Noninvasive imaging of nitrogen fixation by soybean nodules

Abstract

¹⁵N, a stable isotope, has long been used in studies about kinetics of nitrogen fixation and transport of the fixed nitrogen. However, it is difficult to analyze instant responses to an environmental (ex. temperature, light conditions) change with this method because it requires invasive assay. In this study, we have developed a method to produce ¹³N-labeled radioactive nitrogen gas (¹³N₂) with high purity. We fed the ¹³N₂ mixed with defined concentrations of O₂ and N₂ to the underground part of nodulated soybean plants and obtained movies of fixation of nitrogen gas using PETIS (positron-emitting tracer imaging system) successfully. The rates of fixation within 10 min were estimated quantitatively.