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 roots, leaf sheaths and leaf blades. Expressed in anthers at the uninucleate microspore stage and the bicellular pollen stage. Induced by cold (PubMed:12012245, PubMed:12036102, PubMed:22994594). Induced by drought and salt stresses, heat shock, hydrogen peroxide and methyl viologen (PubMed:22994594). Down-regulated under oxygen deprivation (PubMed:10767423). Belongs to the alternative oxidase family.