Catalyzes the cyanide-resistant oxidation of ubiquinol and the reduction of molecular oxygen to water, but does not translocate protons and consequently is not linked to oxidative phosphorylation. May increase respiration when the cytochrome respiratory pathway is restricted, or in response to low temperatures. 2 a ubiquinol + O2 = 2 a ubiquinone + 2 H2O Binds 2 iron ions per subunit. Homodimer; disulfide-linked. Expressed in leaves and panicles. Is not induced either by drought, cold and salt stresses, or heat shock. Belongs to the alternative oxidase family.