Induction of Oxidative Stress in the Red Macroalga <Emphasis Type="Italic">Gracilaria tenuistipitata</Emphasis> 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 (60%), 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 -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.