| The herbicide isoproturon is wildly used for controlling of weed/grass in wheat arable lands. However, the side effect of isoproturon as contaminants on crops is unknown. In this study, we investigated isoproturon-induced oxidative stress in wheat (Triticum aestivum).The dosage-toxicity effect of isoproturon on inhibition of germination rates, bud and root elongation of two wheat cultivars (T. aestivum, cv. Ning 13 and T. aestivum, cv. Ning 9) was studied in this paper by indoor training. Results indicate that the isoproturon exposure had minor effects on both seed germination and early seedling growth at a relatively low dose (0-40μg/ml) . NM-13 showed a higher sensitivity to isoproturon than NM-9.Effects of different concentrations isoproturon on growth, oxidative stress, and antioxidant response of wheat seedlings (T. aestivum, cv. Ning 13) were investigated using pot experiments. Wheat plants were cultured in soils with isoproturon at 0-20 mg/kg and showed negative biological responses. Results obtained from this study show that the tested herbicide slightly affected the wheat growth at a relatively low dose but exerted a remarkable effect at high level. Treatment with 10 and 20 mg/kg isoproturon decreased the root length to 68% and 43.4 % of the control, respectively. The similar inhibition of shoot elongation was observed with a 21.8% and 32.8% decrease as compared to the control, respectively. Chlorophyll content significantly decreased at the low concentration of isoproturon (2 mg/kg), suggesting that chlorophyll was rather sensitive to isoproturon exposure and isoproturon as phenylurea herbicide might be active in the chloroplast electron-transport system and disturb the photosynthesis of its target plants. Exposure of wheat plants to isoproturon led to lipid peroxidation in leaves. The level of lipid peroxides, expressed as thiobarbituric acid reactive substances (TBARS), was elevated with the isoproturon applied. The wheat leaves showed a greater response to the isoproturon exposure maybe because they accumulated more peroxidation products. The great accumulation of TBARS observed in leaves at 10 mg/kg isoproturon are 1 fold higher than the control. However, a further increase in isoproturon concentration to 20 mg/kg failed to promote the accumulation of TBARS. The exposure of isoproturon could not result ingreatly enhanced TBARS content in roots of wheat. The contents of protein and proline were also elevated with the increasing isoproturon.To deal with the isoproturon-induced oxidative stress, wheat plants activated a variety of antioxidative enzymes, like SOD, CAT APX and POD to diminish the reactive oxygen species. Additionally, the activity of GST, one of typical detoxifying enzymes was elevated in response to isoproturon. Activities of the antioxidant enzymes showed a general increase at low isoproturon concentrations (2-10 mg/kg) and decrease at high isoproturon concentration (20 mg/kg). Activities of CAT in leaves showed progressive suppression under the isoproturon exposure.To get an insight into the effect of isoproturon on the enzymes, a non-denaturing polyacrylamide gel electrophoresis (PAGE) for SOD, POD and CAT activities was performed. Under the conditions of this study, only two isoforms of SOD were detected. The patterns of these isoforms were similar in response to isoproturon exposure. At least four bands of POD isoforms in the wheat root were detected. All isoforms of POD in roots showed increasing activities at 3.5-10 mg/kg of isoproturon. Six bands were detected in leaves. However, with regard to isoforms I, II, III and IV, no difference of the activities between the treatments and control was observed. For isoform VI, only a slight increase in activity of POD was found relative to the control. We also performed native PAGE for catalase. Only one isoenzyme of CAT in the wheat was detected. The above results indicate the involvement of all of these enzymes in the similar response to the herbicide. |
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