Abstract
To study the transport mechanism of cadmium (Cd), the route of Cd from root to shoot was visually identified by employing a radioisotope tracer, 109Cd. The radioactive Cd solution (2MBq/10ml 0.1μM CdCl2) was supplied from the root of a rice seedling with emerging 6th leaf for 15 minutes and exposed to an imaging plate (IP). It was found that Cd was directly transported from root to the youngest 6th leaf. To compare the feature of Cd transport with those of P, S and Ca, radiographs of 32P, 35S and 45Ca were also taken. The result showed that the initial accumulation pattern of Cd was similar to that of Ca. To understand the transport route of Cd more clearly, 109Cd tracer was supplied to one root which was developed from one internode. The internode was successively sliced and was exposed to an IP to get sequential distribution of 109Cd. From the radiographs, it was suggested that Cd was transferred to phloem in the very early stage of transport from the root. During the upward transportation in the stem, only a small amount of Cd was distributed to the small vascular bundles oriented to the leaf. The transport pathway of Cd will be explained and discussed.
