ACIFLUORFEN-METHYL EFFECTS ON PORPHYRIN SYNTHESIS IN LEMNA-PAUSICOSTATA HEGELM-6746

Acifluorfen-methyl jmethyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate) (0.1-1 μM) caused electrolyte leakage from Lemna pausicostata plants after a 2-h lag when treated in white light (500 μE m-2s-1). When treated in darkness for 20 h and then exposed to light, herbicidal damage developed slowly compared with that in plants exposed to light and herbicide simultaneously. In light, acifluorfen-methyl caused an almost 100-fold accumulation of protoporphyrin IX during the first 2 h of treatment, followed by a decline in content. Protochlorophyllide levels in light were decreased by the herbicide. There was no effect on Mg-protoporphyrin IX, coproporphyrin, or uroporphyrin content. In darkness, protoporphyrin IX accumulation in herbicide treatments reached only 20-25% of that occurred in the light. Exogenous sucrose had no effect on dark accumulation of any porphyrin in any treatment. Ex ogenous hemin significantly reduced the efficacy to the herbicide. These data indicate that protopor phyrin IX is the only photodynamic compound causing herbicidal damage in acifluorfen-methyltreated plants and that the herbicide is much more effective in light than in darkness because of a greater capacity to synthesize porphyrins in light. © 1990, American Chemical Society. All rights reserved.