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Antibiotics have been identified as a new type of environmental contaminant because of their increased use in farm animal production systems. Those drugs that animals are not absorbed mostly are excreted in the feces and urine and contaminates soils. However, the effects of antibiotics on crop plants are still largely unknown. In this study, we determined the effects of chlortetracycline (CTC), a veterinary drug released into the agricultural field by grazing animals or through manure application, on the growth and physiology of Brassica campestris seedlings. Differently from animals, Brassica campestris seedlings have accumulated 5-10-fold higher CTC during cultivation rather than excretion. Morphologically, CTC delays seed germination and inhibits seedling growth such as shortening primary root length and decreasing chlorophyll level. At the molecular level, CTC accumulation in plants downregulated the expression of superoxide dismutase (SOD) genes and decreased the production of hydrogen peroxide (H 2 O 2). Since H 2 O 2 is one of the signaling components involved in the regulation of root growth, exogenous application of H 2 O 2 partially restored the growth and physiology of CTC-treated seedlings. These results suggest that application of CTCcontaining manure or compost to soil delays seed germination and inhibits plant growth.

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