title: Characterization of wave phenomena in the relaxation of flash-induced chlorophyll fluorescence yield in cyanobacteria.
abstract: Fluorescence yield relaxation following a light pulse was studied in various cyanobacteria under aerobic and microaerobic conditions. In Synechocystis PCC 6803 fluorescence yield decays in a monotonous fashion under aerobic conditions. However, under microaerobic conditions the decay exhibits a wave feature showing a dip at 30-50 ms after the flash followed by a transient rise, reaching maximum at ~1s, before decaying back to the initial level. The wave phenomenon can also be observed under aerobic conditions in cells preilluminated with continuous light. Illumination preconditions cells for the wave phenomenon transiently: for few seconds in Synechocystis PCC 6803, but up to one hour in Thermosynechocystis elongatus BP-1. The wave is eliminated by inhibition of plastoquinone binding either to the QB site of Photosystem-II or the Qo site of cytochrome b6f complex by 3-(3',4'-dichlorophenyl)-1,1-dimethylurea or 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, respectively. The wave is also absent in mutants, which lack either Photosystem-I or the NAD(P)H-quinone oxidoreductase (NDH-1) complex. Monitoring the redox state of the plastoquinone pool revealed that the dip of the fluorescence wave corresponds to transient oxidation, whereas the following rise to re-reduction of the plastoquinone pool. It is concluded that the unusual wave feature of fluorescence yield relaxation reflects transient oxidation of highly reduced plastoquinone pool by Photosystem-I followed by its re-reduction from stromal components via the NDH-1 complex, which is transmitted back to the fluorescence yield modulator primary quinone electron acceptor via charge equilibria. Potential applications of the wave phenomenon in studying photosynthetic and respiratory electron transport are discussed. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy.
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvari krt. 62, 6726 Szeged, Hungary.
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Deák
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvari krt. 62, 6726 Szeged, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Sass
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvari krt. 62, 6726 Szeged, Hungary.
authors.forename: Eva
authors.initials: E
authors.lastname: Kiss
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Temesvari krt. 62, 6726 Szeged, Hungary. Electronic address: vass.imre@brc.mta.hu.
authors.forename: Imre
authors.initials: I
authors.lastname: Vass
mesh_terms: D002734:Chlorophyll / Q000737:chemistry*; D000458:Cyanobacteria / Q000378:metabolism*; D004579:Electron Transport; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000502:physiology; D045332:Photosystem II Protein Complex / Q000737:chemistry; D010971:Plastoquinone / Q000737:chemistry; D046939:Synechocystis / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D016660:NAD(P)H Dehydrogenase (Quinone); D010971:Plastoquinone
keywords: Cyclic electron transport; Linear electron transport; NDH-1 complex; Photosystem II; Variable Chl fluorescence