Thiol and Metal Contents in Perlphyton Exposed to Elevated Copper and Zinc Concentrations:A Field and Microcosm Study

摘要

Phytochelatins are metal-binding polypeptides produced by algae under metal exposure.The aim of this study was to investigate the effects of metal concentration variations in natural systems on periphyton at the biochemical level by analyzing its intracellular thiol content,in particular phytochelatins.To that purpose,two field campaigns were conducted in a stream subject to an increase of dissolved metal concentrations (particularly Cu and Zn) during rain events,which results in an increase of their accumulation in periphyton.At background metal concentrations,several thiols were detectable in periphyton,namely,glutathione (GSH),gamma-glutamylcysteine (gammaGluCys),phytochelatins (PC_2),and some unidentified thiols,U_1 and U_2.Glutathione and gammaGluCys contents were found to vary independently of the rain,as well as U_1 and U_2,whereas the phytochelatin content increased during the rain events.To investigate whether Cu or Zn may be responsible for this increase,microcosm experiments were carried out with natural water enriched with Cu,Zn,and Cd separately,and Cu and Zn in combination.In this study,GSH,PC_2,and U_1 were also detected,but not gammaGluCys.An increase in accumulated Cu content did not induce any changes in thiol content,whereas an increase of the Zn content induced a decrease in GSH content and an increase in phytochelatin content.Zinc ratherthan Cu may thus induce a phytochelatin content increase in periphyton in the field studies.Addition of Cu and Zn in combination also induced an increase in phytochelatin content.Cadmium was found to be the most effective inducer,with the production of larger phytochelatins (PC_(3-4)).This study is the first one to report changes in thiol content in periphyton in response to an increase of the metal concentration in natural freshwaters.