Regulation and Physiological Role of Isoprene Emission from Plants

9317900异戊二烯是植物和动物排放的大量物质。许多植物以异戊二烯的形式排放光合作用中固定的碳的2%，使其成为这些植物的主要代谢途径。植物排放的异戊二烯对大气化学有很大影响。异戊二烯排放的代谢控制以及对排放异戊二烯的植物和动物的好处尚不清楚。羟甲基戊二酰辅酶A还原酶(HMGR)对许多异戊二烯类化合物的合成有调节作用，推测异戊二烯排放植物的HMGR活性大部分是合成异戊二烯所必需的。该项目涉及异戊二烯合成的调节，重点是HMGR和最近发现的异戊二烯合成酶。异戊二烯合成所需的HMGR的位置将通过叶绿体分离和叶片物质的非水分离来确定。这项研究将利用最近的发现，即一片叶子上的伤害诱导信号可以传递到另一片叶子上，并在3分钟内将异戊二烯的排放量减少高达80%。将测量创伤信号到达前后HMGR和异戊二烯合酶的活性，以确定异戊二烯合成是如何调节的。这项研究还将利用葛根(pugaria lobata(Wild)Ohwi.)叶片在20摄氏度下生长时不会释放异戊二烯，但30摄氏度的6小时处理可以诱导其释放异戊二烯。将通过探索异戊二烯提供的光合作用机构热保护的最新证据来研究异戊二烯排放的生理作用。需要进行拟议的研究，以确定是否有可能或是否需要改变植物排放的异戊二烯。异戊二烯是合成橡胶的重要原料。目前的市场规模为每年10亿美元。由于异戊二烯的常见替代品巴氏二烯的致癌作用，一种廉价的异戊二烯生物来源可能会对橡胶工业产生重大影响。最后，游离异戊二烯的合成是植物和动物的主要代谢途径，到目前为止在很大程度上被忽视了。了解异戊二烯排放的生理相关性可能会带来重要和有用的见解，而这些见解还无法预测。***

9317900 Sharkey Isoprene is emitted from plants and animals in significant quantities. Many plants emit 2% of the carbon fixed in photosynthesis as isoprene making it a major metabolic pathway in these plants. Isoprene emitted from plants substantially affects atmospheric chemistry. The metabolic control of isoprene emission and the advantage to plants and animals which emit isoprene are unknown. The regulation of synthesis of many isoprenoids is affected by hydroxymethylglutaryl CoA reductase (HMGR) and it is speculated that most HMGR activity of isoprene emitting plants is required for isoprene synthesis. This project deals with the regulation of isoprene synthesis, focusing on HMGR and the recently discovered isoprene synthase. The location of the HMGR needed for isoprene synthesis will be determined by chloroplast isolation and by nonaqueous fractionation of leaf material. The research will exploit recent discovery that a wound-induced signal in one leaf can travel to a second leaf and reduce the rate of isoprene emission by as much as 80% within 3 minutes. The activity of HMGR and isoprene synthase before and after the arrival of this wound signal will be measured to determine how isoprene synthesis is regulated. The research will also exploit the discovery that kudzu (Pueraria lobata (Willd) Ohwi.) leaves do not emit isoprene when grown at 20 degree centigrade but can be induced to emit isoprene by a 6 hour treatment of 30 degree centigrade. The physiological role of isoprene emission will be investigated by exploring the recent evidence of thermal protection for the photosynthetic apparatus provided by isoprene. The proposed research is needed to determine whether it will be possible or desirable to modify isoprene emission from plants. Isoprene is an important raw material for synthetic rubber synthesis. The current market is one billion dollars per year. Because of carcinogenicity of the common substitute for isoprene, batadiene, an inexpensive biogenic source of isoprene could have a large impact on the rubber industry. Finally, the synthesis of free isoprene is a major metabolic pathway in plants and animals which has been largely overlooked until now. Understanding the physiological relevance of isoprene emission may lead to important and useful insights which cannot yet be predicted. ***