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

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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.