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Excitation energy transfer to Photosystem I in filaments and heterocysts of Nostoc punctiforme
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
2010 (English)In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1797, no 3, 425-433 p.Article in journal (Refereed) Published
Abstract [en]

Cyanobacteria adapt to varying light conditions by controlling the amount of excitation energy to the photosystems. On the minute time scale this leads to redirection of the excitation energy, usually referred to as state transitions, which involves movement of the phycobilisomes. We have studied short-term light adaptation in isolated heterocysts and intact filaments from the cyanobacterium Nostoc punctiforme ATCC 29133. In N. punctiforme vegetative cells differentiate into heterocysts where nitrogen fixation takes place. Photosystem II is inactivated in the heterocysts, and the abundancy of Photosystem I is increased relative to the vegetative cells. To study light-induced changes in energy transfer to Photosystem I, pre-illumination was made to dark adapted isolated heterocysts. Illumination wavelengths were chosen to excite Photosystem I (708 nm) or phycobilisomes (560. nm) specifically. In heterocysts that were pre-illuminated at 708. nm, fluorescence from the phycobilisome terminal emitter was observed in the 77 K emission spectrum. However, illumination with 560. nm light caused quenching of the emission from the terminal emitter, with a simultaneous increase in the emission at 750 nm, indicating that the 560 nm pre-illumination caused trimerization of Photosystem I. Excitation spectra showed that 560 nm pre-illumination led to an increase in excitation transfer from the phycobilisomes to trimeric Photosystem I. Illumination at 708 nm did not lead to increased energy transfer from the phycobilisome to Photosystem I compared to dark adapted samples. The measurements were repeated using intact filaments containing vegetative cells, and found to give very similar results as the heterocysts. This demonstrates that molecular events leading to increased excitation energy transfer to Photosystem I, including trimerization, are independent of Photosystem II activity.

Place, publisher, year, edition, pages
2010. Vol. 1797, no 3, 425-433 p.
Keyword [en]
heterocyst, photosystem I, energy transfer, excitation, Nosotc punctiforme, phycobilisome, photosystem II
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:uu:diva-108463DOI: 10.1016/j.bbabio.2009.12.014ISI: 000274772900010PubMedID: 20036211OAI: oai:DiVA.org:uu-108463DiVA: diva2:235949
Available from: 2012-05-08 Created: 2009-09-18 Last updated: 2017-12-13Bibliographically approved
In thesis
1. The Heterocysts of Nostoc punctiforme: From Proteomics to Energy Transfer
Open this publication in new window or tab >>The Heterocysts of Nostoc punctiforme: From Proteomics to Energy Transfer
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis is to provide a thorough characterization of the photosynthetic machinery from the heterocysts of Nostoc punctiforme strain ATCC 29133. In this thesis I describe the protocols I have optimized for the isolation of thylakoids from vegetative cells, the purification of heterocysts and the isolation of thylakoids from the purified heterocysts. The composition of the thylakoid membranes was studied by two dimensional electrophoresis and mass-spectrometry. Further insight into the functionality of the photosynthetic complexes was obtained by EPR, electron transport measurements through Photosystem II (PSII), and fluorescence spectroscopy. The proteome of the heterocysts thylakoids compared to that of the vegetative cell was found to be dominated by Photosystem I (PSI) and ATP-synthase complexes, both essential for keeping high nitrogenase activities. Surprisingly, we found a significant amount of assembled monomeric PSII complexes in the heterocysts thylakoid membranes. We measured in vitro light-driven electron transfer from PSII in heterocysts using an artificial electron donor, suggesting that under certain circumstances heterocysts might activate PSII. Parallel to my main research I also worked in a collaboration to elucidate the total proteome of Nostoc sp. strain 7120 and Nostoc punctiforme using quantitative shotgun proteomics. Several hundred proteins were quantified for both species. It was possible to trace the detailed changes that occurred in the energy and nitrogen metabolism of a heterocyst after differentiation. Moreover, the presence of PSII proteins identified in our membrane proteome was also confirmed and extended. Lastly, I studied how the heterocysts are capable of responding to variations in light quality as compared to vegetative cells. Using 77 K fluorescence spectroscopy on heterocysts and vegetative cells previously illuminated with light at specific wavelengths, I was able to demonstrate that heterocysts still possess a possibly modified but functional antenna system, capable of harvesting light and transferring energy preferentially to PSI. The characterization of the membrane and total proteome permitted to draw a more comprehensive and integrated picture of the interplay between the distinct metabolic processes that are carried out in each cell type at the same time; from oxygenic photosynthesis and carbon fixation in the vegetative cells to the anoxygenic cyclic photophosphorylation essential to power nitrogen assimilation in the heterocysts.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 78 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 671
Keyword
Nostoc punctiforme, heterocyst, photosynthesis, thylakoid, isolation, proteomics, photosystem, energy transfer, hydrogen
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:uu:diva-108413 (URN)978-91-554-7607-6 (ISBN)
Public defence
2009-10-30, Häggsalen, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2009-10-09 Created: 2009-09-17 Last updated: 2009-10-09

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Cardona, TanaiMagnuson, Ann

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