Effects of the herbicide 2,4-DB and fungicide captan on reactions of mitochondria and chloroplasts.

The effects of the herbicide 4(2,4-dichlorophenoxy)butyric acid (2,4-DB) and fungicide N-(trichloromethyltio)-4-cyclohexene-1,2-dicarboximide (captan) on electron transport processes of mitochondria and chloroplasts have been investigated. Chloroplasts, isolated from spinach leaves (Spinacia oleracea L.), were treated with pesticide prior to the addition of electron acceptor and ADP. White potato (Solanum tuberosum L.) mitochondria were either incubated with pesticide before the addition of substrate, or they were treated with pesticide after the addition of substrate and ADP. Captan inhibited oxidation of malate by mitochondria and acted as an uncoupler. With succinate as sunstrate captan was found to stimulate state 4 respiration, as substrate captan was found to stimulate state 4 respiration, with the loss of coupled phosphorylation only at higher concentrations of fungicide. The herbicide 2,4-DB appeared to be 5 to 10 times less effective than captain. Both compounds inhibited phosphrylation-coupled succinate oxidation at higher concentrations and malate-coupled phosphorylation at lower concentrations. They acted as inhibitors of NADH-cytochrome c reductase. Both pesticides inhibited noncyclic electron transport in chloroplasts. The rate of ferricyanide reduction in the presence and absence of phosphorylating agents was reduced, and although the rate of ATP generation was reduced also, the P/2e ratio was not changed much under the influence of pesticides.