Acclimation of leaves to long-term changes in temperature: does it alter the efficiency of respiratory energy production?

Temperature-mediated changes in plant respiration will be critical in determining the extent to which atmospheric carbon dioxide will be sequestered by the biosphere in a future, warmer world. This is because, on a global scale, plant respiration releases nearly ten times more carbon dioxide (one of the greenhouse gases responsible for global warming) than does the burning of fossil fuels etc. At the individual plant level, plant respiration releases into the atmosphere between 25-80% of the carbon dioxide previously fixed by photosynthesis. This release of carbon dioxide is not all wasteful, however, as coupled to the release of respiratory carbon dioxide is the production of energy necessary for the growth and survival of plants. Critical in determining the efficiency of respiratory energy production (i.e. the amount of energy produced per unit carbon dioxide released) is whether respiration in the mitochondria take place via the energy-producing how cytochrome oxidase (Cox) pathway or the energy-wasting, alternative oxidase (Aox) pathway. Understanding how environmental change impacts on the activity of these two pathways in intact tissues is critical to ascertaining whether climate-dependent alterations in respiratory CO2 release are coupled to changes in the production of ATP. If the efficiency of ATP synthesis does vary with climate, this could have profound implications for the growth rate and competitive ability of plants growing in natural environments. In this project, we will establish whether changes in temperature alter the ratio of Cox to Aox activity in intact leaves. Although we know that both the Aox and Cox pathways are temperature-sensitive, our understanding of how short- and long-term changes in temperature impact on activity of the Aox and Cox pathways in intact leaves remains limited. Understanding the extent to which Aox and Cox pathway activity vary with temperature is essential if we are predict the extent to which climate-dependent changes respiratory carbon dioxide release are coupled to changes in the production of respiratory energy necessary for plant growth/survival. We will use a cold-tolerant forb (Arabibopsis thaliana) in our experiments, as we know that this species is capable of adjusting respiration rates when challenged with a wide range of growth temperatures. Use of Arabidopsis will also enable studies of respiration rates in intact tissues to be linked to studies of gene-expression and protein synthesis. The project will be a collaboration between the University of York and the Australian Research Council Centre of Excellence (CoE) in Plant Energy Biology; the CoE has one of a few mass spectrometer systems in the world capable of measuring rates of Aox and Cox pathway in intact leaves. Given that the CoE will cover all plant growth/consumable costs, the proposal therefore represents excellent value for money for NERC and an opportunity to achieve an outcome that is not possible within the UK.