Molecular Mechanisms Controlling Plant Responses to ElevatedCarbon Dioxide

9420054西曼地球大气中的二氧化碳浓度预计到世纪中期到末期将翻一番。 这一变化将对自然和农业生态系统产生重大影响，主要是因为二氧化碳对光合作用的影响，光合作用是全球碳循环中的主要生物过程。 在许多植物物种中，在大气二氧化碳浓度升高的条件下长期生长会导致光合机构的绝对光合能力和蛋白质组成发生实质性变化。 然而，外部二氧化碳浓度作用于基因表达水平的分子机制在很大程度上是未知的。 本研究的总体目标是将二氧化碳对光合生理过程（如叶片气体交换）和生化过程（如Rubisco蛋白水平和活性调节）的影响与Rubisco基因表达和特定碳水化合物水平的变化联系起来，以确定控制植物对二氧化碳浓度升高的反应的分子机制。 拟南芥（野生型和现有突变体）将用作模型植物系统。 具体目标是： (1)研究了不同发育阶段大气二氧化碳浓度对拟南芥Rubisco大亚基（rbcL）和小亚基（rbcS）基因表达、Rubisco全酶水平、激活状态、RuBP库大小以及光合作用对胞间二氧化碳分压（Ci）的响应的影响（低于环境温度、环境温度、两倍环境温度、饱和）。 (2)通过利用（1）具有改变的源或库活性的拟南芥突变体，鉴定在大气二氧化碳浓度和Rubisco基因表达之间的信号转导途径中起作用的细胞信号（改变叶片碳水化合物代谢，不产生种子，改变根冠比，延迟开花时间）在研究二氧化碳对Rubisco基因表达和光合作用的影响，和;（2）糖对rbcS启动子-GUS构建体瞬时表达的影响。

9420054 Seemann The concentration of carbon dioxide in the earth's atmosphere is projected to double by the middle to end of the 21st century. This change will have substantial effects on natural and agricultural ecosystems, primarily because of the effect of carbon dioxide on photosynthesis, the major biological process in the global carbon cycle. In many plant species, long-term growth at elevated atmospheric carbon dioxide results in the substantial change in both absolute photosynthetic capacity and the protein composition of the photosynthetic apparatus. However, the molecular mechanism(s) by which external carbon dioxide concentration acts at the level of gene expression, are largely unknown. The overall objective of this research is to link carbon dioxide effects on photosynthetic physiological processes (e.g. leaf gas exchange) and biochemical processes (e.g. rubisco protein level and regulation of activity) to changes in both rubisco gene expression and specific carbohydrate levels in order to identify molecular mechanisms which control the response of plants to elevated carbon dioxide. Arabidopsis thaliana (wild-type and existing mutants) will be used as the model plant system. Specific objectives are: (1) Determine the effect of atmospheric carbon dioxide concentration during different developmental stages on rubisco large subunit (rbcL) and small subunit (rbcS) gene expression, rubisco holoenzyme level, activation state, RuBP pool size and the response of photosynthesis to intercellular carbon dioxide partial pressure (Ci) in Arabidopsis thaliana grown at and switched between a number of carbon dioxide concentrations (subambient, ambient, twice ambient, saturating). (2) Identify the cellular signal(s) that function(s) in the signal transduction pathway between atmospheric carbon dioxide concentration and rubisco gene expression by utilizing (1) mutants of Arabidopsis thaliana with altered source or sink activities (altered leaf carbohydra te metabolism, no seed production, altered root:shoot ratio, delayed flowereing time) in studies of carbon dioxide effects on rubisco gene expression and photosynthesis, and; (2) transient expression studies of carbohydrate effects on rbcS promoter-GUS constructs.