Copper-induced changes of non-protein thiols and antioxidant enzymes in the marine microalga Phaeodactylum tricornutum

Abstract

The cellular defence mechanisms used by the marine diatom Phaeodactylum tricornutum to cope with copper toxicity were investigated. Copper induced a rapid synthesis of phytochelatins (PC) of different degree of polymerisation, initially formed at the expense of the cellular pool of glutathione. The formation of Cu–PC complexes was demonstrated by using size exclusion chromatography (SEC). These complexes were detected as early as 1 h after Cu exposure, and increased with time. Measurements of the activity of the antioxidant enzymes showed that superoxide dismutase (SOD) and CAT activity increased a few hours after Cu addition up to reach, after 48 h, the 40 and 200% of the control, respectively. Glutathione reductase (GR) activity, after an initial partial inhibition, also enhanced indicating the need to restore the oxidative balance of glutathione. APX and PPX activity was not significantly affected by Cu treatment, suggesting that in P. tricornutum CAT is the major enzyme for scavenging H2O2. The time course of Cu–PC complexes formation suggested that glutathione and its derived peptides (PC) form the first line of defence to combat against Cu-induced reactive oxygen species (ROS) formation. Thereafter, the activity of at least three antioxidant enzymes was enhanced to counteract the oxidative stress induced by Cu. Lipid peroxidation, measured as TBA-rm, enhanced after 24 and 48 h of exposure, indicating that prolonged Cu exposure induced membrane damage.