中文摘要：

目的：研究百草枯诱导的氧化胁迫在涡虫严重致死率发生中的角色。方法：动物的存活率用于反映涡虫的致死率。百草枯用来诱导严重的氧化胁迫,氧化胁迫的发生程度通过过氧化物酶（SOD）的活性变化来监测。游离氧自由基清除剂DMSO用来在百草枯处理前或后处理涡虫。结果：浓度为2 mmol.L-1百草枯处理1 h显著降低SOD活性,而2 mmol.L-1百草枯处理2、4、8 h可以导致更严重的SOD活性降低。暴露2 h后,浓度为1 mmol.L-1百草枯不明显影响SOD活性,而浓度为2、3与4 mmol.L-1的百草枯处理则显著降低SOD活性。同时,经浓度为2、3与4 mmol.L-1百草枯处理后,继续发育3 d的涡虫存活率发生了显著的降低。进而,对浓度为2 mmol.L-1百草枯处理2、4与8 h涡虫进行预先或延后DMSO（0.1%）处理4 h可以显著增加百草枯处理动物的SOD活性。尽管如此,在2 mmol.L-1百草枯处理2、4与8 h基础上再进行DMSO（0.1%）预先或延后处理4 h涡虫动物的SOD活性尚不能够达到正常涡虫中的SOD活性水平。而且,对浓度为2 mmo.lL-1百草枯处理2、4与8 h涡虫进行预先或延后DMSO（0.1%）处理4 h还可以显著提高百草枯处理动物的存活率。结论：DMSO预先或延后处理可以有效地预防或恢复百草枯暴露涡虫中经氧化胁迫诱导的严重致死率毒害。

英文摘要：

Objective：To investigate the roles of oxidative stress induced by paraquat treatment in the formation of severe of lethality in planarian Dugesia japonica.Methods：The percentage of survival animals was used to reflect the lethality.The paraquat was used to induce the formation of severe oxidative stress,which was monitored by the superoxide dismutase（SOD） activity.DMSO,an effective free radical scavenger,was used to treat the planarians before or after the paraquat treatment.Results：The significant decrease of SOD activity was observed in planarians exposed to 2 mmol·L-1 of paraquat for 1 h,and more severe decreases of SOD activity were further detected in planarians exposed to 2 mmol·L-1 of paraquat for 2,4,and 8 h.After 2 h exposure,1 mmol·L-1 of paraquat treatment did not induce an obvious alteration of SOD activity;however,the significant decreases of SOD activities were observed in paraquat exposed planarians at the concentrations from 2 mmol·L-1 to 4 mmol·L-1.Moreover,three days after the paraquat treatment,the significant decreases of percentages of survival animals were observed in planarians exposed to 2,3,and 4 mmol·L-1 of paraquat.Furthermore,the significant increases of SOD activities were detected in 2 mmol·L-1 paraquat exposed planarians for 2,4,and 8 h pre-or post-treated with 0.1% DMSO for 4h compared with those in 2 mmol·L-1 paraquat exposed planarians for 2,4,and 8h,respectively.Nevertheless,the values of SOD activities in 2 mmol·L-1 paraquat exposed planarians for 2,4,and 8 h pre-or post-treated with 0.1% DMSO for 4h could not reach the value of SOD activity in planarians without paraquat treatment.The significant increase of percentage of survival animals was further observed in 2 mmol·L-1 paraquat exposed planarians for 2 h pre-or post-treated with 0.1% DMSO for 4 h compared with that in 2 mmol·L-1 paraquat exposed planarians for 2 h.Conclusion：These data suggest that pre-or post-treatment with DMSO can effectively prevent or retrieve the formation of oxidative stress-i