1,3,4(2H)‐isoquinolinetrione herbicides: Novel redox mediators of photosystem I

Abstract A series of 1,3,4(2 H )‐isoquinolinetriones have been found to be fast‐acting post‐emergence herbicides, producing symptoms of desiccation. These redox‐active compounds are very potent stimulators of the light‐dependent consumption of oxygen at photosystem I in isolated chloroplasts. Pulse radiolysis studies on 2‐ethyl‐1,3,4(2 H )‐isoquinolinetrione have shown it to have free‐radical properties which could enhance the generation of superoxide radicals in plants. Electrochemical studies further support a redox mediator mode of action for the series. The compounds were found to be unstable towards hydrolysis, and this was considered to be a major factor limiting the overall herbicidal effects. Other parameters, related to uptake and/or translocation, which may limit the full expression of the herbicidal activity of certain compounds, are discussed.