Non-invasive estimation of phloem flow velocity under cadmium stress using the positron emitting tracer imaging system

Suzui, Nobuo; Kawachi, Naoki; Ishii, Satomi; Nakamura, Shinichi*; Matsuhashi, Shimpei; Fujimaki, Shu

In this study, we estimated a phloem flow under Cd stress using the positron emitting tracer imaging system (PETIS), quantitatively and non-invasively. In an experiment, CO was supplied to leaves of rice plants and the translocations of C-photoassimilates were monitored. We performed 6 sets of PETIS experiments using 56 different rice plants treated with 0, 1, 10, 100 M of Cd. The arrival times of C-photoassimilates to the basal region of each plant were analyzed. Phloem flow velocities were also estimated using the C-arrival time and the distance from the bottom of gas-cell to the basal region. Arrival time of 100 M Cd-treated plants was significantly different from that of control and 10 M Cd-treated plants (p 0.05). This result indicates that Cd exposure to the root for 1 day causes the decrease of phloem flow velocity in rice plant.