| Abstract: | The effect of six phenoxy-acid herbicides, 4-chloro-2-methylphenoxyaceticacid (MCPA), 4-(4-chloro-2-thylphenoxy)butyric acid (MCPB),2, 4-dichlorophenoxyacetic acid (2, 4-D), 4-(2, 4-dichlorophenoxy)butyricacid (2, 4-DB), 2, 4, 5-trichlorophenoxyacetic acid (2, 4, 5-T),and 4-(2, 4, 5-trichlorophenoxy)butyric acid (2, 4, 5-TB) onoxidative phosphorylation of mitochondria isolated from younghypocotyls of Vicia faba L. has been investigated. When NADHwas used as substrate all the test herbicides were found tostimulate state 4 respiration with the loss of phosphorylationand respiratory control in varying degrees. When malate andsuccinate were used separately as substrates, treatment with2, 4-DB, 2, 4, 5-T, and 2, 4, 5-TB at low concentration resultedin a marked stimulation of state 4 respiration; this effectwas not obtained with MCPA, MCPB, or 2, 4-D. At higher concentrationsall herbicides strongly inhibited respiration. These compoundsreleased oligomycin inhibition during NADH oxidation in varyingdegrees, stimulated mitochondrial adenosine-triphosphatase activity,and induced swelling of isolated mitochondria. In many respectsand in differing degrees they resemble 2, 4-dinitrophenol (DNP)in their action as uncouplers. Phenoxy-butyric acids were foundto be more toxic in vitro as uncouplers than their correspondingphenoxyacetic acids. Phenoxyacetic acids were very active as uncouplers in vivo whilephenoxybutyric acids had negligible effect. It is concludedthat in vivo, non-activity of phenoxybutyric acids is due totheir restricted entry into plants and that if available atthe site of action they would be inherently toxic. |
