Effects of cadmium on reactive oxygen species metabolism, activities and gene expressions of superoxide dismutase and catalase in maize （zea mays） seedling

صينى. 【目的】研究镉胁迫对玉米（Zea Mays）幼苗活性氧代谢，超氧化物歧化酶（SOD）和过氧化氢酶（CAT）的活性及其基因表达的影响。【方法】用营养液培养的方法研究了不同镉浓度（0、5、20和100μmol・L. 1）和处理时间（12、24、48、96和168 h）下玉米幼苗内活性氧代谢、SOD和CAT活性及其基因表达的变化。【结果】镉处理后植株内超氧自由基（O2. _）产生速率迅速升高，24 h（叶）或48 h（根）后又逐步下降；H2O2随镉浓度和处理时间的增加而大量积累。镉处理的植物SOD活性开始随镉浓度升高，48 h后被消耗和抑制逐步下降，但后期100μmol・L. 1镉处理的活性仍显著高于其它处理；CAT活性除叶中100μmol・L. 1镉处理被抑制降低外均被诱导,开始随镉浓度升高，随后随镉浓度和胁迫时间逐步下降。镉诱导的SOD基因表达与其活性变化相似，而CAT基因表达随镉浓度和处理时间逐步增强，说明在玉米幼苗内镉通过抑制SOD的基因转录抑制其活性，而对CAT，镉胁迫导致其产生了翻译后蛋白修饰。【结论】镉处理诱导了玉米幼苗内活性氧产生、SOD和CAT的活性及基因表达增加，随胁迫的加剧，SOD和CAT的活性和SOD表达被抑制，CAT则产生转录后或翻译后修饰。

إنجليزي. [Objective] The aim of this experiment was to examine the effects of cadmium stress on the metabolism of reactive oxygen species （ROS）, the activities and the gene expressions of superoxide dismutase （SOD） and catalase （CAT） in maize （Zea Mays） plants. [Method] Maize seedlings were treated with 0, 5, 20 and 100 μmol・L. 1 Cd for periods of 12 to 168 h under hydroponic condition. [Result] The results showed that the generation rate of superoxide radical （O2. _） was increased at first with Cd stress, then decreased in leaves and roots after 24 h and 48 h Cd exposure respectively. The levels of hydrogen peroxide （H2O2） rose with the increasing cadmium concentration and the prolonged Cd exposure time. SOD activities in plants were enhanced by 12 h and 24 h Cd exposure. Moreover, higher SOD activities in leaves and roots were observed under higher Cd concentrations. The expressions of genes encoding SOD showed the same trends as SOD activities in plants exposed to Cd, indicating that Cd affected SOD function in gene transcription level in maize plants. CAT activities in plants were increased with 5-20 μmol・L. 1 Cd treatments, but decreased under 100 μmol・L. 1 Cd exposure. CAT gene expressions in leaves increased with Cd concentration and exposure time,suggesting that Cd caused post-translation modification of CAT protein. [Conclusion] The ROS generation in maize seedlings was induced by Cd stress, which might result in the changes of antioxidant enzymes such as SOD and CAT in their activities and corresponding gene expressions.