Uptake and transport of positron-emitting tracer (18F) in plants

The transport of a positron-emitting isotope introduced into a plant was dynamically followed by a special observation apparatus called ‘Positron-Emitting Tracer Imaging System’ to observe the damage and recovery functions of plants in vivo. In the system, annihilation γ-rays from the positron emitter are detected with two planar detectors (5 × 6 cm2). The water containing ca. 5 MBq/ml of 18F was fed to the cut stem of soybean for 2 min and then the images of tracer activity were recorded for 30–50 min. When the midrib of a leaf near the petiole was cut just before measurement, the activity in the injured leaf was decreased but detected even at the apex. This result suggests that the damaged leaf recovered the uptake of water through the lamina. Maximum tracer activities in leaves of unirradiated plant were observed within 10 min, whereas those of irradiated plant at 100 Gy were observed after over 25 min. The final activity of irradiated plant after 30 min was lower than that of unirradiated plant. In case of beans, there was a difference in the absorption behavior of the 18F-labeled water between unirradiated and irradiated samples. These results show that the system is effective to observe the uptake and transportation of water containing positron emitting tracer for the study of damage and recovery functions of plants.