Accumulation and Distribution Characteristics of Zinc and Cadmium in the Hyperaccumulator Plant Sedum plumbizincicola

Accumulation and distribution of Zn and Cd in the hyperaccumulator plant Sedum plumbizincicola were investigated in a hydroponic experiment. Mean Cd and Zn concentrations in shoots (7,010 and 18,400 mg kg−1) were about sevenfold and fivefold higher than those in roots (840 and 3,000 mg kg−1) after exposure to 100 μM CdSO4 and 600 μM ZnSO4, respectively. Cd and Zn concentrations in young leaves (4,330 and 9,820 mg kg−1) were about sixfold and twofold higher than those in mature leaves (636 and 2,620 mg kg−1), respectively. MicroPIXE analysis showed that Zn was predominantly localized in epidermal cells in both young and mature leaves, but large amounts of Zn occurred in mesophyll cells in young leaves. Leaf tissue fractionation showed that soluble and cell wall fractions were different at the two stages of leaf growth. Young and mature leaves of S. plumbizincicola also showed different accumulation and distribution characteristics for Zn and Cd.