Energy transfer processes in Gloeobacter violaceus PCC 7421 that possesses phycobilisomes with a unique morphology

Abstract

We examined energy transfer dynamics in phycobilisomes (PBSs) of cyanobacteria in relation to the morphology and pigment compositions of PBSs. We used Gloeobacter violaceus PCC 7421 and measured time-resolved fluorescence spectra in three types of samples, i.e., intact cells, PBSs, and rod assemblies separated from cores. Fremyella diplosiphon, a cyanobacterial species well known for its complementary chromatic adaptation, was used for comparison after growing under red or green light. Spectral data were analyzed by the fluorescence decay-associated spectra with components common in lifetimes with a time resolution of 3 ps/channel and a spectral resolution of 2 nm/channel. This ensured a higher resolution of the energy transfer kinetics than those obtained by global analysis with fewer sampling intervals. We resolved four spectral components in phycoerythrin (PE), three in phycocyanin (PC), two in allophycocyanin, and two in photosystem II. The bundle-like PBSs of G. violaceus showed multiple energy transfer pathways; fast ( approximately 10 ps) and slow ( approximately 100 ps and approximately 500 ps) pathways were found in rods consisting of PE and PC. Energy transfer time from PE to PC was two times slower in G. violaceus than in F. diplosiphon grown under green light.

Spectral properties of the CP43-deletion mutant of Synechocystis sp. PCC 6803

“…Therefore it is reasonable to assume that PS I Chl a fluorescence overlapped the observed 720-nm band. There were two vibrational bands from allophycocyanin or the terminal pigment of PBS at 753 and 772 nm (Szalontai et al 1989;Yokono et al 2008). The excitation spectra monitored at 685 and 695 nm showed no contribution of Chl a to these two bands (Fig.…”

“…Upon excitation at 600 nm, the PS I Chl a band shifted to 725 nm and its intensity became lower than that of the 685-nm band, indicating that PS I fluorescence became weak. Two bands observed at 753 and 772 nm were assigned to vibrational bands of phycobiliproteins (Szalontai et al 1989;Yokono et al 2008), indicating that the main 686-nm band probably arose from phycobiliproteins. This origin was demonstrated by the excitation spectrum (Fig.…”

“…Upon excitation at 600 nm, a clear peak was observed at 686 nm with five small bands at 656, 666, 722, 751, and 772 nm. The former two came from phycocyanin and allophycocyanin, respectively, and the latter two were vibrational bands of phycobiliproteins (Szalontai et al 1989;Yokono et al 2008). Thus, the 686-nm band mainly came from phycobiliproteins.…”

Regulation of excitation energy transfer in diatom PSII dimer: How does it change the destination of excitation energy?

“…Spectral data were measured at 77 K with 1-nm intervals. Following a global analysis of the fluorescence kinetics, the fluorescence decay-associated spectra (FDAS) were constructed using the method reported previously [9,34]. In brief, fluorescence rise and decay curves were deconvoluted using free-running 5 exponential components with an instrument function.…”

Excitation energy relaxation in a symbiotic cyanobacterium, Prochloron didemni, occurring in coral-reef ascidians, and in a free-living cyanobacterium, Prochlorothrix hollandica

“…Time-resolved fluorescence spectra (TRFS) were measured with a time-correlated single-photon counting system at 77 K as described previously [18]. The excitation wavelength was 425 nm, at which all pigments (Chl a, Chl b and carotenoids) in Prochloron and Prochlorothrix were simultaneously excited.…”