Regulation of mitochondrial activity by indoleacetic acid

Mitochondria of scutella of a maize inbred were allowed to respire in the presence of indoleacetic acid. Greatest enhancement of , P/N and P/O was observed with indoleacetic acid concentration around 1.07 · 10⁻¹⁰ M. At concentrations above 1.07 · 10⁻⁸ M, O₂ uptake was greatly inhibited while phosphorylation was inhibited to a lesser degree. It was shown that enhancement of mitochondrial activity is dependent on CoA; without added CoA, effects of indoleacetic acid were slight. The most effective concentration of CoA was shown to be 0.1 mg/2.8 ml reaction mixture. In the presence of 1.07 · 10⁻¹⁰ M indoleacetic acid, rate of O₂ uptake measured at 3-min intervals was greatly increased. In addition, with indoleacetic acid in the reaction mixture, mitochondria showed an almost immediate enhancement of activity while the control reaction and the reaction with high concentration of indoleacetic acid (1.07 · 10⁻⁵ M) exhibited a lag of 3–4 min. With regard to the relationship of CoA and indoleacetic acid-induced stimulation of rate of mitochondrial O₂ uptake, two points were observed: without added CoA, the rate of O₂ uptake is sharply reduced and there is a lag of 7 min before mitochondria show any O₂ uptake.

The results suggest that indoleacetic acid enhances mitochondrial activity by affecting the enzyme(s) of the oxidative phosphorylation pathway. It is suggested that indoleacetic acid accomplishes such enhancement by acting as an allosteric effector.