Department of Plant Sciences

We characterized the transport of cadmium (Cd) in soybean (Glycine max [L.] Merr.). A positron-emitting ¹⁰⁷Cd (half-life: 6.5 hr) tracer and a gamma-emitting ¹⁰⁹Cd (half-life: 453 d) tracer with non-radioactive Cd (final conc. 0.1 µM Cd) were fed as a mixture to the hydroponic culture. ¹⁰⁷Cd distribution in the intact test plants was imaged non-invasively using the positron-emitting tracer imaging system (PETIS). The test plants were sampled and separated to roots, stems, petioles, leaves, pods and seeds at about 2, 3 and 5 days after Cd feeding. After the sufficient decay of ¹⁰⁷Cd, ¹⁰⁹Cd accumulation in each part was analyzed and quantified using autoradiography and well-type counter. The PETIS images showed that the Cd reached shoot base about a few hours after feeding and was transported to upper nodes through the stem. The autoradiographic images revealed that a part of Cd was transported to the pods and seeds without passing through leaves within 2 days after Cd feeding. And the results obtained from well-type counter showed that a part of Cd absorbed by the roots moved and accumulated into the seeds, pods, leaves and petioles gradually within 5 days.