ROS as a key player in quinolone antibiotic stress on Arabidopsis thaliana: From the perspective of photosystem function, oxidative stress and phyllosphere microbiome

With the increasing use of antibiotics, their ecological impacts have received widespread attention. However, research on the toxicity of quinolone antibiotics is still limited, especially regarding the oxidative stress and phyllosphere of plants. In this study, the toxic effects of enrofloxacin, norfloxacin, and levofloxacin on Arabidopsis thaliana and their underlying mechanisms were investigated. The toxicity of the three quinolone antibiotics decreased in the following order: enrofloxacin > norfloxacin > levofloxacin. Physiological cellular changes, such as plasmolysis and chloroplast swelling, were observed using electron microscopy. Photosynthetic efficiency was inhibited with a decline in the effective photochemical quantum yield of photosystem II (Y(II)) and non-photochemical quenching (NPQ), indicating that quinolone antibiotics might reduce light energy conversion efficiency and excess light energy dissipation. Oxidative stress occurred in A. thaliana after quinolone antibiotic treatment, with an increase in reactive oxygen species (ROS) levels and malondialdehyde (MDA) content. High ROS levels stimulated the over-expression of superoxide-responsive genes for self-protection. Structural equation modeling (SEM) analysis showed that photosynthesis inhibition and cellular damage caused by oxidative stress were critical factors for growth inhibition, suggesting that the antioxidant response activated by ROS might be a potential mechanism. Furthermore, the diversity of the phyllospheric microbial communities decreased after enrofloxacin exposure. Additionally, specific microbes were preferentially recruited to the phyllosphere because of the higher ROS levels.