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Published on July 27, 2007; 10.1104/pp.107.103911

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Received June 13, 2007
Accepted July 11, 2007

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

Nuria Gomez-Casanovas *, Elena Blanc-Betes , Miquel A.Gonzalez-Meler , and Joaquim Azcon-Bieto.

Unitat de Fisiologia Vegetal, Departament de Biologia Vegetal, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal, 645, Barcelona, Spain, 08028; Department of Biological Sciences, University of Illinois at Chicago 845 W. Taylor Street M/C 066, Chicago IL, USA 60607

* Corresponding author; email: ngomezca8{at}bio.ub.edu.

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 CAM Mediterranean invasive Opuntia ficus-indica (L.) Miller was grown at various CO2 concentrations. Respiration rates, maximum activity of Cyt 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 cyt 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.






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