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

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Photosynthetic 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 light-harvesting pigment-protein complexes to the photosynthetic reaction center is highly regulated. The controlling features of these processes are not well understood. Xanthophyll pigments have been implicated in the mechanisms, but the precise nature of their involvement is unclear. In order to address this issue steady state absorption, fluorescence, two-photon excitation, and time-resolved absorption and fluorescence spectroscopic experiments will be performed. These experiments will probe the energies and electronic configurations of the excited states of the xanthophylls and measure the efficiencies and dynamics of energy transfer between the xanthophylls and chlorophylls. Also, electrochemical analyses will be done to examine the oxidation potentials of the molecules. The xanthophylls to be studied differ in their structures, extents of pi-electron conjugation, excited state energies and oxidation potentials. This research will investigate precisely how energy dissipation and energy flow regulation are accomplished through a systematic study of these molecules in native, recombinant, and reconstituted pigment-protein complexes isolated from higher plants and algae. The major objective of this study is to examine each of the molecular factors thought to be important in these processes in order to reveal the detailed mechanisms by which they take place in vivo. This work is expected to lead to a better understanding of how plants convert solar energy into chemical energy and withstand stress under excess solar energy conditions.The broader impacts of this study include having the participating students obtain experience in the techniques for the isolation, purification and characterization of biological materials and in sophisticated optical spectroscopic methodologies. Part of their training will include writing papers and making presentations at scientific meetings at which the results of the studies will be openly disseminated. This project also involves the participation of a faculty member from an undergraduate institution. His direct involvement in the project would expand his research horizons and will have an impact on the science education at a liberal arts undergraduate institution.