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

在未来变暖的世界里，由温度调节的植物呼吸变化将是决定大气二氧化碳在多大程度上被生物圈隔离的关键。这是因为，在全球范围内，植物呼吸释放的二氧化碳(导致全球变暖的温室气体之一)几乎是燃烧化石燃料等的十倍。在单个植物层面上，植物呼吸释放到大气中的二氧化碳占之前光合作用固定的二氧化碳的25%-80%。然而，这种二氧化碳的释放并不完全是浪费，因为呼吸二氧化碳的释放是植物生长和生存所必需的能量的生产。决定呼吸能量产生效率(即每单位释放的二氧化碳产生的能量)的关键是线粒体中的呼吸作用是通过产生能量的细胞色素氧化酶(COX)途径还是能量消耗的交替氧化酶(AOX)途径发生的。了解环境变化如何影响完整组织中这两条途径的活动，对于确定呼吸二氧化碳释放的气候相关变化是否与ATP产生的变化有关至关重要。如果ATP合成的效率确实随着气候的变化而变化，这可能会对生长在自然环境中的植物的生长速度和竞争力产生深远的影响。在这个项目中，我们将确定温度的变化是否会改变完整叶片中COX/AOX活性的比率。虽然我们知道AOX和COX途径都是温度敏感的，但我们对温度的短期和长期变化如何影响完整叶片中AOX和COX途径的活性的了解仍然有限。了解AOX和COX途径活性随温度变化的程度是至关重要的，如果我们要预测呼吸二氧化碳释放与植物生长/生存所需呼吸能量产生的变化在多大程度上与气候相关的变化。在我们的实验中，我们将使用一种耐寒的叉树(Arabibopsis Thaliana)，因为我们知道，当面临广泛的生长温度挑战时，这种物种能够调整呼吸速率。利用拟南芥还将使完整组织中呼吸速率的研究与基因表达和蛋白质合成的研究联系起来。该项目将是约克大学和澳大利亚研究委员会卓越中心(COE)在植物能源生物学方面的合作；COE拥有世界上少数几个质谱仪系统之一，能够测量完整叶片中AOX和COX途径的速率。鉴于COE将涵盖所有植物生长/消耗品成本，因此，该提案对NERC来说代表着极高的性价比，并提供了一个实现在英国境内不可能实现的结果的机会。

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.