In this paper we propose an energy dissipation mechanism that is completely reliant on changes in the aggregation state of the phycobilisome light-harvesting antenna components. All photosynthetic organisms regulate the efficiency of excitation energy transfer (EET) to fit light energy supply to biochemical demands. Not many do this to the extent required of desert crust cyanobacteria. Following predawn dew deposition, they harvest light energy with maximum efficiency until desiccating in the early morning hours. In the desiccated state, absorbed energy is completely quenched. Time and spectrally resolved fluorescence emission measurements of the desiccated desert crust Leptolyngbya ohadii strain identified (i) reduced EET between phycobilisome components, (ii) shorter fluorescence lifetimes, and (iii) red shift in the emission spectra, compared with the hydrated state. These changes coincide with a loss of the ordered phycobilisome structure, evident from small-angle neutron and X-ray scattering and cryo-transmission electron microscopy data. Based on these observations we propose a model where in the hydrated state the organized rod structure of the phycobilisome supports directional EET to reaction centers with minimal losses due to thermal dissipation. In the desiccated state this structure is lost, giving way to more random aggregates. The resulting EET path will exhibit increased coupling to the environment and enhanced quenching.
|Original language||American English|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - 29 Aug 2017|
Bibliographical noteFunding Information:
ACKNOWLEDGMENTS. We gratefully acknowledge SANS beamtime at Heinz Maier-Leibnitz Zentrum. This work was supported by the joint Israeli Indian Grant (ISF-UGC 2733/16) (to N.K.) and by the grant from the Israel and Taiwan Ministries of Science, Technology and Space (to N.K. and Y.P.). R.R.C. was supported by BioSolar Cells, cofinanced by the Dutch Ministry of Economic Affairs and the Foundation for Fundamental Research on Matter, part of The Netherlands Organization for Scientific Research (Project 10TBSC24-3). G.G. and M.D. were supported by the National Research Development and Innovation Office of Hungary (OTKA K 112688 and GINOP-2.3.2-15-2016-00058 and PD 121243).
© 2017, National Academy of Sciences. All rights reserved.
- Energy dissipation
- Photosynthetic efficiency