Inhibition of plant protoporphyrinogen oxidase by the herbicide acifluorfen-methyl

The effect of acifluorfen-methyl on tetrapyrrole synthesis in greening chloroplasts of Cucumis sativus was examined. Formation of Mg-proto-porphyrin IX from δ-aminolevulinate was reduced 98% by 10 micromolar acifluorfen-methyl. Conversion of protoporphyrin IX to Mg-protoporphyrin IX was unaffected, but protoporphyrin IX synthesis from δ-aminolevulinate was blocked, indicating a site of inhibition prior to the Mg-chelatase. The enzymic oxidation of protoporphyrinogen IX to protoporphyrin IX was highly sensitive to acifluorfen-methyl, indicating that the site of action of the herbicide is the protoporphyrinogen oxidase. (© 1989 FMC Corporation. All rights reserved.)