitrogen in soybean

Ishii, Satomi; Nguyen Van Phi, H.*; Suzui, Nobuo; Kawachi, Naoki; Yin, Y.-G.; Oyama, Takuji*; Fujimaki, Shu

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.