Translocation and accumulation of cadmium in cadmium-tolerant Polygonum thunbergii

Abstract

A cadmium (Cd)-tolerant Polygonum thunbergii H. Gross plant was chosen from among several wild plants, and its Cd location in tissues was analyzed. Absorption of Cd by P. thunbergii H. Gross plants cultured in a hydroponic solutuin showed the presence of a high Cd content in the stems similar to that found in the roots; however, the Cd content in the leaves was remarkably low and indicated the presence of a specific localized accumulation of Cd in the stems. On the other hand, P. thunbergii H. Gross plants, did not form Cd-binding peptides, such as phytochelatins or metallothioneins, with Cd treatment. These findings suggest that other compounds which are involved in, the detoxification mechanism of Cd are present in P. thunbergii H. Gross. A characteristic ninhydrin-positive compound was found in the xylem sap and stem squeezed juice. The results suggest that the binding of a ninhydrin-positive compound with Cd led to detoxification, followed by translocation and accumulation of Cd in the stems. Moreover, a mechanism whereby the translocation of Cd from stems to leaves was inhibited was postulated.