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. Expressed in roots, stems, leaves, cotyledons and flowers. High expression in stamens. Expressed ubiquitously. Not detected during germination. No effect of antimycin A. Up-regulated by ethylene, high light, glucose, cysteine, mannitol, salicylic acid and cold treatments. Belongs to the alternative oxidase family.