Excitation energy transfer to Photosystem I in filaments and heterocysts of Nostoc punctiforme
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
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.
heterocyst, photosystem I, energy transfer, excitation, Nosotc punctiforme, phycobilisome, photosystem II
Biochemistry and Molecular Biology
Research subject Biochemistry
IdentifiersURN: urn:nbn:se:uu:diva-108463DOI: 10.1016/j.bbabio.2009.12.014ISI: 000274772900010PubMedID: 20036211OAI: oai:DiVA.org:uu-108463DiVA: diva2:235949