Real-time imaging of nitrogen fixation in an intact soybean plant

石井 里美; 鈴井 伸郎; 伊藤 小百合; 石岡 典子; 河地 有木; 大竹 憲邦*; 大山 卓爾*; 藤巻 秀

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To know kinetics of N fixation and transport of fixed N, a stable isotope, N has been widely used. However, it has experimental limitations to analyze a quick (rapid) response to environmental changes such as temperature or light conditions with this method because it is invasive. We have developed imaging technique by using nitrogen gas labeled with a radio isotope N (half life: 9.97 min), and PETIS (positron-emitting tracer imaging system) successfully, and we analyzed kinetics of fixation and fixed N quantitatively and noninvasively. In this study, we developed a rapid method to produce and purify N-labeled nitrogen gas. The gas was mixed with 10 ml of O and 5 ml of N and 35 ml of helium, and the gas mixture was used in the tracer experiment. The tracer gas was fed to the underground part of intact nodulated soybean plants and serial images of distribution of N were acquired by PETIS. The rates of nitrogen fixation of the six test plants were estimated as 0.170.10 mol N h from the dynamic data of PETIS images. The decreasing rates of assimilated nitrogen were also estimated as 0.0120.011 mol N h.