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Report No.

Evaluation of velocity of $$^{11}$$C-photoassimilate flow using positron-emitting tracer imaging system

Suzui, Nobuo; Kawachi, Naoki; Ishii, Satomi; Yin, Y.-G.; Iwasaki, Aya*; Ogawa, Kenichi*; Fujimaki, Shu

In this study, we developed an analytical method to evaluate velocity of photoassimilate flow using $$^{11}$$C-tracer and the positron-emitting tracer imaging system (PETIS). $$^{11}$$CO$$_{2}$$ gas tracer was fed to the compound leaves of the soybean plant, and serial images of $$^{11}$$C distribution were obtained by PETIS. Regions of interests (ROIs) were set in the node of the first compound leaf (ROI-1) and the stem base (ROI-2). Time course of $$^{11}$$C-radioactivity (Time-Activity Curve: TAC) in each ROI was generated from the serial images. Initial slope of the rising $$^{11}$$C-radioactivity was estimated by a linear least-square method using the TAC data. The value of the intercept of approximated line to the background line (X-intercept) was defined as "$$^{11}$$C-arrival time" to the ROIs. In order to determine X-intercept with a fair criterion, we developed an analytical program. The velocities of $$^{11}$$C-photoassimilate flows of 18 individual soybean plants were estimated by the values of $$^{11}$$C-arrival time and the distance between ROI-1 and ROI-2. As a result, the average value of the velocity was 113 cm h$$^{-1}$$ and the standard deviation was 20 cm h$$^{-1}$$. This result indicates the newly developed method is a reliable tool for the quantitative analysis of photoassimilate flow through the phloem.



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