Effects of quinolone antibiotics stress on the germination of Monarda didyma under two photoperiods

The ecotoxicity of quinolone antibiotics has been established to be altered by photodegradation. In this study, we investigated the response of Monarda didyma seeds to different light conditions and treatment with quinolone antibiotics, and the tolerance of the plants under conditions of constant temperature and humidity. Initially, we assessed the effects of the typical quinolone antibiotics ciprofloxacin (CIP) and norfloxacin (NOR) on the germination and morphological indicators of M. didyma seeds and seedlings under 12 h·d⁻¹ light and 24 h·d⁻¹ darkness, and subsequently evaluated the tolerance of M. didyma seedlings using the membership function method. The results revealed that low concentrations of CIP promoted seed germination, whereas germination was inhibited by high concentrations of NOR. In addition, the vigor index values, radicle length, germ length, and fresh weight of seedlings were found to be negatively correlated with the concentration of antibiotics, with the length of radicles being established to be most sensitive to the toxic effects of quinolone antibiotics. CIP and NOR were found to have stronger inhibitory effects on germination and seedling morphology, respectively. With respect to light conditions, we found that M. didyma showed a stronger tolerance to NOR stress when exposed to 12 h·d⁻¹ of light. Furthermore, the germination potential, vigor index, radicle length, germ length, and fresh weight of M. didyma seeds and seedlings were shown to be significantly (P < 0.05) extremely significant (P < 0.01) negatively correlated with tolerance, and could accordingly serve as key indicators of the tolerance to quinolone antibiotics. Our findings in this study will provide an important reference for evaluation of the plant ecotoxicity of antibiotics and the antibiotic resistance of plants.