Glutathione and other low molecular weight thiols in marine phytoplankton under metal stress

Low molecular weight intracellular sulfhydryl-containing compounds are responsible for the intracellular detoxification of metals such as Cd and Cu in eucaryotic phytoplankton. Glutathione, the most abundant thiol in non-stressed cells (0.8 to 2.8 mM), chelates metals directly, and also serves as the biochemical precursor from which phytochelatins are synthesized. Very little is known about physiological variations in glutathione concentrations under conditions of metal stress or other environmental factors. We found that in response to steady-state Cd and Cu exposure, glutathione concentrations remain remarkably constant in all of the algae examined, even as phytochelatin concentrations increase by up to 100-fold control values (in some cases exceeding glutathione). In some species, γ-glu-cys and cysteine, precursors to glutathione, also increase significantly in response to metal exposure. Short-term exposure to Cd and Cu can have a dramatic effect on the intracellular glutathione and phytochelatin concentration especially when the culture is under nutrient limitation.