Effects of Diphenylether Herbicides on Reactions of Mitochondria and Chloroplasts

Abstract

Effects of three diphenylether herbicides [2,4-dichlorophenyl-p-nitrophenyl ether (nitrofen); 2,4,6-trichlorophenyl-4′-nitrophenyl ether (hereinafter referred to as MC-1478); and 2,4′-dinitro-4-trifluoromethyl-diphenylether (hereinafter referred to as C-6989)] were measured on phosphorylation and electron transport in spinach(Spinacia oleraceaL.) chloroplasts, and mung bean(Phaseolus aureusL., var. Jumbo) and white potato tuber(Solarium tuberosumL.) mitochondria. All of the diphenylethers acted primarily as inhibitors of chloroplast noncyclic electron transport, and the coupled photophosphorylation. The compounds ranked in the following decreasing order of inhibitory effectiveness: MC-1478 ≥ C-6989 >> nitrofen. A site of action close to light reaction II was suggested. At high molar concentrations, marginal interference with cyclic electron transport or phosphorylation was obtained. In mitochondria, MC-1478 and nitrofen acted primarily as electron transport inhibitors with malate, NADH, and succinate as substrates. MC-1478 was a slightly stronger inhibitor than nitrofen. Only slight stimulation of ADP-limited oxygen uptake was obtained during the oxidation of NADH and succinate; whereas, strong inhibition of oxygen uptake was obtained with malate. C-6989 also weakly stimulated ADP-limited oxygen uptake with NADH and succinate but differed from the two chlorinated diphenylethers in that electron transport was not inhibited when ADP was present in excess. Interference with ATP generation could be one of the mechanisms through which the phytotoxicity of diphenylether herbicides is expressed.

Penetration, Translocation, and Metabolism of Acifluorfen in Soybean (Glycine max), Common Ragweed (Ambrosia artemisiifolia), and Common Cocklebur (Xanthium pensylvanicum)

“…Common ragweed, being unable to metabolize acifluorfen into a non -toxic form, is most susceptible. The parent herbicide can inhibit specific metabolic processes as suggested by Moreland et al (16). Soybeans, on the other hand, may metabolize acifluorfen into a non-toxic form.…”

“…Faster degradation within peanuts, and greater acropetal translocation within cucumber, could account for the difference in susceptibility of the two species. In susceptible cucumber, more of the parent compound would reach the possible site of action in the chloroplasts, as proposed by Moreland et al (16).…”

Site of Action of Oxyfluorfen

“…The full chain electron transport H 2 0 ~* MV showed a maximum inhibition of about 30% for the uncoupled reaction and about 40% for the coupled reaction at oxyfluorfen con centrations of 5 X 10" 5 and 2.5 X 10" 5 M, respectively ( Figure 4). Other researchers (7,21) found 50% inhibitions of electron transport by various diphenylethers at concentrations of 1 to 7 X 10" 5 M.…”

“…Several researchers (7,21) have shown that diphenylethers inhibit photosynthetic electron transport in isolated chloro plasts by 50% at concentrations between 1 and 5 X 10" 5 M. Bugg et al (7) have suggested that the site of electron trans port inhibition by diphenylethers is in the region of plastoquinone and cytochrome f (Figure 1). Moreland et al (21) suggested that interference with ATP generation could be one mechanism of diphenylether phytotoxicity.…”

The Bleaching Effect of the Diphenyl Ether Oxyfluorfen

“…Apparently there is a conversion process in which xanthophylls, but not photosynthetic electron transport, were reported to be involved (8,19). The light effect ma~be an indirect one, because it has been shown that some diphenyl ethers in comparatively high concentration may interfere with linear photosynthetic electron transport and subsequently prevent non-cyclic phosphorylation (21). We.…”