Investigation of the excited states dynamics in the Chl d- containing cyanobacterium Acaryochloris marina by time- and wavelength correlated single-photon counting

摘要

The phototrophic cyanobacterium Acaryochloris marina discovered in 1996 has a unique composition of the light harvesting system. The chlorophyll (Chl) antenna contains mainly Chl d instead of the usually dominant Chl a and the Phycobiliprotein (PBP) antenna has a simpler rod shaped structure than in typical cynobacteria.rnThe interaction of the photosynthetic subunits and especially the mechanisms regulating the energy transfer under different stress conditions are presently interesting and open fields in photosynthesis research.rnIn this study we use time- and wavelength-resolved single photon counting to investigate the excited states dynamics in living cells of A. marina. The fluorescence dynamics is synchronistically monitored in the visible and near infrared spectrum with high signal to noise ratio and short data acquisition times while using low excitation light intensities. These attributes are necessary to investigate photosynthetic processes in sensitive biological samples, when the light emission varies due to metabolic changes.rnThe results suggest a fast excitation energy transfer kinetics of 20-30 ps along the PBP antenna of A.marina followed by a transfer of about 60 ps to the Chl d antenna.rnCells of A. marina which are stored at 0℃ for some time show a decoupling of the PBP antenna, which is partially reversible when the sample is kept at 25℃ for a short time. Decoupling effects appearing after strong illumination with white light (1600 W/m~2) suggest a mechanism which removes the PBP antenna at different stress conditions to avoid photo damage of the reaction center of Photosystem II (PS II).