Physiological and antioxidant response of wheat (Triticum aestivum) seedlings to fluoroquinolone antibiotics

Combinations of antibiotics occur in terrestrial environments due to excessive prescription, consumption, and disposal and have adverse effects, including crop toxicity. We examined short-term (20-d) toxicity of the fluoroquinolone antibiotics ciprofloxacin, enrofloxacin, levofloxacin, and their mixture in a germination and a greenhouse sand culture study with wheat. We tested the hypothesis that oxidative stress plays a role in toxicity by examining stress products and antioxidants involved in detoxifying reactive oxygen species (ROS) during stress. Germination was unaffected by any antibiotic concentration or mixture used. The highest antibiotic concentrations, 100 and 300 mg L⁻¹, significantly decreased wheat growth. In 20 days exposure the maximum malondialdehyde production (2.45 μmol g⁻¹fresh weight), total phenols (16.40 mg g⁻¹of extract), and total antioxidant capacity (17.74 mg of Vitamin C g⁻¹of extract) and maximum activities of superoxide dismutase (7.99 units mg⁻¹protein min⁻¹) and ascorbate peroxidase (0.69 μmol ascorbate mg⁻¹protein min⁻¹) significantly increased compared to the control. In contrast, catalase (0.45 mmol H₂O₂mg⁻¹protein min⁻¹) and peroxidase (0.0005 units mg⁻¹protein min⁻¹) activity significantly decreased compared to the control. We conclude that high antibiotic concentrations in the plant growth medium reduced wheat growth by causing oxidative stress. The capacity to respond to oxidative stress was compromised by increasingly higher antibiotic concentrations in some enzyme systems. This stress damaged the physiological structure of the young plants and could reduce crop productivity in the long term. Consequently, fluoroquinolone-contaminated water challenges developing countries with constraints on available water for irrigation.