Studies ontheModeofAction ofAcifluorfen-Meth yl in Nonchlorophyllous Soybean Cells'

Phytotoxic effects oftheherbicide acifluorfen-methyl onnonchlorophyllous soybean cells wereestimated by86Rbleakage. Anaction spectrum study showedmaximuminjury at350to450nanometers, withlesser activity between 450and700nanometers. Cells treated inthedarkwith acifluorfen-methyl accumulated fluorescent pigments withthespectral characteristics ofprotoporphyrin IX.Theaction spectrum ofacifluorfenmethyl matched theabsorption spectrum ofthistetrapyrrole, andthe extent ofcellular damageinthelight wasrelated tothedegree offluorescent pigment accumulation. We propose thatthephytotoxicity of diphenyl ether herbicides couldbeexplained bytheir ability tocause abnormal accumulations oftetrapyrroles, whichinturninduce lethal photooxidative reactions.