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. Maximally expressed in dry seeds. Detected in roots, stems and leaves. Expressed predominantly during early stages of germination with maximum level at 12 hours after imbibition and at the latter stages of silique maturation. Accumulates in dry seeds. No effect of antimycin A, ethylene or cold treatments. Up-regulated by paraquat and cysteine treatments, but down-regulated by erythromycin, citrate, glucose and H(2)O(2) treatments. Belongs to the alternative oxidase family.