The Role of Xanthophylls in the Mechanism of Nonradiative Energy Dissipation in Photosynthesis

叶黄素在光合作用非辐射能量耗散机制中的作用

• 批准号: 9816759
• 负责人: Harry Frank
• 金额: $ 30.6万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-02-01 至 2003-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9816759&HistoricalAwards=false
• 关键词: Role; Xanthophylls; Mechanism; Nonradiative; Energy

Harry A. Frank9816759Photosynthetic organisms contain protective mechanisms by which excess light energy is dissipated before it leads to the photodestruction of the photosynthetic apparatus. Also, energy flow from the light-harvesting pigment-protein complexes to the photosynthetic reaction center is highly regulated. The molecular features that control these processes are not well understood. Xanthophyll pigments have been implicated in the mechanisms, but the precise nature of their involvement is unclear. In this project, several different xanthophylls will be studied. The experiments to be performed include steady state and time-resolved absorption and fluorescence spectroscopy and electrochemical determinations. The spectroscopic experiments will measure the efficiencies and dynamics of energy transfer between the xanthophylls and chlorophyll. The electrochemical experiments will reveal the oxidation potentials of the molecules in solution and bound in the pigment-protein complexes. The major objective of this research to examine each of the molecular factors thought to be important in nonradiative energy dissipation in order to reveal the detailed molecular mechanism by which it takes place in vivo. The factors to be explored include xanthophyll composition, state of aggregation, pH, phosphorylation, position of the energy levels, and the oxidation potentials of the pigments. The question of the involvement of the xanthophylls as direct or indirect quenchers of chlorophyll fluorescence will be examined. The hypotheses that xanthophylls quench chlorophyll fluorescence by energy transfer or electron transfer mechanisms will be tested. The experiments are important in enlarging our view of how photosynthetic organisms protect themselves from excessive light energy absorption and respond to varying environmental conditions while maintaining efficient energy flow essential for survival.Xanthophylls are familiar to anyone who has observed the bright orange and yellow colors of Autumn leaves in New England. However, unbeknownst to most observers, these eye-catching photosynthetic pigments do more than provide aesthetic beauty to our lives. They are critical components in a biological protection system that prevents chlorophyll, the most essential plant pigment, from breaking down under high light stress. In a way that is not yet fully understood, xanthophylls are able to be converted from one form into another and back again in the so-called "Xanthophyll cycle." The molecular components of this cycle appear to be capable of harmlessly deactivating excess excited state energy before it catalyzes the destruction of chlorophyll. Interestingly, the same components may also regulate the flow of absorbed solar energy between photosynthetic proteins. This research will investigate precisely how the protection and flow regulation are accomplished. Protein preparations from several higher plant and algal systems will be systematically investigated. A combination of biochemical, molecular biological, and spectroscopic tools will be used. The overall goal of the research is to elucidate the molecular details of how the Xanthophyll cycle works. A better understanding of how plants convert solar energy into chemical energy and withstand stress under bright solar conditions is expected to be obtained from this work.

光合作用生物具有保护机制，通过该机制，在过量的光能导致光合作用机构的光破坏之前被消散。此外，从光收集色素-蛋白质复合物到光合反应中心的能量流动受到高度调节。控制这些过程的分子特征尚不清楚。叶黄素色素参与了这一机制，但其参与的确切性质尚不清楚。在这个项目中，几种不同的叶黄素将被研究。要进行的实验包括稳态和时间分辨吸收和荧光光谱和电化学测定。光谱实验将测量叶黄素和叶绿素之间能量转移的效率和动力学。电化学实验将揭示分子在溶液中的氧化电位和结合在色素蛋白复合物中的氧化电位。本研究的主要目的是研究在非辐射能量耗散中被认为是重要的每一个分子因素，以揭示其在体内发生的详细分子机制。要探索的因素包括叶黄素的组成、聚集状态、pH、磷酸化、能级的位置和色素的氧化电位。将探讨叶黄素作为叶绿素荧光的直接或间接猝灭剂的参与问题。关于叶黄素通过能量转移或电子转移机制猝灭叶绿素荧光的假设将被验证。这些实验对于扩大我们对光合生物如何保护自己免受过度的光能吸收和对不同环境条件作出反应，同时保持生存所必需的有效能量流的看法很重要。任何观察过新英格兰秋叶鲜艳的橙色和黄色的人都对叶黄素很熟悉。然而，大多数观察者都不知道，这些引人注目的光合色素不仅仅为我们的生活提供美感。它们是生物保护系统的关键组成部分，可以防止叶绿素（最重要的植物色素）在强光胁迫下分解。在所谓的“叶黄素循环”中，叶黄素能够从一种形式转化为另一种形式，并以一种尚未完全理解的方式再次转化。这个循环的分子成分似乎能够无害地使多余的激发态能量失活，然后再催化叶绿素的破坏。有趣的是，同样的成分也可能调节光合蛋白之间吸收的太阳能的流动。本研究将精确地探讨保护和流量调节是如何完成的。将系统地研究几种高等植物和藻类系统的蛋白质制备。将使用生物化学、分子生物学和光谱工具的组合。这项研究的总体目标是阐明叶黄素循环如何起作用的分子细节。这项工作有望更好地了解植物如何将太阳能转化为化学能并在明亮的太阳条件下承受压力。