中文摘要：

通过盆栽试验研究了土壤外源Cd污染胁迫对小麦幼苗生长、Cd吸收、自由基代谢及抗氧化酶活性的影响。结果表明，土壤Cd含量在0～33mg·kg^-1。范围内，小麦未产生明显的毒害症状，且Cd含量低于3．3mg·kg^-1时促进小麦生长；随着土壤外源Cd浓度的增加，小麦根系和叶片Cd含量显著增加。电子顺磁共振（EPR）研究结果显示，小麦叶片自由基水平高于根系，且随Cd浓度的变化，叶片自由基响应比根系更敏感；与对照相比，Cd浓度低于3．3mg·kg^-1时，Cd处理使小麦叶片自由基水平降低．高浓度的Cd处理（≥3．3mg·kg^-1），则使小麦叶片自由基水平升高。叶片SOD、CAT、POD、APX等抗氧化酶在低于3．3mg·kg^-1的Cd处理时．没有明显变化，但更高浓度的Cd处理则诱导酶活性升高，表明氧化胁迫程度增加。综合生物量、自由基变化及抗氧化酶的响应结果．初步确定土壤外源Cd对小麦幼苗的毒性临界点在3．3～10mg·kg^-1之间。

英文摘要：

Effects of soil Cd concentration （0-33 mg· kg^-1） on growth, Cd accumulation, free radical metabolism and antioxidant system of wheat seedlings （Triticum aestivum L.） were investigated by using pot experiments in this study. No obvious toxic symptom in seedlings was observed in the whole dose range. However, a slightly positive effect on the seedling growth was observed at low Cd concentrations （less than 3.3 mg· kg^-1）. EPR investigation showed that the level of free radicals in the leaves was higher than that in the roots, and responded sensitively to soil Cd exposure. When exposed to lower Cd （less than 3.3 mg· kg^-1）, the level of free radicals in the leaves decreased, but significantly in- creased with increasing Cd concentrations. The activities of some antioxidant enzymes in the leaves, including superoxide dismutase （SOD, EC 1.12.1.1）, catalase （CAT, EC 1.11.1.6）, gnaiacol peroxidase （POD, EC 1.11.1.7）, ascorbate peroxidase （APX, EC 1.11.1.11）, did not change much at low Cd concentrations （less than 3.3 mg· kg^-1）, but fluctuated drastically at high Cd concentrations. Based on the results of this study, we propose that the toxic critical value of soil Cd in inducing oxidative stress to wheat seedlings is between 3.3 mg·kg^-1 and 10 mg· kg-1.