Evaluating Phytotoxic Effects of Chlortetracycline Following Uptake by Pinto Bean and Corn Plants.

Tetracycline antibiotics, such as chlortetracycline (CTC) and tetracycline (TC), are introduced into agricultural lands through the application of manure as fertilizer. In this study, phytotoxicity of CTC on pinto beans (Phaseolus vulgaris) and maize (Zea mays) was investigated under controlled conditions. When grown in CTC-treated soil, a significant increase in the activities of the plant stress proteins glutathione S-transferases (GST) and peroxidases (POX) were observed in maize plants, but not in pinto beans. In vitro conjugation reactions demonstrated that the induced GST in maize catalyzed the conjugation of glutathione (GSH) with CTC, producing stable conjugates that were structurally characterized using liquid chromatography/mass spectrometry (LC/MS). Our results suggest that maize is able to detoxify CTC via the glutathione pathway, whereas pinto beans cannot. While the mechanism of this toxicity is not yet understood, CTC is known to be a calcium chelator. We describe here a novel method to show that CTC is taken up by Pinto beans plants and chelates calcium in leaves. Our findings provide evidence that chelation of intracellular calcium by CTC is related to phytotoxic effects caused by this antibiotic in Pinto beans. Root uptake of CTC and TC by Pinto beans and their translocation to leaves were further verified by fluorescence spectroscopy and LC/MS. This study demonstrates the importance of plant uptake in determining the fate of antibiotics in soil and their potential phytotoxicity to susceptible plants.