Induction of oxidative stress in the red macroalga Gracilaria tenuistipitata by pollutant metals

Heavy metals are environmental pollutants that have the potential to induce severe stress-reactions in organisms on land as well as in the sea. We have studied effects of short term sublethal concentrations of copper (Cu2+) and cadmium (Cd2+) on the reactive oxygen metabolism of the marine red macroalga Gracilaria tenuistipitata. Additions of either 0.2 ppm Cu2+ or 1 ppm Cd2+ caused decreased growth (similar to60%), increased oxidation of lipids and increased oxidative damage to proteins as shown by increased content of protein carbonyl groups. Together this strongly suggests an induction of oxidative stress. Cu2+ caused more oxidative damage than Cd2+. As a response to the increased oxidative stress, addition of Cu2+ induced the activities of catalase, ascorbate peroxidase, and superoxide dismutase. In contrast, Cd2+ only caused increased catalase activity. Ten-fold lower concentrations of the metals did not cause an increase in enzyme activity. Both heavy metals also increased the content of the antioxidants beta-carotene and lutein. The results show that Cd2+ and, to a larger extent, Cu2+ induce oxidative stress in short-term experiments and the seaweed responds by increasing the activity of the reactive oxygen metabolism.