Abstract

To find why water hyacinth accumulates the toxic heavy metal ion Cd2+, the plant was cultivated in a mineral medium supplemented with Cd2+. Cd accumulated in the roots against the concentration gradient, mostly as a soluble form in the cytoplasm. Chromatography with Sephadex G-25 and G-50 columns showed that the accumulated Cd was present in two forms with mol wt of 2,300 and 3,000. The components carrying Cd showed a high ratio of absorbance at 254 nm to that at 280 nm, which suggests that they resemble mammalian Cd-thioneins. These components were not detected in the roots of water hyacinth cultivated in the absence of Cd2+, indicating that they are formed in response to the Cd2+ supplement.

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