Effects of rutin and quercetin on mitochondrial metabolism and on ATP levels in germinating tissues of Glycine max

The effects of quercetin and its glycoside rutin, flavonoid compounds widely distributed in higher plants, on mitochondria isolated from soybean hypocotyls and on ATP levels of soybean embryonic axes were, investigated. Quercetin at 0.5 mM, and lower, inhibited respiration with a mixture of substrates composed of NADH, L-malate, succinate and L-glutamate, both in the absence or in the presence of exogenously added ADP. At concentrations higher than 0.5 mM, the effects of quercetin on basal respiration were shifted toward stimulation. Respiration of uncoupled mitochondria was inhibited by quercetin, irrespective of the nature of the substrates. Swelling driven by phosphate uptake was also inhibited by quercetin. Rutin had no effect on isolated mitochondria. The ATP levels of embryonic axes decreased in the presence of either quercetin or rutin. These results indicate that quercetin impairs the respiratory activity of soybean hypocotyl mitochondria by at least three mechanisms: (a) it inhibits substrate oxidation, probably by a direct action on the electron transfer chain; (b) it inhibits phosphate uptake; and (c) it possibly acts as an uncoupler of oxidative phosphorylation at concentrations higher than 0.5 mM. It was concluded that the action of quercetin on energy metabolism in mitochondria might be the cause of the reduction of the ATP levels in embryonic axes.