Grass pea(Lathyrus sativus L.) seedlings cultured in hydroponic solution for 7 days were used as experimental materials.Different concentrations of H₂O₂ were applied to hydroponic solution for 24 h to stress L.sativus seedlings.In order to reveal the tolerance mechanisms of oxidative stress in L.sativus roots,the extent of oxidative stress and the response of antioxidant system to oxidative stress were analyzed in roots.Results showed that:(1)The weight of fresh roots reduced significantly.However there was no significant change in the number of lateral roots with H₂O₂ concentration increasing.(2)The scope and extent of H₂O₂ staining was significantly increased,but the apical region always remained relatively low levels of H₂O₂.In contrast,the scope and extent of O^-·₂ staining were significantly reduced and the apical region always maintained a high level of O^-·₂.(3)The content of ascorbic acid(ASC) and the activities of catalase(CAT),peroxidase(POD) and ascorbate peroxidase(APX) all exhibited a decrease trend after an initial increase.However,superoxide dismutase(SOD) has been showing an upward trend.The results above showed that O^-·₂ accumulation could be positively related to the growth and vigor of L.sativus root and H₂O₂ accumulation could be positively related to the extent of oxidative stress.The studies also confirmed that low concentrations of H₂O₂ treatment could improve the scavenging ability of antioxidant system for ROS in L.sativus roots.