Effects Of Herbicide Fluroxypyr On Biological Toxicology Of Rice Seedlings Plants

Fluroxypyr, as a common agricultural herbicide is widely used for controlling annual or perennial weeds. However, its substantial use in conventional agricultural practices has resulted in continuous and biological toxicity. In this study, we investigated fluroxypyr-induced toxicity in rice.1. Effects of fluroxypyr on germination of rice seedsThe germination, bud and root of rice seeds (Oryza sativa L. cv. Xu 3) showed negative correlation with fluroxypyr at 0～0.8 mg L-1. The elongation of root showed more sensitive than that of bud for fluroxypyr. The inhibition rate of rice seed germination treated with 0.2 and 0.8 mg L-1 fluroxypyr were 23.5% and 42.4%, respectively. The inhibition rate of root and bud elongation treated with 0.8 mg L-1 fluroxypyr were 85.1% and 49.4%, respectively.2. Effects of fluroxypyr on growth and antioxidant of rice seedlingsAfter rice seeds germination, rice seedings were cultured in polyvinylchloride pots contained with 1/2-strength nutrient solution (IRRI). After growing for fourteenth day stage rice plants were cultured in the nutrient solution containing with fluroxypyr at 0～0.8 mg L-1 for 6 days. The fresh weight, dry weight and chlorophyll content of rice seedings showed negative biological responses with fluroxypyr treatmeat. There were significant differences in shoot elongation between control and treatment with fluroxypyr. To valuate fluroxypyr-induced toxicity in rice, the oxidative damage to cells was examined by measuring the content of malondialdehyde (MDA), an indicator of lipid peroxidation. Exposure of rice to fluroxypyr at increasing levels led to lipid peroxidation in both roots and leaves. The maximum accumulation in roots was observed at 0.2 mg L-1 of fluroxypyr, in which increased the contents of MDA to 43.3%. The maximum accumulation in leaves was observed at 0.4 mg L-1 of fluroxypyr, which increased the contents of MDA to 22.5%. However, a further increase in fluroxypyr concentration failed to promote the accumulation of MDA. In this study, using histochemical staining with nitroblue tetrazolium and 3,3-diaminobenzidine we observed the increased levels of accumulation O2- and H2O2 in the plant of rice leaves exposed to fluroxypyr resulted in the peroxidation of plasma membrane lipids. Treatment with 0.8 mg L-1 fluroxypyr increased 52.6% production rate of superoxide radical accumulation in rice roots. Treatment with fluroxypyr increased proline accumulation in plants, being expressed the most at 0.8 mg L-1. Activities of EST in rice seedings plant showed a similar pattern with proline. The top activity was observed at 0.8 mg L-1, where the activities of EST from leaves and roots increased by 1.96- and 1.47-folds, respectively.3. Fluroxypyr-induced oxidative stress in rice seedlingsActivities of the antioxidant enzymes (SOD, CAT, POD, APX, GSTs and GR) showed a general increase at low concentrations of fluroxypyr and a decrease at high levels of fluroxypyr (except for POD and GSTs). Activities of CAT and APX in leaves and roots showed high activities at 0.1 mg L-1 of fluroxypyr. High Activities of SOD and GR in leaves and roots were observed at 0.2 mg L-1 of fluroxypyr. Activities of POD in leaves and roots showed high activities at 0.8 mg L-1 of fluroxypyr. Significantly positive correlation was observed between GSTs and fluroxypyr levels in rice leaves. GSTs activity in roots was significantly reduced by fluroxypyr teatment. Moreover, GSTs activity in roots was dramatically higher than that in leaves. This suggested that the possibility of organ-specific GSTs expression and functions could not be ruled out. The antioxidant enzymes activities in rice seedings treated with fluroxypyr were comfirmed by the results of non-denaturing polyacrylamide gel electrophoresis (PAGE) for SOD, POD and CAT.