不同浓度镉胁迫对玉米幼苗光合作用、脂质过氧化和抗氧化酶活性的影响

以玉米为材料，通过营养液培养试验，研究浓度为5~100 μmol/L的镉胁迫后不同时间内，植株体内活性氧代谢及其抗氧化酶活性的变化特征，探讨镉胁迫导致植物体内活性氧自由基累积的原因及不同程度镉胁迫对植物体内活性氧代谢的影响。随着加镉量的增加，玉米地上部生物量明显降低，而根部生物量未表现出差异。镉处理降低了叶片光合作用速率，高镉处理的影响较早。镉处理4d后，5、20、和100 mol/L Cd2+浓度处理玉米叶片Fv/Fm减小，PSII系统的原初光能转换效率下降，但比光合作用速率下降的时间要晚；镉处理7d的叶片中丙二醛（MDA）含量还没有受到明显影响，但20和100 μmol/L Cd2+处理4d后，根系膜质过氧化增强，MDA含量升高。随着镉浓度升高，处理时间延长，活性氧酶清除系统包括超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）和谷胱甘肽还原酶（GR）等酶活性明显增加，受到镉胁迫诱导，高浓度镉处理该现象出现更早。本文试验结果表明，镉胁迫下植物体内活性氧形成增多，诱导活性氧酶清除系统活性升高，其中一个重要原因是与CO2同化受到限制有关。

Effect of cadmium stress on photosynthesis, lipid peroxidation and antioxidant enzyme activities in maize (Zea mays L. ) seedlings

To gain better insight into the biological mechanisms of reactive oxygen species in cadmium-stressed plants, hydroponics culture experiment was conducted to examine the effects of cadmium stress on photosynthesis, lipid peroxidation and antioxidant enzyme activities in maize plants. Maize seedlings were treated with 5, 20, and 100 µmol/L Cd²⁺ for periods of 12 to 168 h. One week of Cd addition decreased shoot biomass, but did not affect root dry matter weight yet. The photosynthesis rate in leaves began to be inhibited by 24 h exposure to 100 µmol/L Cd²⁺ and decreased with increasing Cd concentrations and prolonged Cd treatment. The reduction of potential maximal quantum yield of PSII due to Cd stress occurred later than that of photosynthesis rate. After 96 h treatments of 20 and100 μmol/L Cd²⁺, the levels of malondialdehyde (MDA) in roots increased, but MDA concentrations in leaves did not increase even after 7 days of Cd treatment. The activities of antioxidant enzymes such as superoxide dismutase (SOD, EC1.15.1.1), ascorbate peroxidase (AsA-POD, EC1.11.1.11), guaiacol peroxidase (EC1.11.1.11), catalase (CAT, EC 1.11.1.6) and glutathione reductase (GR, EC1.6.4.2) in leaves and roots increased first by Cd treatments, then declined or did not change. This trend was more obvious with higher concentrations of Cd and extended Cd treatment. Cd had little effect on dehydroascorate reductase (DHAR, EC1.8.5.1) activities in leaves and roots during periods of 12-168 h. Early inhibition of CO₂ assimilation by Cd stress was suggested to result in increased production of reactive oxygen species in maize seedlings, which would induce the increased activities of some antioxidant enzymes.