Characterization of the high molecular weight Cd-binding complex in water hyacinth (Eichhornia crassipes) when exposed to Cd.

Water hyacinth ( Eichhornia crassipes) is a rapid-growing freshwater vascular plant that has been used to remove heavy metals in contaminated water. But the transportation and distribution of the absorbed heavy metal in the plant are not clear. In this study, water hyacinth was exposed to cadmium (Cd, 10 microM, pulse) and then transferred to a Cd-free solution (chase). The Cd content in the tissues was measured, and the Cd-binding complexes were isolated and identified. We found that (1) in two days, up to 80% of the Cd in the solution was absorbed by the plant, and the Cd could not be released back to the growth solution in the chase period; (2) approximately 1 mg of Cd was accumulated in the water hyacinth/g of dry weight in this condition; (3) invading Cd was bound rapidly as the low-molecular-weight (LMW) complex serving as the transient form for further sequestration; (4) the LMW complex in water hyacinth contained no phytochelatins and was different from the LMW complex in fission yeast; (5) the Cd absorbed in the plant was essentially stored in the high-molecular-weight (HMW) form after 1 week; (6) a small fraction of the absorbed Cd was found in the upper part of the plant (stem and leaves) in the form of complexes; (7) the HMW complex was composed of phytochelatins PC 3 and PC 4 primarily, with only a small amount of PC 2; (8) a rare PC-related peptide was found in the HMW complex that might be derived from PC 3. These observations contribute to the further understanding of water hyacinth in serving as an efficient and reliable accumulator for heavy metals.