Abstract:When etiolated seedlings of mung bean (Phaseolus radiates L.) were treated with exogenous ethylene at 25℃, the respiratory peak of hypocotyl mitochondria appeared earlier, the maximum of the respiration was higher than the control, and the rate of cyanide-resistant electron transport pathway increased more rapidly than that of the cytochrome pathway. After the respiratory rate was decreased for a long time (15 h), the rate of production of superoxide radical (O2-.) still kept rising. To test the role of superoxide radical in accelerating respiration，the effect of exogenous superoxide radical which was generated from the system of xanthine and xanthine oxidase on respiration was examined．It was found that the respiratory peak also appeared earlier than the control．Acoording to the above result，we draw a conclusion that ethylene stimulates the rate of mitochondrial respiration that is due to the increase of the O2-. production rate，through stimulating the rate of electron leak of respiratory chain． This may he one of the mechanisms of the effect of ethylene on mitochondrial respiration.