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. CO
was 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 N
h
(mean
SD) from the PETIS image data. The decreasing rates of assimilated nitrogen were also estimated as 0.012
0.011
mol N
h
(mean
SD).