Real-time imaging of nitrogen fixation in an intact soybean plant with nodules using N-labeled nitrogen gas

Ishii, Satomi; Suzui, Nobuo; Ito, Sayuri; Ishioka, Noriko; Kawachi, Naoki; Otake, Norikuni*; Oyama, Takuji*; Fujimaki, Shu

Real-time images of nitrogen fixation in an intact nodule of hydroponically cultured soybean (Glycine max [L] Merr.) were obtained. In this study, we developed a rapid method to produce and purify N (half life: 9.97 min)-labeled radioactive nitrogen gas. N was produced from the O (p, ) N nuclear reaction. COwas filled in a target chamber and irradiated for 10 min with protons at energy of 18.3 MeV and electric current of 5 A which was delivered from a cyclotron. All CO in the collected gas was absorbed and removed with powdered soda-lime in a syringe, and replaced by helium gas. The resulting gas was injected into GC and separated, and 35 mL of fraction including the peak of [N]-nitrogen gas was collected by monitoring the chromatogram. The obtained gas was mixed with 10 mL of O and 5 mL of N and 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 obtained noninvasively using PETIS (positron-emitting tracer imaging system). The rates of nitrogen fixation of the six test plants were estimated as 0.17 0.10 mol Nh (mean SD) from the PETIS image data. The decreasing rates of assimilated nitrogen were also estimated as 0.012 0.011 mol Nh (mean SD).