Phytochelatin synthesis plays a similar role in shoots of the cadmium hyperaccumulator Sedum alfredii as in non-resistant plants

Phytochelatin (PC) synthesis is considered necessary for Cd tolerance in non-resistant plants, but roles for PCs in hyper-accumulating species are currently unknown. In the present study, the relationship between PC synthesis and Cd accumulation was investigated in the Cd hyperaccumulator Sedum alfredii Hance. PCs were most abundant in leaves followed by stems, but hardly detected by the reversed-phase high-performance liquid chromatography (HPLC) in roots. Both PC synthesis and Cd accumulation were time-dependent and a linear correlation between the two was established with about 1:15 PCs : Cd stoichiometry in leaves. PCs were found in the elution fractions, which were responsible for Cd peaks in the anion exchange chromatograph assay. About 5% of the total Cd was detected in these elution fractions as PCs were found. Most Cd was observed in the cell wall and intercellular space of leaf vascular cells. These results suggest that PCs do not detoxify Cd in roots of S. alfredii. However, like in non-resistant plants, PCs might act as the major intracellular Cd detoxification mechanism in shoots of S. alfredii.