title: Origin of pronounced differences in 77 K fluorescence of the green alga Chlamydomonas reinhardtii in state 1 and 2.
abstract: In response to changes in the reduction state of the plastoquinone pool in its thylakoid membrane, the green alga Chlamydomonas reinhardtti is performing state transitions: remodelling of its thylakoid membrane leads to a redistribution of excitations over photosystems I and II (PSI and PSII). These transitions are accompanied by marked changes in the 77 K fluorescence spectrum, which form the accepted signature of state transitions. The changes are generally thought to reflect a redistribution of light-harvesting complexes (LHCs) over PSII (fluorescing below 700 nm) and PSI (fluorescing above 700 nm). Here we studied the picosecond fluorescence properties of C. reinhardtti over a broad range of wavelengths with very low excitation intensities (0.2 nJ per laser pulse). Cells were directly used for time-resolved fluorescence measurements at 77 K without further treatment, such as medium exchange with glycerol. It is observed that upon going from state 1 (relatively more fluorescence below 700 nm) to state 2 (relatively more fluorescence above 700 nm), a large part of the fluorescence of LHC/PSII becomes substantially quenched in concurrence with LHC detachment from PSII, whereas the absolute amount of PSI fluorescence hardly changes. These results are in agreement with the recent proposal that the amount of LHC moving from PSII to PSI upon going from state 1 to state 2 is rather limited (Unlu et al. Proc Natl Acad Sci USA 111 (9):3460-3465, 2014).
authors.affiliation: Laboratory of Biophysics, Wageningen University, Dreijenlaan 3, 6703 HA, Wageningen, The Netherlands.
authors.forename: Caner
authors.initials: C
authors.lastname: Ünlü
authors.affiliation: Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1105, 1081 HV, Amsterdam, The Netherlands.
authors.forename: Iryna
authors.initials: I
authors.lastname: Polukhina
authors.affiliation: Laboratory of Biophysics, Wageningen University, Dreijenlaan 3, 6703 HA, Wageningen, The Netherlands. herbert.vanamerongen@wur.nl.|MicroSpectroscopy Centre, Wageningen University, 6703 HA, Wageningen, The Netherlands. herbert.vanamerongen@wur.nl.
authors.forename: Herbert
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000378:metabolism; D005453:Fluorescence; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000528:radiation effects*
chemical_list: D045342:Light-Harvesting Protein Complexes
keywords: Excitation energy transfer; Fluorescence quenching; Light harvesting; Photosystem; State transitions; Time-resolved fluorescence spectroscopy