Comparative effects of herbicide dicamba and related compound on plant mitochondrial bioenergetics.
The herbicide dicamba (3,6-dichloro-2-methoxybenzoic acid) was evaluated for its effects on bioenergetic activities of potato tuber mitochondria to elucidate putative mechanisms of action and to compare its toxicity with 2-chlorobenzoic acid. Dicamba (4 micro mol/mg mitochondrial protein) induces a limited stimulation of state 4 respiration of ca. 10%, and the above concentrations significantly inhibit respiration, whereas 2-chlorobenzoic acid maximally stimulates state 4 respiration (ca. 50%) at about 25 micro mol/mg mitochondrial protein. As opposed to these limited effects on state 4 respiration, transmembrane electrical potential is strongly decreased by dicamba and 2-chlorobenzoic acid. Dicamba (25 micro mol/mg mitochondrial protein) collapses, almost completely, Deltapsi; similar concentrations of 2-chlorobenzoic acid promote Deltapsi drops of about 50%. Proton permeabilization partially contributes to Deltapsi collapse since swelling in K-acetate medium is stimulated, with dicamba promoting a stronger stimulation. The Deltapsi decrease induced by dicamba is not exclusively the result of a stimulation on the proton leak through the mitochondrial inner membrane, since there was no correspondence between the Deltapsi decrease and the change on the O(2) consumption on state 4 respiration; on the contrary, for concentrations above 8 micro mol/mg mitochondrial protein a strong inhibition was observed. Both compounds inhibit the activity of respiratory complexes II and III but complex IV is not significantly affected. Complex I seems to be sensitive to these xenobiotics. In conclusion, dicamba is a stronger mitochondrial respiratory chain inhibitor and uncoupler as compared to 2-chlorobenzoic acid. Apparently, the differences in the lipophilicity are related to the different activities on mitochondrial bioenergetics.
Peixoto
Francisco
F
Departamento de Química, Universidade de Trás-os-Montes e Alto Douro, 5001 Vila Real, Portugal. fpeixoto@utad.pt
Vicente
Joaquim A F
JA
Madeira
Vítor M C
VM
D002723:Chlorobenzoates / Q000494:pharmacology; D003996:Dicamba / Q000031:analogs & derivatives* / Q000633:toxicity*; D003576:Electron Transport Complex IV / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects*; D006540:Herbicides / Q000633:toxicity*; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D008933:Mitochondrial Swelling / Q000187:drug effects; D009245:NADH Dehydrogenase / Q000378:metabolism; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D010940:Plant Proteins / Q000378:metabolism; D011198:Solanum tuberosum / Q000201:enzymology / Q000378:metabolism*; D013385:Succinate Dehydrogenase / Q000378:metabolism
D002723:Chlorobenzoates; D006540:Herbicides; D010940:Plant Proteins; C060415:2-chlorobenzoic acid; D013385:Succinate Dehydrogenase; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV; D003996:Dicamba