蚕豆叶片发育与衰老过程中超氧物歧化酶活性与丙二醛含量变化

Changes of SOD Activity and MDA content During Development and Senescence of Broad Bean Leaves

蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2^+产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2^+代谢中间产物累积而引起膜的损伤.

The superoxide dismutase (SOD) is present in all aerobic cells and plays an essential role in allowing organisms to survive in the presence of O_2. The surperoxide radical anion O_2^- is regarded as the primary agent of oxygen toxicity. It has been proven that leaf senescence in vitro is Partly due to the decrease of SOD activity and lipid peroxidation. However,the change of SOD isoenzyme and its subcellar localization in situ had not been reported. In this paper, the su- bcellar localization of SOD and the changes of its isoenzyme in broad bean (Vicia faba L.) leaves during development and senescence were studied. The purpose of this study is to explore the relationship between the rate of O_2^- produc- tion and the system of enzymatic O_2^- removal during leaf senescence. The degree of development and senescence of broad bean leaves depends obviously on their position on the stem. The decrease of chloro- phyll and protein content could be used as a criterion of senescence. Different pellets were obtained by differential centrifugation from leaf tissue homogenate. Activity of SOD was assayed by nitroblue tetrazolium(NBT) at pH 7.8. Most of the SOD acivity was in the chloroplast and supernatant (soluble fraction), and only a little (3～5%) in mitochondria. It was shown that total activity of SOD and its relative activity in chloroplasts decreased in senescent leaves. Electrophoresis of various SOD fractions was carried out in gels of 7.5% acrylamide. Three bands of SOD isoenzymes were found in leaf extracts and their R_f values were 0.25, 0.84 and 0.88 respectively. Two bands with R_f 0.25 and 0.88 were found in chloroplasts, and two bands with R_f 0.84 and 0.88 in mitochondria. The bands of R_f 0.25 and 0.84 declined with the senescence of the 1eaves. The rate of O_2^- prodution increased slightly with the advance of leaf age, but the content of MDA increased repidly before the leavcs began to turn yellow and withered. The increase of MDA produced by lipid peroxida- tion reflected the accumulation of superoxide radical toxicity. Catalase activity decreased more rapidly than that of SOD during the senescence of leavcs. The disparity between SOD activity and catalase activity during leaf senescence might result in the formation of O_2^- intermediates, such as H_2O_2 and OH, which cause the damage of the mambrane.