## 3 Results and Discussions
### Detoxification of VAs  
In this study, we failed to detect the metabolites of the active molecules SDZ and OTC in the plant samples. Some possible reasons for this can be  
Figure 1: Uptake of veterinary antibiotics (VAs) by different parts of lettuce, carrot, and pepper grown in soil treated with VAs. Error bars represent standard error. Concentration values followed by different letters are significantly different (\(p<0.05\)) according to [PERSON]’s multiple range test. SDZ = Sulfadimethoxine; OTC = Oxytterracycline; STR = Streptomycin.  
* Metabolites not formed during the experimental period.
* Metabolites formed are processed by the plant detoxification system and were beyond the detection limit (at the time of analysis).  
The phase I (CPR) and phase II (GST) detoxifying enzymes, of the plant detoxification system, were analyzed. The activity of the CPR enzyme increased with increasing concentration of SDZ and OTC antibiotics in the soil-manure mixture, irrespective of the plant type (Figure 2). On the other hand, there was no significant difference between control and STR antibiotic. CPR enzyme activity ranged from 3.69 to 9.17, 1.69 to 4.70, and 6.98 to 10.47 mmol min\({}^{-1}\) for lettuce, carrot, and pepper, respectively. CPR enzymes function to metabolize potentially toxic compounds, including drugs. Therefore, increased CPR enzyme activity signifies the onset of detoxification mechanism or the increase in metabolic activity. A previous study has reported the induction of CPR activity in Oryza sativa exposed to the herbicide atrazine [27]. The five-liganded heme-proteins of cytochromes P450 can exist as many isoforms, which enables them to accommodate a wide range of substrates and catalyze a variety of reactions [28]. However, we were unable to find any published reports of plant CPR activity under VA stress. The highest CPR activity of 10.47 mmol min\({}^{-1}\) reported at OTC 50 mg kg\({}^{-1}\) in pepper and the lowest (1.69 mmol min\({}^{-1}\)) at SDZ 10 mg kg\({}^{-1}\) in carrot. The response of the CPR varied depending on the plant species, the plant tissue analyzed, and the intensity of stress (VAs concentration).  
With increasing concentrations of SDZ and OTC in the soil-manure mixture, a gradual increase in GST activity was observed (Figure 3). A previous study showed a significant increase in GST activity of pinto beans grown un chlortetracycline treated soil [11]. GSTs are known to safeguard the cells against chemical-induced toxicity and provide tolerance [29]. In plants, GSTs reportedly provide tolerance to herbicides [30]. In carrot, the overall GST activity for SDZ and OTC was lower, in comparison with control, enforcing the inhibitory effect of SDZ and OTC on GST activity. Alternately in lettuce, low doses (10 mg kg\({}^{-1}\)) resulted in significant inhibition of GST activity. On the contrary, in comparison with control, no significant difference (\(p<0.05\)) in GST activity was observed with STR treatment.  
Therefore, under VA stress, there was an onset of the plant detoxification system, which varied depending upon the type of VAs and plant species.  
Figure 2: NADPH-cytochrome P450 reductase activity of lettuce, carrot, and pepper grown in soil treated with VAs. Error bars represent standard error. Concentration values followed by different letters are significantly different (\(p<0.05\)) according to [PERSON]’s multiple range test. SDZ = Sulfadimethoroxine; OTC = Oxytetracycline; STR = Streptomycin.