Poster: Respiratory pathways

Abs # 213: Transgenic manipulation of cyanide-resistant alternative oxidase levels affects growth of Arabidopsis at low temperature.

Presenter:	Umbach, Ann L., umbacha@acpub.duke.edu
Authors	Fiorani, Fabio  (A) (B)  Umbach, Ann L. (A)   Siedow, James N. (A)
Affiliations:	(A): DCMB Group/ Biology Department, Duke University, Durham, NC, U.S.A. (B): Department of Plant Systems Biology, Flemish Interuniversity Institute for Biotechnology (VIB) ,University of Ghent, Belgium

The mitochondrial alternative oxidase (AOX) of plants competes with the standard cytochrome pathway for electrons by directly reducing O₂ to H₂O without associated ATP synthesis. This pathway can use electrons in excess of cytochrome pathway capacity, thereby decreasing reactive oxygen species (ROS) production from the ubiquinone pool. Under stressful conditions where mitochondrial ROS levels are known to increase, AOX may be important for plant performance and survival. We have used transformed Arabidopsis thaliana to test this hypothesis. Three classes of transformants (overexpressers of wild-type AOX and of a mutated constitutively active AOX, and plants anti-sense for AOX) were grown with wild-type at 12^oC day/8^oC night. In the rosette stage, relative to wild-type, anti-sense plants showed a marked reduction in total leaf area (-22 to -33%) and rosette diameter (-10 to -30%), while AOX overexpressers had greater total leaf area (+33 to +55%) and larger rosette size (+10 to +20%). Lines overexpressing the constitutively active AOX had leaf areas and rosette diameters intermediate between those of wild-type and the wild-type AOX overexpressers. The size differences persisted during the first four weeks of growth. Plants with elevated AOX also produced more anthocyanins and had lower levels of thiobarbituric acid-reactive substances, indicating decreased ROS production. None of these differences were detected in plants grown at 23^oC. These results are the first examples, to our knowledge, of whole-plant phenotypes associated with changes in AOX levels and demonstrate that AOX function can improve plant growth at low temperature. The molecular mechanisms involved in these responses are currently under investigation. Supported by NSF grant MCB 0091080.