The effect of oxytetracycline on physiological and enzymatic defense responses in aquatic plant species Egeria densa,Azolla caroliniana,and Taxiphyllum barbieri

Oxytetracycline is an antibiotic widely employed in aquaculture to control and treat bacterial diseases of fish. Due to ineffective wastewater treatment, antibiotic residues from fish ponds are directly released into surface and groundwater affecting the environment. The Green Liver System® is a sustainable and cost-effective water treatment based on the ability of aquatic plants to biotransformation xenobiotics. To expand the application range of this system, Egeria densa, Azolla caroliniana, and Taxiphyllum barbieri were tested in response to oxytetracycline exposure. The aquatic plants were exposed to 0.5, 2.0, 5.0, and 25 μg/L oxytetracycline (n = 4) for 24 h in order to analyze the physiological responses (photosynthetic pigment contents and hydrogen peroxide formation -- H₂O₂), the biotransformation process (activity of glutathione S-transferase), and the antioxidant defense (glutathione reductase; peroxidase; and catalase) responses. There were no statistical differences in the photosynthetic pigment contents and H₂O₂ level between the treatment and control groups in the three aquatic plant species. It can be concluded that oxytetracycline does not provoke physiological damage to the tested species within 24 h of exposure. Nevertheless, the antioxidant defense mechanism was activated. Peroxidase and catalase were the most prominent antioxidant enzymes in the three plant species, whereas glutathione S-transferase activity was significantly increased in A. caroliniana and T. barbieri.