A Novel Isourazole Herbicide, Fiuthiacet-Methyl, is a Potent Inhibitor of Protoporphyrinogen Oxidase after Isomerization by Glutathione S-Transferase : PROTEINS, ENZYMES AND METABOLISM

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A novel isourazole herbicide, fluthiacet-methyl (methyl [[2-chloro-4-fluoro-5-[(5,6,7,8-tetrahydro-3-oxo-1H,3H- [1,3,4]thiadiazolo [3,4-α] pyridazin- I -ylidene)amino] phenyl] thio] acetate; experimental code name, KIH-9201) promoted the leakage of electrolytes from cotyledons of velvetleaf (Abtilon theophtasti Medic) and cotton (Gossypium hirsutum L.) plants that are sensitive to this compound. It induced the accumulation of protoporphyrin IX in cotyledons of cotton and inhibited Chl biosynthesis in cotyledons of velvetleaf and cotton at low concentrations (I_<50> values, 10-12 nM). Fluthiacet-methyl was converted to its urazole by glutathione S-transferase that had been partially purified from velvetleaf. The urazole inhibited protoporphyrinogen oxidase (Protox, EC 1.3.3.4) from some plants, including velvetleaf, at low concentrations (150 values, 5.1-11 nM), whereas fluthiacet-methyl was not as potent. The effects in vivo (electrolyte leakage and inhibition of Chl biosynthesis) of fluthiacet-methyl were correlated with the inhibition of Protox activity by the urazole and not with the action of fiuthiacet-methyl itself. From these results, it is concluded that fluthiacet-methyl inhibits Protox activity after conversion to the corresponding urazole by glutathione S-transferase. It is in this way that fiuthiacet-methyl exerts its effect as a light-dependent peroxidizing herbicide.
日本植物生理学会の論文