Department of Plant Sciences

We developed analytical methods for monitoring carbon translocation and nitrogen fixation in intact plants using short-lived radioactive tracer gas and the positron-emitting tracer imaging system (PETIS). In the analysis of carbon translocation, we fed ¹¹C (half life: 20.4 min)-labeled radioactive carbon dioxide gas to leaf blades of rice plants, and serial images of ¹¹C-photoassimilate were obtained non-invasively using PETIS. In order to understand source-sink relations, we manipulated source and sink strength by treating tested rice plants with p-chlorobenzenesulfonic acid (PCMBS), an inhibitor of sucrose transporters. We developed an analytical algorithm to estimate the velocity of ¹¹C-photoassimilate flow from the serial images. As a result, a decrease in the velocity after the manipulation was successfully detected. In the analysis of nitrogen fixation, we newly developed a rapid method to produce and purify ¹³N (half life: 10.0 min)-labeled radioactive nitrogen gas and fed the gas to the underground part of nodulated soybean plants. Serial images of distribution of ¹³N were obtained and obvious signal of ¹³N was observed at the nodules. To our knowledge, this is the first example of real-time imaging of nitrogen fixation in an intact plant.