title: PMS: photosystem I electron donor or fluorescence quencher.
abstract: Light energy harvested by the pigments in Photosystem I (PSI) is used for charge separation in the reaction center (RC), after which the positive charge resides on a special chlorophyll dimer called P700. In studies on the PSI trapping kinetics, P700(+) is usually chemically reduced to re-open the RCs. So far, the information available about the reduction rate and possible chlorophyll fluorescence quenching effects of these reducing agents is limited. This information is indispensible to estimate the fraction of open RCs under known experimental conditions. Moreover, it would be important to understand if these reagents have a chlorophyll fluorescence quenching effects to avoid the introduction of exogenous singlet excitation quenching in the measurements. In this study, we investigated the effect of the commonly used reducing agent phenazine methosulfate (PMS) on the RC and fluorescence emission of higher plant PSI-LHCI. We measured the P700(+) reduction rate for different PMS concentrations, and show that we can give a reliable estimation on the fraction of closed RCs based on these rates. The data show that PMS is quenching chlorophyll fluorescence emission. Finally, we determined that the fluorescence quantum yield of PSI with closed RCs is 4% higher than if the RCs are open.
authors: Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands. ewientjes@hotmail.com
authors: Emilie
authors: E
authors: Wientjes
authors: Roberta
authors: R
authors: Croce
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry* / Q000378:metabolism; D004583:Electrons; D005453:Fluorescence; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D008773:Methylphenazonium Methosulfate / Q000494:pharmacology*; D010084:Oxidation-Reduction; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D020524:Thylakoids / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D002734:Chlorophyll; D008773:Methylphenazonium Methosulfate; C001785:chlorophyll P 700