title: ΔpH-dependent non-photochemical quenching (qE) of excited chlorophylls in the photosystem II core complex of the freshwater cyanobacterium Synechococcus sp PCC 7942.
abstract: Light-induced and lumen acidity-dependent quenching (qE) of excited chlorophylls (Chl) in vivo has been amply documented in plants and algae, but not in cyanobacteria, using primarily the saturation pulse method of quenching analysis which is applied to continuously illuminated samples. This method is unsuitable for cyanobacteria because the background illumination elicits in them a very large Chl a fluorescence signal, due to a state 2 to state 1 transition, which masks fluorescence changes due to other causes. We investigated the qE problem in the cyanobacterium Synechococcus sp. PCC 7942 using a kinetic method (Chl a fluorescence induction) with which qE can be examined before the onset of the state 2 to state 1 transition and the attendant rise of Chl a fluorescence. Our results confirm the existence of a qE mechanism that operates on excited Chls a in Photosystem II core complexes of cyanobacteria.
authors.affiliation: Institute of Biosciences and Applications, National Center for Scientific Research Demokritos, Aghia Paraskevi Attikis 15310, Greece. Electronic address: kstam@bio.demokritos.gr.
authors.forename: Kostas
authors.initials: K
authors.lastname: Stamatakis
authors.affiliation: Institute of Biosciences and Applications, National Center for Scientific Research Demokritos, Aghia Paraskevi Attikis 15310, Greece.
authors.forename: George C
authors.initials: GC
authors.lastname: Papageorgiou
mesh_terms: D002734:Chlorophyll / Q000378:metabolism*; D000077194:Chlorophyll A; D004579:Electron Transport; D004735:Energy Transfer; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D046940:Synechococcus / Q000378:metabolism* / Q000528:radiation effects; D013997:Time Factors
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D000077194:Chlorophyll A
keywords: Chlorophyll a FI; Cyanobacteria; PS decay; qE; ΔpH