Plant Cd2+ and Zn2+ status effects on root and shoot heavy metal accumulation in Thlaspi caerulescens

Abstract

• In this study we address the impact of changes in plant heavy metal, (i.e. zinc (Zn) and cadmium (Cd)) status on metal accumulation in the Zn/Cd hyperaccumulator, Thlaspi caerulescens. • Thlaspi caerulescens plants were grown hydroponically on both high and low Zn and Cd regimes and whole-shoot and -root metal accumulation, and root 109Cd2+ influx were determined. • High-Zn-grown (500 μm Zn) plants were found to be more Cd-tolerant than plants grown in standard Zn conditions (1 μm Zn). Furthermore, shoot Cd accumulation was significantly greater in the high-Zn-grown plants. A positive correlation was also found between shoot Zn accumulation and increased plant Cd status. Radiotracer 109Cd root flux experiments demonstrated that high-Zn-grown plants maintained significantly higher root Cd2+ influx than plants grown on 1 μm Zn. It was also found that both nickel (Ni) and copper (Cu) shoot accumulation were stimulated by high plant Zn status, while manganese (Mn) accumulation was not affected. • A speculative model is presented to explain these findings, suggesting that xylem loading may be one of the key sites responsible for the hyperaccumulation of Zn and Cd accumulation in Thlaspi caerulescens.