Cryo-imaging of photosystems and phycobilisomes in Anabaena sp. PCC 7120 cells.
Primary photosynthetic reactions take place inside thylakoid membrane where light-to-chemical energy conversion is catalyzed by two pigment-protein complexes, photosystem I (PSI) and photosystem II (PSII). Light absorption in cyanobacteria is increased by pigment-protein supercomplexes--phycobilisomes (PBSs) situated on thylakoid membrane surfaces that transfer excitation energy into both photosystems. We have explored the localization of PSI, PSII and PBSs in thylakoid membrane of native cyanobacteria cell Anabaena sp. 7120 by means of cryogenic confocal microscopy. We have adapted a conventional temperature controlling stage to an Olympus FV1000 confocal microscope. The presence of red shifted emission of chlorophylls from PSI has been confirmed by spectral measurements. Confocal fluorescence images of PSI (in a spectral range 710-750 nm), PSII (in a spectral range 690-705 nm) and PBSs (in a spectral range 650-680 nm) were recorded at low temperature. Co-localization of images showed spatial heterogeneity of PSI, PSII and PBSs over the thylakoid membrane, and three dominant areas were identified: PSI-PSII-PBS supercomplex area, PSII-PBS supercomplex area and PSI area. The observed results were discussed with regard to light-harvesting regulation in cyanobacteria.
Institute of Microbiology, CAS, Centrum Algatech, Třeboň, Czech Republic. Electronic address: steinbach@alga.cz.
Gábor
G
Steinbach
Department of Mineralogy, Geochemistry and Petrology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary. Electronic address: schubert@geo.u-szeged.hu.
Félix
F
Schubert
Institute of Microbiology, CAS, Centrum Algatech, Třeboň, Czech Republic; Faculty of Science, Institute of Chemistry and Biochemistry, University of South Bohemia, Branišovská 31, 370 05 České Budějovice, Czech Republic. Electronic address: kana@alga.cz.
Radek
R
Kaňa
D017033:Anabaena / Q000166:cytology* / Q000201:enzymology* / Q000378:metabolism; D018613:Microscopy, Confocal; D008958:Models, Molecular; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D045524:Phycobilisomes / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D021381:Protein Transport
D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes
Confocal microscopy; Cryogenic microscopy; Cyanobacteria; Membrane domains; Photosynthesis