Molecular Mechanisms of Tolerance to Reactive Oxygen Species and Its Induction in Weeds

本研究旨在阐明植物（包括杂草）对环境胁迫特别是天然和合成化学物质引起的光氧化损伤的耐受性的生理和分子机制。长喙沙蒿积极吸收根中的Na、Cl离子并将其转运到地上部分。因此，在这个物种的地上部细胞的应力缓解机制进行了研究。高浓度的离子增加了细胞中活性氧（ROS）的产生。长喙沙枣具有较高的抗氧化酶组成水平，盐胁迫显著诱导了这些酶的活性，缺镁条件下生长的植物对ROS的耐受性增强，抗氧化酶活性尤其是胞浆型抗坏血酸过氧化物酶活性增强。该基因的诱导机制正在研究中，对引起光下细胞过氧化损伤的化学物质的作用方式和耐受机制进行了研究。为了阐明活性氧参与除草剂二氯喹啉酸的植物毒性作用，建立了H_2O_2的定量方法。由于ROS具有非常高的反应性，因此很难鉴定ROS种类。但我们成功地用荧光法测定了特定植物中的H_2O_2。我们还研究了利用ESR技术鉴定植物细胞中活性氧的方法。该化合物通过黑色素合成途径产生的活性氧（ROS）对拟南芥产生氧化损伤。L-DOPA在植物物种之间的选择性作用是由于负责ROS产生的多酚氧化酶的差异活性。

This study was aimed to elucidate physiological and molecular mechanisms of tolerance of plants including weeds to environmental stress especially to photo-oxidative injury caused by natural and synthetic chemicals.Leguminous weed Sesbania rostrata has tolerance to 0.5% NaCl. S.rostrata actively absorbed Na and Cl ions from roots and translocated them to aboveground parts. Therefore, mechanisms of stress alleviation in shoot cells of this species were investigated. High concentrations of the ions increased the production of reactive oxygen species (ROS) in the cells. S.rostrata has higher constitutive levels of antioxidative enzymes and these enzyme activities were remarkably induced by the salt-stress.Plant species grown with magnesium-deficient condition showed greater tolerance to ROS with increased antioxidative enzyme activities especially cytosolic isoform of ascorbate peroxidase. Induction mechanism of this gene is under examination.The mode of actions of the chemicals that caused the peroxidation injury of the cells in the light and the mechanism of tolerance were investigated. To clarify ROS involvement in phytotoxic action of herbicide quinclorac, quantification methods of H_2O_2 has been established. Since ROS has very high reactivity, identification of ROS species is difficult. However, we succeeded H_2O_2 determination with the chemiluminescent method in specific plant species. We also studied ROS identification in plant cells by using ESR.Leguminous allelopathic plant Mucuna pruriens produces L-DOPA. This compound was elucidated to cause oxidative injury on susceptibel plant spesies by ROS generated from melanin synthesis pathway. Selective action of L-DOPA between plant species is due to differential activity of polyphenol oxidase that is responsible for ROS generation.