THE ROLE OF REACTIVE OXYGEN SPECIES IN COPPER TOXICITY TO TWO FRESHWATER GREEN ALGAE(1)

The role of reactive oxygen species (ROS) in copper (Cu) toxicity to two freshwater green algal species, Pseudokirchneriella subcapitata (Korshikov) Hindák and Chlorella vulgaris Beij., was assessed to gain a better mechanistic understanding of this toxicity. Cu-induced formation of ROS was investigated in the two algal species and linked to short-term effects on photosynthetic activity and to long-term effects on cell growth. A light- and time-dependent increase in ROS concentrations was observed upon exposure to environmentally relevant Cu concentrations of 50 and 250 nM and was comparable in both algal species. However, effects of 250 nM Cu on photosynthesis were different, leading to a 12% reduction in photosynthetic activity in P. subcapitata, but not in C. vulgaris. These results indicate that differences in species-specific sensitivities measured as photosynthetic activity were not caused by differences in the cellular ROS content of the algae, but probably by different species-specific ROS defense systems. To investigate the role of ROS in Cu-mediated inhibition of photosynthesis, the ROS scavenger N-tert-butyl-α-phenylnitrone (BPN) was used, resulting in a reduction of Cu-induced ROS production up to control level and a complete restoration of photosynthetic activity of Cu-exposed P. subcapitata. This finding implied that ROS play a primary role in Cu toxicity to algae. Furthermore, we observed a time-dependent ROS release process across the plasma membrane. More than 90% of total ROS were determined to be extracellular in P. subcapitata, indicating an efficient method of cellular protection against oxidative stress.