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Mechanism for Relaxation of Photooxidative Stress in Plants.

植物光氧化应激的缓解机制。

基本信息

批准号：
05044130
负责人：
ASADA Kozi
金额：
$ 3.84万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

项目摘要

Under environmental conditions where plants are exposed to a bright sunlight that cannot be utilized, excess photons generate active oxygens, which cause photooxidative damages to plants. For the protection from such damages, plants have the following two relaxation systems.1. Suppression of the production of active oxygensCyclic electron flow suppresses the production of active oxygens through the down-requlation of photosystem II,but, the mediator between the photoreductants (either ferredoxin or NADPH) had not been identified. In the cyanobacterium Synechocystis 6803, a NADPH-specific pyridine nucleotide dehydrogenase (NDH) mediates an electron transfer from NADPH to the thylakoid-plasto-quinone (PQ), which was established by analysis of chlorophyll fluorescence and redox reaction of P700 using the NDH-less mutant cells. Further, in maize thylakoids, LED-array spectrophotometer allows to detect a cytochrome b-559 with a low redox potential and its participatation in the ferredoxin-mediated cyclic electron flow around photosystem I.Kinetic analysis of O_2^--production in thylakoids indicates also the O_2^--mediated cyclic electron flow around photosystem I.2.Scavenging of active oxygens in chloroplastsMicrocomparteantalization of the scavenging enzymes of active oxygens in chloroplasts was established by localization of the participating enzymes by fractionation of the organella and by immunoelectronmicrosccopy. It was found that the scavenging is proceeded by the thylakoidal and stromal systems. Further, molecular properties of ascorbate peroxidase and monodehydroascorbate reductase were characterized using the purifed enzymes and the overproducing enzymes in Escherichia coli.

在植物暴露于不能利用的明亮阳光的环境条件下，过量的光子产生活性氧，这对植物造成光氧化损伤。为了保护免受这种损害，植物有以下两个放松系统。1.环电子流通过下调光系统II来抑制活性氧的产生，但光还原剂（铁氧还蛋白或NADPH）之间的介体尚未确定。在蓝细菌Synechocystis 6803中，NADPH特异性吡啶核苷酸脱氢酶（NDH）介导电子从NADPH转移到类囊体-质体-醌（PQ），这是通过分析叶绿素荧光和使用NDH-少突变体细胞的P700的氧化还原反应来确定的。此外，在玉米类囊体中，LED阵列分光光度计可检测到一个低氧化还原电位的细胞色素B-559及其参与铁氧还蛋白介导的光系统I周围的循环电子流。介导的光系统周围的循环电子流I.2.叶绿体中活性氧的清除活性氧清除酶的微量比较叶绿体中的氧是通过细胞器的分级分离和免疫电镜对参与酶的定位而确定的。结果表明，这种清除作用是由类囊体系统和基质系统共同完成的。此外，使用纯化的酶和大肠杆菌中过量产生的酶来表征抗坏血酸过氧化物酶和单脱氢抗坏血酸还原酶的分子特性。