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Defining the Far-Red Limit of Photosystem II in Spinach
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
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2009 (English)In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 21, no 8, 2391-2401 p.Article in journal (Refereed) Published
Abstract [en]

The far-red limit of photosystem II (PSII) photochemistry was studied in PSII-enriched membranes and PSII core preparations from spinach (Spinacia oleracea) after application of laser flashes between 730 and 820 nm. Light up to 800 nm was found to drive PSII activity in both acceptor side reduction and oxidation of the water-oxidizing CaMn4 cluster. Far-red illumination induced enhancement of, and slowed down decay kinetics of, variable fluorescence. Both effects reflect reduction of the acceptor side of PSII. The effects on the donor side of PSII were monitored using electron paramagnetic resonance spectroscopy. Signals from the S-2-, S-3-, and S-0-states could be detected after one, two, and three far-red flashes, respectively, indicating that PSII underwent conventional S-state transitions. Full PSII turnover was demonstrated by far-red flash-induced oxygen release, with oxygen appearing on the third flash. In addition, both the pheophytin anion and the Tyr Z radical were formed by far-red flashes. The efficiency of this far-red photochemistry in PSII decreases with increasing wavelength. The upper limit for detectable photochemistry in PSII on a single flash was determined to be 780 nm. In photoaccumulation experiments, photochemistry was detectable up to 800 nm. Implications for the energetics and energy levels of the charge separated states in PSII are discussed in light of the presented results.

Place, publisher, year, edition, pages
Rockville, Md: the American Society of Plant Biologists , 2009. Vol. 21, no 8, 2391-2401 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-127486DOI: 10.1105/tpc.108.064154ISI: 000270416700017OAI: oai:DiVA.org:uu-127486DiVA: diva2:330309
Available from: 2010-07-15 Created: 2010-07-13 Last updated: 2017-12-12Bibliographically approved
In thesis
1. The Far-Red Limit of Photosynthesis
Open this publication in new window or tab >>The Far-Red Limit of Photosynthesis
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The photosynthetic process has the unique ability to capture energy from sunlight and accumulate that energy in sugars and starch. This thesis deals with the light driven part of photosynthesis. The aim has been to investigate how the light-absorbing protein complexes Photosystem I (PS I) and Photosystem II (PS II), react upon illumination of light with lower energy (far-red light; 700-850 nm) than the absorption peak at respective primary donor, P700 and P680.  The results were unexpected. At 295 K, we showed that both PS I and PS II were able to perform photochemistry with light up to 130 nm above its respective primary donor absorption maxima. As such, it was found that the primary donors’ action spectra extended approximately 80 nm further out into the red-region of the spectrum than previously reported.  The ability to perform photochemistry with far-red light was conserved at cryogenic temperatures (< 77 K) in both photosystems. By performing EPR measurements on various photosystem preparations, under different illumination conditions the origin of the effect was localized to their respective reaction center. It is also likely that underlying mechanism is analogous for PS I and PS II, given the similarities in spatial coordination of the reaction center pigments. For PS II, the results obtained allowed us to suggest a model involving a previously unknown electron transfer pathway. This model is based upon the conclusion that the primary cation from primary charge separation induced by far-red light resides primarily on ChlD1 in P680. This is in contrast to the cation being located on PD1, as has been suggested as for visible light illumination.

The property to drive photochemistry with far-red wavelengths implies a hither to unknown absorption band, probably originating from the pigments that compose P700 and P680. The results presented here might clarify how the pigments inside P680 are coupled and also how the complex charge separation processes within the first picoseconds that initiate photosynthetic reactions occur.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 77 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1108
Keyword
Far-red light, Photosystem I, Photosystem II, P700, P680, EPR, Charge Separation
National Category
Natural Sciences Other Chemistry Topics
Research subject
Chemistry with specialization in Molecular Biomimetics
Identifiers
urn:nbn:se:uu:diva-213659 (URN)978-91-554-8835-2 (ISBN)
Public defence
2014-02-07, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
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Available from: 2014-01-16 Created: 2014-01-02 Last updated: 2014-01-24

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Thapper, AndersMamedov, FikretMokvist, FredrikHammarström, LeifStyring, Stenbjörn

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