Interactions between Cd, Cu, and Zn influence particulate phytochelatin concentrations in marine phytoplankton: laboratory results and preliminary field data.

The effect of metal interactions on phytochelatin production by marine phytoplankton has received little attention but yet is critical to understanding the biochemical production of this potentially important metal-binding ligand in the field. Cd, Cu, and Zn additions were made singly and in combination to three species of laboratory cultures and to a natural algal assemblage from pristine coastal seawater. In the laboratory cultures intracellular phytochelatin varied with metal exposure and demonstrated metal- and concentration-dependent synergisms and antagonisms. Most notably, the addition of all three metals together greatly suppressed phytochelatin production in all cultures. Particulate phytochelatin was also measured at two field sites. In the field, phytochelatin production is related to ambient Cd, Cu, and Zn levels, and the deviations from the dose-response relationship are potentially explained by metal interactions similar to those observed in the laboratory cultures. Though particulate glutathione concentrations were very low in some field samples, it did not appear to limit phytochelatin production. Particulate phytochelatin concentrations in samples from both field sites were very similar to those measured in the laboratory cultures when exposed to all three metals together, and thus phytochelatin levels in the field may be regulated by the interaction of Cd, Cu, and Zn.