Probing the picosecond kinetics of the photosystem II core complex in vivo

Abstract

Photosystems I (PSI) and II (PSII) are two major pigment-protein complexes of photosynthetic organisms that function in series to convert sunlight energy into chemical energy. We have studied the picosecond fluorescence behaviour of the core of both photosystems in vivo by using two Synechocystis PCC 6803 mutants: BE cells contain PSI but are lacking both PSII and the light-harvesting complexes called phycobilisomes (PBs) whereas PAL cells contain both PSI and PSII but lack the PBs. Measurements were performed at room temperature and at 77 K. The fluorescence kinetics of PSI and PSII can nicely be separated, en passant providing the PSI/PSII ratio. At room temperature, the PSI kinetics are identical to those of isolated PSI whereas the PSII kinetics can equally well be described by the in vitro trap-limited model of Y. Miloslavina, M. Szczepaniak, M. G. Muller, J. Sander, M. Nowaczyk, M. Rogner and A. R. Holzwarth, Biophys J., 2009, 96(2), 621-631, and by the transfer-to-the-trap-limited model of C. D. van der Weij-de Wit, J. P. Dekker, R. van Grondelle and I. H. M. van Stokkum, J. Phys. Chem. A, 2011, 115(16), 3947-3956, albeit that the in vivo kinetics turn out to be somewhat slower. At 77 K several low-energy pigments are observed in both photosystems which complicate the overall dynamics but the PSII kinetics can still be described by both a trap-limited and a transfer-to-the-trap-limited model.

Systems biophysics: Global and target analysis of light harvesting and photochemical quenching in vivo

“…We then estimate a stoichiometry of 1.74 or 1.83 PSII dimer per PSI trimer for the samples with PSIIRC in the open or closed condition, respectively. When expressed as the ratio of PSIRC to PSIIRC, this corresponds to 0.86 or 0.82, which is in agreement with the values reported by Stadnichuk et al (2009) of 0.7 ± 0.2 and 0.76 (Krumova et al 2010;Tian et al 2013).…”

“…Since it is not possible to resolve the small contributions of the faster equilibration lifetimes (<10 ps), no attempt is made to resolve the equilibration within the B2 compartment between the PSIIRC and the CP43 and CP47 antenna complexes, which is still disputed (Barter et al 2001;Miloslavina et al 2006;Raszewski and Renger 2008;van der Weij−de Wit et al 2011;Tian et al 2013).…”

“…They can be mutated, which allows us to study the properties of subsystems in vivo. In particular, the BE and PAL mutant of Synechocystis (Ajlani and Vernotte 1998;Krumova et al 2010;Tian et al 2013) can be considered elementary photosynthetic systems. They lack the phycobilisome antenna.…”

Cyanobacterial flv4-2 Operon-Encoded Proteins Optimize Light Harvesting and Charge Separation in Photosystem II

“…The energy transfer and charge separation kinetics in isolated PSII core particles and PSII cores in vivo have been well studied with timeresolved fluorescence and transient absorption measurements. Dominant lifetime components with open reaction centers (RCs; oxidized Q A ) were observed in the range from 35-40 ps (Miloslavina et al, 2006) to 60-80 ps (Schatz et al, 1987;Tian et al, 2013) and around z300-500 ps. The first component reflects excitation trapping/primary charge separation in PSII core complexes containing only the antenna complexes CP43 and CP47, while the second has been assigned to secondary electron transfer to the quinone acceptor Q A together with recombination (van der Weij-de Wit et al, 2011;Tian et al, 2013).…”

“…Dominant lifetime components with open reaction centers (RCs; oxidized Q A ) were observed in the range from 35-40 ps (Miloslavina et al, 2006) to 60-80 ps (Schatz et al, 1987;Tian et al, 2013) and around z300-500 ps. The first component reflects excitation trapping/primary charge separation in PSII core complexes containing only the antenna complexes CP43 and CP47, while the second has been assigned to secondary electron transfer to the quinone acceptor Q A together with recombination (van der Weij-de Wit et al, 2011;Tian et al, 2013). The kinetics of PSII with closed RCs (Q A reduced) in both isolated cores and intact organisms have been studied by a number of groups (Roelofs et al, 1992;Szczepaniak et al, 2009;Tian et al, 2013).…”