Excitation energy transfer from phycobiliprotein to chlorophyll d in intact cells of Acaryochloris marina studied by time- and wavelength-resolved fluorescence spectroscopy

Abstract

The fluorescence decay spectra and the excitation energy transfer from the phycobiliproteins (PBP) to the chlorophyll-antennae of intact cells of the chlorophyll (Chl) d-dominated cyanobacterium Acaryochloris marina were investigated at 298 and 77 K by time- and wavelength-correlated single photon counting fluorescence spectroscopy. At 298 K it was found that (i) the fluorescence dynamics in A. marina is characterized by two emission peaks located at about 650 and 725 nm, (ii) the intensity of the 650 nm fluorescence depends strongly on the excitation wavelength, being high upon excitation of phycobiliprotein (PBP) at 632 nm but virtually absent upon excitation of chlorophyll at 430 nm, (iii) the 650 nm fluorescence band decayed predominantly with a lifetime of 70 +/- 20 ps, (iv) the 725 nm fluorescence, which was observed independent of the excitation wavelength, can be described by a three-exponential decay kinetics with lifetimes depending on the open or the closed state (F(0) or F(m)) of the reaction centre of Photosystem II (PS II). Based on the results of this study, it is inferred that the excitation energy transfer from phycobiliproteins to Chl d of PS II in A. marina occurs with a time constant of about 70 ps, which is about three times faster than the energy transfer from the phycobilisomes to PS II in the Chl a-containing cyanobacterium Synechococcus 6301. A similar fast PBP to Chl d excitation energy transfer was also observed at 77 K. At 77 K a small long-lived fluorescence decay component with a lifetime of 14 ns was observed in the 640-700 nm spectral range. However, it has a rather featureless spectrum, not typical for Chl a, and was only observed upon excitation at 400 nm but not upon excitation at 632 and 654 nm. Thus, this long-lived fluorescence component cannot be used as an indicator that the primary PS II donor of Acaryochloris marina contains Chl a.

Wide-field photon counting fluorescence lifetime imaging microscopy: application to photosynthesizing systems

“…1 with common values of lifetimes (linked parameters) and cell-dependent pre-exponential factors a i . In good agreement with ensemble measurements of A. marina (Petrášek et al 2005), the fluorescence decay in the ten cells is characterized by two main components with lifetimes of s fast = 60 ps and s middle = 800 ps and a very slow component with a lifetime of about s slow = 1.6 ns. The preexponential factors for two cells are shown in the table inserted in Fig.…”

“…Although their applications to imaging may be limited, since only one line within the sample can be imaged, the DL detectors combined with polychromators are particularly suitable for spectrally resolved fluorescence decay analysis (Bergmann et al 1998). The DL detector has been applied to the investigation of time-and spectrally resolved fluorescence of photosynthetic fluorophores in the cyanobacterium A. marina (Petrášek et al 2005). Currently, two-dimensional DL detectors, with the two delay lines oriented perpendicularly to each other, are being developed (Czasch et al 2007b;Michalet et al 2006).…”

“…Acaryochloris marina also has a phycobiliprotein antenna containing phycocyanin (PC) and allophycocyanin (APC), which increase light-harvesting efficiency by filling the spectral gap between the blue and red absorption bands of the chlorophylls (560-670 nm) (Hu et al 1999;Marquardt et al 1997). Therefore, the fluorescence spectrum of A. marina is characterized by two bands at about 650 nm (PBP emission) and 725 nm (Chl d emission) (Hu et al 1999;Petrášek et al 2005). According to ensemble measurements, the 650 nm fluorescence decays predominantly with a lifetime of about 70 ps which reflects a fast energy transfer from APC to Chl d. In contrast, the 725 nm fluorescence exhibits a three-exponential decay kinetics with lifetimes of about 100 ps, 600 ps, and 1.5 ns which are ascribed to Chl d of PS I (100 ps component) and PS II with open (600 ps component) and closed (1.5 ns) reaction centers (Petrášek et al, 2005).…”

“…The 60 ps decay component is assigned to Chl d fluorescence from PS I (Mimuro et al 1999;Petrášek et al 2005). The other two decay components originate from Chl d of PS II.…”

“…Therefore, the fluorescence spectrum of A. marina is characterized by two bands at about 650 nm (PBP emission) and 725 nm (Chl d emission) (Hu et al 1999;Petrášek et al 2005). According to ensemble measurements, the 650 nm fluorescence decays predominantly with a lifetime of about 70 ps which reflects a fast energy transfer from APC to Chl d. In contrast, the 725 nm fluorescence exhibits a three-exponential decay kinetics with lifetimes of about 100 ps, 600 ps, and 1.5 ns which are ascribed to Chl d of PS I (100 ps component) and PS II with open (600 ps component) and closed (1.5 ns) reaction centers (Petrášek et al, 2005). In order to obtain information about the fluorescence dynamics in individual cells, measurements were performed by using the wide-field FLIM setup described above.…”