Cadmium is one of the most toxic trace metals and induces high concentrations of the metal-binding polypeptide phytochelatin, (γ-Glu- Cys)(n)Gly where n ≥ 2, in the marine diatom Thalassiosira weissflogii. Here we show that at high inorganic cadmium concentrations there is an efflux of cadmium from T. weissflogii so large that over half the cadmium taken up by the cell is returned to the medium. At high inorganic cadmium, there is also an efflux of phytochelatin from the cell. The efflux of both cadmium and phytochelatin stops when the external inorganic cadmium concentration is reduced. The efflux of phytochelatin and cadmium occurs at a molar ratio of approximately 4 γ-Glu-Cys subunits per cadmium, a stoichiometry similar to that measured in vivo for the cadmium-phytochelatin complex. We hypothesize that T. weissflogii exports the phytochelatin-cadmium complex as a detoxification mechanism. The cadmium-phytochelatin complex does not appear to be very stable in seawater once outside the cell since the cadmium exported is available to T. weissflogii and induces phytochelatin synthesis. Cadmium-phytochelatin export may be an important adaptive strategy that allows phytoplankton to survive in metal-polluted waters.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry