Antioxidative stress responses in the floating macrophyte Lemna minor L. with cylindrospermopsin exposure

- We investigate the oxidative stress responses of Lemna minor to cylindrospermopsin.
- Cylindrospermopsin promotes oxidative stress at concentrations of 2.5 and 25 μg/L.
- Glutathione S-transferase, glutathione reductase and the carotenoids act together.
- L. minor has sufficient defence mechanisms in place against cylindrospermopsin.

Cylindrospermopsin toxicity and oxidative stress have been examined in aquatic animals, however, only a few studies with aquatic plants have been conducted focusing on the potential for bioaccumulation of cylindrospermopsin. The oxidative stress effects caused by cylindrospermopsin on macrophytes have not yet been specifically studied. The oxidative stress response of Lemna minor L. with exposure to cylindrospermopsin, was therefore tested in this study. The hydrogen peroxide concentration together with the activities of the antioxidant enzymes (catalase, peroxidase, glutathione reductase and glutathione S-transferase) were determined after 24 h (hours) of exposure to varying concentrations (0.025, 0.25, 2.5 and 25 μg/L) of cylindrospermopsin. Responses with longer exposure periods (48, 96, 168 h) were tested only with exposure to 2.5 and 25 μg/L cylindrospermopsin. Additionally, the content of the carotenoids was determined as a possible non-enzymatic antioxidant defence mechanism against cylindrospermopsin. The levels of hydrogen peroxide increased after 24 h even at the lowest cylindrospermopsin exposure concentrations. Catalase showed the most representative antioxidant response observed after 24 h and maintained its activity throughout the experiment. Catalase activity corresponded with the contents of hydrogen peroxide at 2.5 and 25 μg/L cylindrospermopsin. The data suggest that glutathione S-transferase, glutathione reductase and the carotenoid content act together with catalase but are more sensitive to higher concentrations of cylindrospermopsin and after a longer exposure period (168 h). The results indicate that cylindrospermopsin promotes oxidative stress in L. minor at concentrations of 2.5 and 25 μg/L. However, L. minor has sufficient defence mechanisms in place against this cyanobacterial toxin. Even though L. minor exhibits the potential to managing and control cylindrospermopsin contamination in aquatic systems, further studies in tolerance limits to cylindrospermopsin, uptake and experiments with prolonged exposure periods of more than 7 days are required.