| Summary: | The susceptibility of isolated maize mitochondria to the growth regulators: 2,4-dichlorophenoxyacetic acid (2,4-D) and abscisic acid (ABA) was studied. It was found that 2,4-D (a herbicide) inhibits respiration in mitochondria, as do other herbicides or phenoxy-acids. In the entire range of concentrations used (10-3-10-9 M), 2,4-D introduced into the medium before the respiration reaction was begun, or during it, limited the intensity of succinate oxidation. It did not, however, markedly change phosphorylation properties. Uncoupling of oxidative phosphorylation took place only after preincubation of mitochondria with 2,4-D and was the result of the destruction of mitochondrial membranes. ABA (a growth inhibitor of plants) caused a similar response in maize mitochondria. Preincubation of mitochondria with ABA lead to the uncoupling of oxidative phosphorylation. Whereas ABA introduced during respiration (state 4 respiration) or before its onset, lowered the oxidative potential of mitochondria, it also changed the pattern of state 4-3-4 transition after addition of ADP (it was especially visible at high concentrations), which indicates that the coupling of oxidative phosphorylation with the respiratory chain has faltered. It seems that this negative effect of 2,4-D and ABA on respiration of isolated maize mitochondria is connected with the inhibitory effect of these growth regulators on the growth of maize coleoptiles. Interference in the organization mitochondrial membranes results in a lowered supply of ATP - a source of energy needed in elongation processes.
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