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BIOENERGETICS AND PHOTOSYNTHESIS

Changes in Respiratory Mitochondrial Machinery and Cytochrome and Alternative Pathway Activities in Response to Energy Demand Underlie the Acclimation of Respiration to Elevated CO₂ in the Invasive Opuntia ficus-indica^1,[OA]

Unitat de Fisiologia Vegetal, Departament de Biologia Vegetal, Facultat de Biologia, Universitat de Barcelona, Barcelona, Spain 08028 (N.G.-C., J.A.-B.); and Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois 60607 (N.G.-C., E.B.-B., M.A.G.-M.)

Studies on long-term effects of plants grown at elevated CO₂ are scarce and mechanisms of such responses are largely unknown. To gain mechanistic understanding on respiratory acclimation to elevated CO₂, the Crassulacean acid metabolism Mediterranean invasive Opuntia ficus-indica Miller was grown at various CO₂ concentrations. Respiration rates, maximum activity of cytochrome c oxidase, and active mitochondrial number consistently decreased in plants grown at elevated CO₂ during the 9 months of the study when compared to ambient plants. Plant growth at elevated CO₂ also reduced cytochrome pathway activity, but increased the activity of the alternative pathway. Despite all these effects seen in plants grown at high CO₂, the specific oxygen uptake rate per unit of active mitochondria was the same for plants grown at ambient and elevated CO₂. Although decreases in photorespiration activity have been pointed out as a factor contributing to the long-term acclimation of plant respiration to growth at elevated CO₂, the homeostatic maintenance of specific respiratory rate per unit of mitochondria in response to high CO₂ suggests that photorespiratory activity may play a small role on the long-term acclimation of respiration to elevated CO₂. However, despite growth enhancement and as a result of the inhibition in cytochrome pathway activity by elevated CO₂, total mitochondrial ATP production was decreased by plant growth at elevated CO₂ when compared to ambient-grown plants. Because plant growth at elevated CO₂ increased biomass but reduced respiratory machinery, activity, and ATP yields while maintaining O₂ consumption rates per unit of mitochondria, we suggest that acclimation to elevated CO₂ results from physiological adjustment of respiration to tissue ATP demand, which may not be entirely driven by nitrogen metabolism as previously suggested.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Nuria Gomez-Casanovas (ngomezca8{at}bio.ub.edu and ngomezca{at}uic.edu).

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.103911

^* Corresponding author; e-mail ngomezca8{at}bio.ub.edu and ngomezca{at}uic.edu.

Received June 13, 2007; accepted July 11, 2007; published July 27, 2007.

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On the Inside

Peter V. Minorsky
Plant Physiol. 2007 145: 1-2. [Full Text]