Title |
Uphill energy transfer in photosystem I from Chlamydomonas reinhardtii. Time-resolved fluorescence measurements at 77 K
|
---|---|
Published in |
Photosynthesis Research, April 2018
|
DOI | 10.1007/s11120-018-0506-z |
Pubmed ID | |
Authors |
Wojciech Giera, Sebastian Szewczyk, Michael D. McConnell, Kevin E. Redding, Rienk van Grondelle, Krzysztof Gibasiewicz |
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. |
Mendeley readers
Geographical breakdown
Country | Count | As % |
---|---|---|
Unknown | 33 | 100% |
Demographic breakdown
Readers by professional status | Count | As % |
---|---|---|
Student > Ph. D. Student | 11 | 33% |
Researcher | 4 | 12% |
Professor | 4 | 12% |
Student > Master | 3 | 9% |
Student > Doctoral Student | 2 | 6% |
Other | 5 | 15% |
Unknown | 4 | 12% |
Readers by discipline | Count | As % |
---|---|---|
Biochemistry, Genetics and Molecular Biology | 8 | 24% |
Agricultural and Biological Sciences | 6 | 18% |
Chemistry | 6 | 18% |
Physics and Astronomy | 4 | 12% |
Materials Science | 1 | 3% |
Other | 0 | 0% |
Unknown | 8 | 24% |