Cloning of an Additional cDNA for the Alternative Oxidase in Tobacco

The alternative oxidase is a cyanide-insensitive termi- nal oxidase found in a variety of organisms although it is best characterized in plants. It branches from the Cyt chain at the level of ubiquinone and does not pump protons and is thus non-energy-conserving. In thermo- genic floral appendages it plays a clear role in the vola- tilization of compounds to attract insects for pollination, but its role in nonthermogenic plants is unclear (Moore and Siedow, 1991). Induction of the alternative oxidase at the gene level has been characterized in a number of studies with compounds that inhibit the Cyt chain. Ad- ditionally, aging of potato slices, treatment with ethylene in fruits and storage tissue, cold treatment in tobacco (Nicofiana fobacum) and wheat, and salicylic acid treat- ment of Sauromatum guttatum have a11 been shown to induce the alternative oxidase (Day et al., 1995). At the biochemical level allosteric stimulation by pyruvate and the oxidation reduction state of the protein have been shown to be important determinants of activity (Millar et al., 1993; Umbach and Siedow, 1993).