Specific Binding of Protoporphyrin IX to a Membrane-Bound 63 Kilodalton Polypeptide in Cucumber Cotyledons Treated with Diphenyl Ether-Type Herbicides

Abstract

Porphyrin accumulation in excised cucumber cotyledons (Cucumis sativus L.) treated with a N-phenylimide S-23142 (N-[4-chloro-2-fluoro-5-propargyloxyphenyl]-3,4,5,6-tetrahydrophthalimide) and a diphenylether acifluorfen-ethyl (ethyl-5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitro benzoic acid) was studied. Most of the accumulated porphyrins were found in the membrane fractions of 6,000g and 30,000g pellets, forming a complex with a membrane polypeptide. The complex was solubilized with 1% n-dodecyl f-D-maltoside and its molecular mass was estimated to be 63,000 and 66,000 daltons by sodium dodecyl sulfatepolyacrylamide gel electrophoresis and gel permeation high performance liquid chromatography (HPLC), respectively. The polypeptide also existed in untreated cotyledons but had little protoporphyrin IX. The complex was also formed in vitro by mixing the 30,000g pellets from untreated cotyledons and authentic protoporphyrin IX. However, protoporphyrin IX formed the complex specifically with the 63,000 dalton polypeptide and not with the other proteins both in vivo and in vitro. At least four fluorescent porphyrins, including protoporphyrin IX, were found in the acetone extract of the cotyledons by HPLC using a reversed phase column. Protoporphyrin IX was one of the two porphyrins that formed the complex. These results suggest that S-23142 and acifluorfenethyl enhance the accumulation of protoporphyrin IX, which forms the complex with the membrane protein.

Physiological basis for CGA-248757 and flumiclorac selectivity in five plant species

“…CGA-248757 and flumiclorac are cyclic imide herbicides that selectively control broadleaf weeds postemergence (POST) in Zea mays and Glycine max (Kamoshita et al 1993;Porpiglia et al 1994). Despite their different chemical structures, CGA-248757 and flumiclorac have a mode of action similar to diphenyl ether, oxadiazole, and triazolinone herbicides (Sato et al 1991). These herbicides inhibit the protoporphyrinogen oxidase (Protox) enzyme in susceptible plant species that leads to an uncontrolled nonenzymatic oxidation of protoporphyrinogen IX (Protogen) to protoporphyrin IX (Proto) (Anonymous 1995;Duke et al 1991;Mito et al 1991).…”