Cold acclimation-dependent physiological changes were investigated through photosynthetic activity and some antioxidant enzymes in two winter oilseed rape cultivars ( Brassica napus L. ssp. oleifera cvs. Eurol and Hansen) on the basis of leaf age. Chlorophyll fluorescence measurements demonstrated that cold acclimation caused decreased photosynthetic activity in Eurol and Hansen as the leaf age increased. Photosynthetic pigment content declined in both cultivars under low temperature irrespective of leaf age. In Eurol, however, relatively higher total carotenoid content than Hansen may provide a protection against photooxidative damage. Superoxide dismutase, ascorbate peroxidase and glutathione reductase activity in the cold-acclimated leaves of Hansen significantly increased, indicating an effective ascorbate–glutathione cycle activity. In Eurol, however, ascorbate peroxidase and glutathione reductase activity in the cold-acclimated younger leaves lowered and hydrogen peroxide detoxifying system collapsed. As a result, decreased photosynthetic activity in the young leaves of Hansen under low temperature could be manifested as a metabolic response that downregulate photosynthesis to attain cold-acclimated state. In the case of Eurol, cold acclimation process caused oxidative stress. In summary, the changes in the chlorophyll fluorescence parameters in the young leaves of Hansen are derived from some metabolic regulation as a result of cold acclimation, whereas in Eurol, it is due to oxidative stress triggered by low temperature. Leaf maturation mitigated the adverse effects of low temperature in the leaves of Eurol and Hansen.

中文翻译：

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冷驯化条件下叶龄对冬油菜叶片叶绿素荧光和抗氧化酶活性的影响

在叶龄的基础上，通过光合活性和一些抗氧化酶研究了两个冬季油菜品种（欧洲油菜 ssp. oleifera cvs. Eurol 和 Hansen）的冷驯化依赖性生理变化。叶绿素荧光测量表明，随着叶龄的增加，冷驯化导致 Eurol 和 Hansen 的光合活性降低。无论叶龄如何，低温下两个品种的光合色素含量均下降。然而，在 Eurol 中，与 Hansen 相比，总类胡萝卜素含量相对较高，可以提供对光氧化损伤的保护。汉森冷驯化叶片中超氧化物歧化酶、抗坏血酸过氧化物酶和谷胱甘肽还原酶活性显着增加，表明抗坏血酸-谷胱甘肽循环活性有效。在欧罗，然而，冷驯化的嫩叶中的抗坏血酸过氧化物酶和谷胱甘肽还原酶活性降低，过氧化氢解毒系统崩溃。因此，低温下汉森幼叶光合活性降低可能表现为一种代谢反应，下调光合作用以达到冷驯化状态。在 Eurol 的情况下，冷驯化过程引起氧化应激。综上所述，汉森幼叶中叶绿素荧光参数的变化源于冷驯化导致的某些代谢调节，而在Eurol中，则是由于低温引发的氧化应激。叶子成熟减轻了低温对 Eurol 和 Hansen 叶子的不利影响。冷驯化嫩叶中的抗坏血酸过氧化物酶和谷胱甘肽还原酶活性降低，过氧化氢解毒系统崩溃。因此，低温下汉森幼叶光合活性降低可能表现为一种代谢反应，下调光合作用以达到冷驯化状态。在 Eurol 的情况下，冷驯化过程引起氧化应激。综上所述，汉森幼叶中叶绿素荧光参数的变化源于冷驯化导致的某些代谢调节，而在Eurol中，则是由于低温引发的氧化应激。叶成熟减轻了低温对 Eurol 和 Hansen 叶片的不利影响。冷驯化嫩叶中的抗坏血酸过氧化物酶和谷胱甘肽还原酶活性降低，过氧化氢解毒系统崩溃。因此，低温下汉森幼叶光合活性降低可能表现为一种代谢反应，下调光合作用以达到冷驯化状态。在 Eurol 的情况下，冷驯化过程引起氧化应激。综上所述，汉森幼叶中叶绿素荧光参数的变化源于冷驯化导致的某些代谢调节，而在Eurol中，则是由于低温引发的氧化应激。叶成熟减轻了低温对 Eurol 和 Hansen 叶片的不利影响。