黄皮种子线粒体呼吸速率和活性氧清除酶活性对脱水的响应及其生态学意义

顽拗性种子脱落时具有较高的含水量和代谢活性, 对脱水高度敏感; 但顽拗性种子脱水敏感性的机理至今仍然不清楚。该文以顽拗性黄皮(Clausena lansium)种子为材料, 研究了种子和胚轴对水分丧失的响应, 在脱水过程中胚轴和子叶的呼吸速率, 胚轴和子叶线粒体的细胞色素c氧化酶(CCO)活性、外膜完整性、CCO和交替氧化酶(AOX)途径以及线粒体活性氧清除酶活性的变化。结果表明, 随着水分的丧失, 种子和胚轴的存活率逐渐下降, 种子的脱水敏感性大于胚轴; 胚轴和子叶的呼吸速率以及线粒体外膜的完整性降低。胚轴和子叶线粒体的CCO途径以及胚轴AOX途径的呼吸速率在脱水初期增加, 随着继续脱水下降, 胚轴线粒体AOX途径的呼吸速率则随着脱水显著下降。胚轴线粒体的超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)和谷胱甘肽还原酶(GR)活性和子叶线粒体的APX活性随着脱水迅速下降; 胚轴线粒体的脱氢抗坏血酸还原酶(DHAR)活性和子叶线粒体的SOD、DHAR和GR活性在脱水初期增加, 然后下降。这些数据表明黄皮种子的脱水敏感性与线粒体的呼吸速率和活性氧清除酶的活性降低密切相关, 也与长期适应热带/亚热带的生境有关。

Response of respiratory rate and reactive oxygen species scavenging enzyme activity in seed mitochondria of Clausena lansium dehydration and its ecological significance

Aims Recalcitrant seeds shed at relatively high water contents and metabolism activities are sensitive to dehydration. However, the mechanism for desiccation sensitivity of recalcitrant seeds is unclear. Here, we used the recalcitrant Chinese wampee (Clausena lansium) seeds as materials to investigate the relationship between desiccation sensitivity and the change in respiratory rate and reactive oxygen species (ROS) scavenging enzyme activity of mitochondria. Methods We dehydrated Chinese wampee seeds at 25–28 °C and 72%–80% relative humidity for 0, 4, 7 and 10 days then assayed the survival of seeds and axes, changes in respiratory rate of axes and cotyledons, activity of cytochrome c oxidase (CCO), integrity of outer mitochondrial membrane, pathways of CCO and alternative oxidase (AOX) and activities of ROS scavenging enzymes in mitochondria of axis and cotyledon. Important findings With the loss of water content, survival of seeds and axes gradually decreased, and desiccation sensitivity of seeds was greater than that of axes. Respiratory rate and integrity of outer mitochondrial membrane of axes and cotyledons decreased with dehydration. Respiratory rate of CCO pathway in mitochondria of axis and cotyledon and of AOX pathway in mitochondria of cotyledon increased in the initial phase of dehydration and then decreased, and that of AOX pathway in mitochondria of axis significantly decreased with dehydration. Activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) in axis mitochondria and those of APX in cotyledon mitochondria decreased with dehydration, and those of dehydroascorbate reductase (DHAR) in axis mitochondria and of SOD, DHAR and GR in cotyledon mitochondria increased in the initial phase and then decreased. Our data indicate that desiccation sensitivity of Chinese wampee seeds is closely related to decreases in respiratory rate and reactive oxygen species (ROS) scavenging enzyme activity of mitochondria and also to long-term adaptation to the tropical/subtropical habitat.