Positional Isomers of Aryloxyphenyl Cyanurates Have Different Sites of Action

Site of action of aryloxyphenyl cyanurate analogues was found to vary significantly depending upon the placement of cyanurate moiety. Plants treated with the analog having the cyanuric acid in the para-position showed chlorosis and took 2-3 days before the first necrotic symptoms appeared. Additional tests indicated that this compound is a strong photosystem II inhibitor. In contrast, plants treated with the analog having cyanuric acid in the meta-position exhibited necrosis within a few hours after treatment. Further tests revealed that this compound is a potent inhibitor of protoporphyrinogen oxidase. Therefore, depending upon the placement of cyanuric acid, the site of action of these herbicidally active compounds changes substantially. These results also show that aryloxyphenyl cyanurates are new classes of PSII and PROTOX inhibitors.