Physiological Responses Of Wheat Seedlings To Omethoate And 1, 2, 4-trichlorobenzene Stress

[Objectives] Wheat seedlings(Triticum aestivum L. cv. Xindong No.17) was grown hydioponically to investigate the effect of varing concentrations of omethoate and 1,2,4-trichlorobenzene on growth parameters, photohysynthetic and physiological characteristics, cell membrane stability, antioxidative enzymes and non-enzymatic antioxidants, lipid peroxidiation and cell death, osmotic compunds, and omethoate content. We attempt to obtain more detailed information on wheat responses to omethoate and 1, 2,4-trichlorobenzene stress to minimize the negative effects of organic contaminants on crop production, food safety and eco-environments.[Methods] Wheat (Triticum aestivum L. cv. Xindong No.17) was grown hydioponically to investigate physiological responses under different stresses of omethoate (0,0.1,1.0,5.0 and 10.0 g/L) or 1,2, 4-trichlorobenzene treatments (0,10,20,40 and 80 mg/L) in a climate chamber. The Hoagland nutrient solutions were renewed every 5 days and aerated 8 hours daily. The uniform-sized seedlings were transplanted into half-strength Hoagland nutrient solution for 3 days, and grown for further 10 days in full-strength Hoagland nutrient solution. Plant samples were collected at 1,3,5 and 7 days after omethoate treatment and 7 days after 1,2,4-trichlorobenzene treatment, respectively, and stored in a freezer at -70℃for assay of physiological parameters.[Results] 1) The fresh weight and protein content of wheat seedlings were decreased with addition of omethoate and 1,2,4-thrichlorobenzene throughout the whole experimental duration, and were dose-dependent. There was significant difference in fresh weght and protein content between the extremely low concentrations of 1,2,4-thrichlorobenzene and control.2) The chlorophyll content and carotenoid content in leaves of wheat seedlings were suppressed with addition of omethoate and 1,2,4-thrichlorobenzene throughout the whole experimental duration, and were dose-dependent. The chlorophyll content and carotenoid content in leaves of wheat under omethoate stress was also time-dependent. Besides, there was significant difference in content of chlorophyll and carotenoid between the extremely low concentrations of 1,2,4-thrichlorobenzene and control.3) The content of MDA and soluble sugar in leaves of wheat seedlings were raised with increaseing rate of omethoate and 1,2,4-trichlorobenze. In addition, the proline content in leaves of wheat seedlings was also raised with omethoate concentration and exposure time. Besides, the electrolytic leakage and lipid peroxidatipon (cell death) indicated by Evans blue staining were enhanced with increasing concentrations of 1,2,4-trichlorobenze, compared with the control.4) Under omethoate stress, the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) in leaves and roots of wheat seedling were promoted at low omethoate concentrations and then suppressed at high omethoate concentrations, as compared with the control. The maximal value of SOD, POD, APX and GR activities in leaves of wheat seedlings was observed in 5.0 g/L omethoate treatment but the maximal value of SOD, POD and CAT activities in roots was observed in 1.0 g/L omethoate treatment. In addition, under 1,2,4-trichlorobeneze stress, the activities of SOD, POD, CAT, APX and GR in leaves were enhanced with increasing exposure level of TCB and the maximal value of SOD, POD, CAT, APX and GR activities in leavies of wheat seedlings was observed in 80 mg/L 1,2,4-thrichlorobenzene treatment. Besides, the activities of SOD, POD, CAT, APX and GR in roots were promoted at low TCB concentrations but were suppressed at higher exposure levels of TCB in comparison with the control. The maximal value of SOD, POD, CAT, APX and GR activities in roots was observed in 20 mg/L 1,2,4-trichlorobeneze treatment. Morever, rate of production of O2 in root was raised at low TCB concentration treatments but was decreased at high TCB concentration treatments, respectively, compared with the control. No significant difference was observed in leaves between any two of the TCB treatments.5) The AsA content in roots and GSH content in wheat seedlings were promoted with increasing levels of TCB and dose-dependent. In contrast, the AsA content in leaves was decreased with addition of TCB concentration.6) Omethoate content of wheat seedlings was raised with increasing concentrations of omethoate and with exposure time. But the accumulation rates of omethoate in leaves were decreased with exposure time.7) Wheat seedlings were more sensitive to 1,2,4-thrichlorobenzene stress than to omethoate stress. Besides, the growth and physiological of wheat seedlings was significantly inhibited by 10 mg/L 1,2, 4-thrichlorobenzene treatment, and roots were more severely damaged than leaves under omethoate and 1, 2,4-trichlorobenze stress.8) Wheat seedlings under omethoate and 1,2,4-trichlorobenze stress were damaged through oxidative stress and lipid peroxidation caused by excess accumulation of ROS in plant.[Conclusion] As a result, the growth and physiological activity of wheat seedlings were significantly inhibited under omethoate and 1,2,4-trichlorobenze stress. No significant inhibition was observed in wheat seedlings grwon under low omethoate concentrations, but significant damage occurred in wheat seedlings grown under low 1,2,4-trichlorobenze concentrations. Moreover, different physiological mechanisms were found in wheat roots and shoots in response to omethoate and 1,2,4-trichlorobenze.