Effects of pesticides on oxidative phosphorylation and electron transfer in potato tuber mitochondria

The monosodium salt of a synthetic auxin (2,4-D), and a quaternary ammonium salt (BrB), were tested on mitochondria isolated from fresh potato tubers. The two compounds inhibited mitochondrial respiration, the quaternary ammonium salt being the most effective. The uncoupling activity of 2,4-D resulted in the loss of energy production. Moreover, 2,4-D inhibited succinate dehydrogenase, malate dehydrogenase and NAD-dependent malic enzyme activities leading to a strong inhibition of electron flow. The mode of action of BrB was shown to be more complex. It was demonstrated that BrB acts on the membrane structure, its effects being concentration-dependent. Thus, low BrB concentrations inhibiting phosphorylation process by impeding phosphate entry to the matrix. In the presence of high BrB concentrations, mitochondrial membranes were permeable to cytochrome c. In addition, BrB efficiency diminished when the mitochondrial protein concentration was increased. Consequently, BrB probably caused, as a detergent, a large disorganization of the mitochondrial membranes.