Effects of sulfur on accumulation, subcellular distribution and chemical forms of cadmium in hyperaccumulator-Sedum alfredii Hance

Differential centrifugation techniques and sequential chemical extraction method were used to study the effects of sulfur on accumulation, subcellular distribution and chemical forms of cadmium in hyperaccumulator-Sedum alfredii Hance. The results showed that Cd contents and amounts of Cd accumulated in leaves, stems and roots of Sedum alfredii Hance increased significantly with increasing S supplies from 1.5 to 2.25 mmol/L. The contents and percentage of Cd in roots, stems and leaves of hyperaccumulator-Sedum alfredii Hance decreased in the following pattern: cell wall (F1) soluble fraction (F3)cell organ and membrane (F2) and most of Cd was bound to the cell wall of hyperaccumulator-Sedum alfredii Hance. The contents of Cd in F1, F2, F3 fraction of root, stem and leaf of hyperaccumulator-Sedum alfredii Hance were increased and the change of percentage of Cd were different with increasing S supplies. As to Cd chemical forms, NaCl- ,acetic acid- and water-extractable Cd forms were dominant.With increasing S supplies, contents and percentages of NaCl- , acetic acid- and water-extractable Cd forms in root, NaCl- and acetic acid- extractable Cd forms in stem were increased, but ethanol- and HCL- extractable Cd forms in root and water-,ethanol- and HCL- extractable Cd forms in stem were decreased. Increasing S supplies enhanced contents of NaCl- and acetic acid- water- extractable Cd forms in leaf, but little effect on their ercentages.