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 (By similarity). 2 a ubiquinol + O2 = 2 a ubiquinone + 2 H2O Binds 2 iron ions per subunit. Homodimer; disulfide-linked. Mitochondrial, possibly in the inner surface of the inner mitochondrial membrane. Continuous increase of expression in developing cotyledons until day 20. Belongs to the alternative oxidase family.