Energy transfer and trapping in Synechococcus WH 7803

Abstract

Excitation energy transfer (EET) and trapping in Synechococcus WH 7803 whole cells and isolated photosystem I (PSI) complexes have been studied by time-resolved emission spectroscopy at room temperature (RT) and at 77 K. With the help of global and target analysis, the pathways of EET and the charge separation dynamics have been identified. Energy absorbed in the phycobilisome (PB) rods by the abundant phycoerythrin (PE) is funneled to phycocyanin (PC645) and from there to the core that contains allophycocyanin (APC660 and APC680). Intra-PB EET rates have been estimated to range from 11 to 68/ns. It was estimated that at RT, the terminal emitter of the phycobilisome, APC680, transfers its energy at a rate of 90/ns to PSI and at a rate of 50/ns to PSII. At 77 K, the redshifted Chl a states in the PSI core were heterogeneous, with maximum emission at 697 and 707 nm. In 72% of the PSI complexes, the bulk Chl a in equilibrium with F697 decayed with a main trapping lifetime of 39 ps.Electronic supplementary materialThe online version of this article (doi:10.1007/s11120-017-0451-2) contains supplementary material, which is available to authorized users.

Time-resolved fluorescence study of excitation energy transfer in the cyanobacterium Anabaena PCC 7120

“…The time-resolved fluorescence kinetics of intact Anabaena filaments share a lot of similarities with the reported kinetics from cells of different cyanobacterial strains (Mullineaux and Holzwarth 1991;Tian et al 2011;Acuña et al 2018b). Upon direct excitation of the PBS rods, the fluorescence kinetics in a few hundred picoseconds reflects primarily EET within the PBS, which is apparent by the similar DAES observed in cells and isolated PBS.…”

“…An elaborated functional compartmental model of EET in Synechocystis PCC 6803 has been recently reported (van Stokkum et al 2018), according to which the slowest EET rates are between the core cylinders (115-145 ps) and between the rods and the core (68-115 ps). By time-resolved fluorescence, Acuña et al (2018b) reported a 20 ps EET time from the PBS terminal emitter to PSII, i.e. faster than the EET within the PBS.…”

Modelling excitation energy transfer and trapping in the filamentous cyanobacterium Anabaena variabilis PCC 7120

“…The overall trapping of the excitation energy in PSI core occurs typically in 12-60 ps in cyanobacterial organisms and higher plants depending on the antenna size and the amount of red Chls (Croce et al 2000;Wientjes et al 2011;van Stokkum et al 2013;Akhtar et al 2018;Gobets et al 2001). The estimated PSI trapping observed in our model is ≈18 ps which is comparable with the previously observed lifetimes of ≈16 and ≈ 2 ps in Synechocystis and Synechococcus (Tian et al 2011;Acuna et al 2018a). The 18 ps PSI trapping seems to be a plausible average decay time considering the small amount of red Chl in a pool of ≈100 bulk Chls (cf.…”

“…Megacomplex 1 involves PBS-PSII-PSI as PBS is well known to feed energy to both PSs, i.e. PBS coupled to both PSI and PSII (Liu et al 2013;Acuna et al 2018a;Tian et al 2011). PSII is known to be best described with a core which is in equilibrium with a non-radiative radical pair (RP) (Tian et al 2013).…”

“…PBS is connected to the membrane via a multidomain core-membrane linker, L CM (Tang et al 2015). Ultra-fast time-resolved spectroscopy measurements have been used to probe the rates of EET from PBS to photosystems (PSs) in cyanobacteria such as Synechocystis (Tian et al 2011) and Synechococcus (Acuna et al 2018a). The efficiency of light energy transferred from PBS to the chlorophylls (Chls) in PSI and PSII approaches 100% (Glazer 1984).…”