Uptake, Translocation, Subcellular Distribution, and Metabolism of Fluoxapiprolin in Cucumber Plants

Abstract Fluoxapiprolin is an oxysterol-binding protein fungicide that exhibits high efficacy against cucumber downy mildew; however, its metabolites may be more toxic than the parent compound. In this study, we examined its uptake, translocation, subcellular distribution, and metabolism in cucumbers. Fluoxapiprolin primarily accumulated in roots through aquaporin-mediated passive absorption and apoplastic transport and showed poor upward translocation. The behavior of the five metabolites varied. BCS-DE72761 and BCS-DE61185 accumulated continuously in leaves, whereas BCS-BP32808 exhibited the strongest upward translocation. In roots and stems, 88–100% of the metabolites were distributed in soluble components. Fluoxapiprolin was primarily transformed via amide bond cleavage into BCS-CC26101, the reversible interconversion of BCS-DE61185 and BCS-DE72761 through amidation and hydrolysis, as well as the transformation of BCS-BP32808 into multiple metabolites. These reactions can alter the physicochemical properties of the compounds, thereby significantly affecting their translocation in plants. Our findings provide a theoretical basis for scientific application and risk assessment of these compounds.