Uphill energy transfer in photosystem I from Chlamydomonas reinhardtii. Time-resolved fluorescence measurements at 77 K

Wojciech Giera*, Sebastian Szewczyk, Michael D. McConnell, Kevin E. Redding, Rienk van Grondelle, Krzysztof Gibasiewicz

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Energetic properties of chlorophylls in photosynthetic complexes are strongly modulated by their interaction with the protein matrix and by inter-pigment coupling. This spectral tuning is especially striking in photosystem I (PSI) complexes that contain low-energy chlorophylls emitting above 700 nm. Such low-energy chlorophylls have been observed in cyanobacterial PSI, algal and plant PSI–LHCI complexes, and individual light-harvesting complex I (LHCI) proteins. However, there has been no direct evidence of their presence in algal PSI core complexes lacking LHCI. In order to determine the lowest-energy states of chlorophylls and their dynamics in algal PSI antenna systems, we performed time-resolved fluorescence measurements at 77 K for PSI core and PSI–LHCI complexes isolated from the green alga Chlamydomonas reinhardtii. The pool of low-energy chlorophylls observed in PSI cores is generally smaller and less red-shifted than that observed in PSI–LHCI complexes. Excitation energy equilibration between bulk and low-energy chlorophylls in the PSI–LHCI complexes at 77 K leads to population of excited states that are less red-shifted (by ~ 12 nm) than at room temperature. On the other hand, analysis of the detection wavelength dependence of the effective trapping time of bulk excitations in the PSI core at 77 K provided evidence for an energy threshold at ~ 675 nm, above which trapping slows down. Based on these observations, we postulate that excitation energy transfer from bulk to low-energy chlorophylls and from bulk to reaction center chlorophylls are thermally activated uphill processes that likely occur via higher excitonic states of energy accepting chlorophylls.

Original languageEnglish
Pages (from-to)1-15
Number of pages15
JournalPhotosynthesis Research
Volume137
Issue number2
DOIs
Publication statusPublished - 4 Apr 2018

Funding

The research leading to these results has received funding from LASERLAB-EUROPE II: Grant Agreement No. 228334. R.v.G. acknowledges financial support from VU University Amsterdam, the Laserlab-Europe Consortium, the TOP Grant (700.58.305) from the Foundation of Chemical Sciences part of NWO, the advanced investigator Grant (267333, PHOTPROT) from the European Research Council, the EU FP7 Project PAPETS (GA 323901). R.v.G. gratefully acknowledges his Academy Professor grant from the Netherlands Royal Academy of Sciences (KNAW). K.R. acknowledges support from the U.S. National Science Foundation (Grant MCB-1052573). K.G. gratefully acknowledges financial support from the Polish government (Scientific Project No. N N202 085440). Acknowledgements The research leading to these results has received funding from LASERLAB-EUROPE II: Grant Agreement No. 228334. R.v.G. acknowledges financial support from VU University Amsterdam, the Laserlab-Europe Consortium, the TOP Grant (700.58.305) from the Foundation of Chemical Sciences part of NWO, the advanced investigator Grant (267333, PHOTPROT) from the European Research Council, the EU FP7 Project PAPETS (GA 323901). R.v.G. gratefully acknowledges his Academy Professor grant from the Netherlands Royal Academy of Sciences (KNAW). K.R. acknowledges support from the U.S. National Science Foundation (Grant MCB-1052573). K.G. gratefully acknowledges financial support from the Polish government (Scientific Project No. N N202 085440).

FundersFunder number
EU FP7GA 323901
Laserlab-Europe Consortium700.58.305
Netherlands Royal Academy of Sciences
PHOTPROT
Polish governmentN N202 085440
U.S. National Science FoundationMCB-1052573
Seventh Framework Programme267333
European Research Council
Koninklijke Nederlandse Akademie van Wetenschappen
Vrije Universiteit Amsterdam
Nederlandse Organisatie voor Wetenschappelijk Onderzoek

    Keywords

    • Chlamydomonas reinhardtii
    • Excitation energy transfer
    • Light-harvesting complex I
    • Photosystem I
    • Red chlorophylls
    • Time-resolved fluorescence

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