C4 Photosynthesis: Mechanism and Response to Carbon Dioxide

人们越来越担心未来50年二氧化碳和气温将同步上升的全球气候变化，包括这将如何影响农业和生态系统的问题。植物将二氧化碳吸收为有机物的机制不同，这将影响它们对气候条件变化的响应。一种植物，称为C4植物，具有积累二氧化碳的积极机制（二氧化碳浓缩机制）。它们在全球范围内对生产力做出了重大贡献，它们也是世界上最严重的杂草之一。目前有一些关于C4植物如何受到全球二氧化碳和温度上升的影响的推测，以及它们是受益于还是受到来自其他物种竞争的威胁。这个问题的基础是a)了解C4植物将太阳能转化为三磷酸腺苷的机制，从而为二氧化碳的浓缩机制提供动力；b)确定允许二氧化碳积累并限制其从叶片同化部位泄漏的扩散阻力的大小。将利用野生型苋属植物（一种C4杂草）和由于C4循环缺陷而缺乏二氧化碳浓缩机制的突变体来研究这些目标。另一个目标是确定C4植物对当前，两倍和三倍当前二氧化碳水平下生长的反应，并确定温度和光照强度的相互作用。这将包括测量两种C4植物（苋菜和玉米）以及一种植物（向日葵）的光合速率、叶片膨胀、催化二氧化碳转化为碳水化合物的关键蛋白质的含量和活性。一个主要的问题是C4物种是否能够适应二氧化碳的富集和温度的上升，从而在碳同化的关键过程中保持平衡。

Edwards 9807916 There is growing concern about predicted global climate change with parallel rises in carbon dioxide (C02) and temperature over the next 50 years, including questions of how this will impact agriculture and ecosystems. Plants have different mechanisms of assimilating C02 into organic matter, which will affect their responses to changes in climatic conditions. One type of plants, called C4 plants, have an active mechanism of accumulating C02 (a C02 concentrating mechanism). They make a substantial contribution to productivity on a global scale, and they also account for some of the world's worst weeds. There is currently speculation about how C4 plants would be affected by a global rise in C02 and temperature, and whether they would benefit, or would be threatened intrinscially by competition from other species. Fundamental to this question is a) understanding the mechanism of conversion of solar energy into adenosine triphosphate in C4 plants to power the C02 concentrating mechanism, and b) determining the magnitude of the diffusive resistance which allows the C02 to accumulate and limits its leakage from assimilating sites within the leaf. Wildtype plants of Amaranthus edulis (a C4 weed), and mutants which lack the C02 concentrating mechanism due to a defective C4 cycle, will be used to study these objectives. The other objective is to determine the response Of C4 plants to growth under current, two and three times current levels of C02 and to determine the interactive effects of temperature and light intensity. This will include measurements of photosynthetic rates, leaf expansion, content and activity of key proteins which catalyze conversion of carbon dioxide into carbohydrates in two C4 species, Amaranth and maize (corn), and one species, sunflower. A major question is whether C4 species can acclimate to C02 enrichment and rising temperatures and, thus, maintain a balance between key processes in carbon assimilation.