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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。
Recalcitrant seeds have higher water content and metabolic activity when they fall off, and are highly sensitive to dehydration. However, the mechanism of recalcitrant seeds dehydration sensitivity remains unclear. In this paper, we studied the response of seeds and hypocotyls to water loss by using Clausena lansium seeds. During the dehydration process, the hypocotyls and cotyledons’ respiratory rate, mitochondrial cytochrome c oxidation in the hypocotyls and cotyledons (CCO) activity, outer membrane integrity, CCO and AOX pathways, and mitochondrial ROS scavenging enzyme activity. The results showed that with the loss of water, the survival rate of seeds and hypocotyl decreased gradually, and the dehydration sensitivity of seeds was greater than that of hypocotyl; the hypocotyl and cotyledon respiration rate and the integrity of mitochondrial outer membrane decreased. The CCO pathway of hypocotyl and cotyledon mitochondria and the respiration rate of hypocotyl AOX pathway increased at the initial stage of dehydration, and the respiration rate of hypocotyl AOX pathway decreased significantly with dehydration as desiccation continued to decrease. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) in mitochondria of hypocotyls and APX activities in mitochondria of cotyledons decreased rapidly with dehydration. The dehydrogenation of hypocotyls Ascorbate reductase (DHAR) activity and cotyledon mitochondrial SOD, DHAR and GR activities increased early in dehydration and then decreased. These data suggest that the dehydration sensitivity of yellow seed is closely related to the decrease of mitochondrial respiration rate and activity of ROS scavengers and to the long-term adaptation to tropical / subtropical habitats.