PHYTOCHELATIN PRODUCTION BY MARINE-PHYTOPLANKTON AT LOW FREE METAL-ION CONCENTRATIONS - LABORATORY STUDIES AND FIELD DATA FROM MASSACHUSETTS BAY

Phytochelatins are small metal-binding polypeptides synthesized by alg ae in response to high metal concentrations. Using a very sensitive HP LC method, we have quantified phytochelatins from phytoplankton in lab oratory cultures at environmentally relevant metal concentrations and in marine field samples. Intracellular concentrations of phytochelatin , in the diatom Thalassiosira weissflogii, exhibit a distinct dose-res ponse relation with free Cd2+ concentration in the medium-not with tot al Cd2+-and are detectable even when the free Cd2+ concentration is le ss than 1 pM. In Massachusetts Bay, phytochelatin levels (normalized t o chlorophyll a) in the particulate fraction are similar to those meas ured in laboratory cultures exposed to picomolar free Cd2+ concentrati ons and exhibit a decreasing seaward trend. Incubations of natural sam ples with added Cd2+ confirmed the induction of the peptides by this m etal. Ambient phytochelatin concentrations thus appear to provide a me asure of the metal stress resulting from the complex mixture of trace metals and chelators in natural waters.