TEMPERATURE-DEPENDENCE OF PICOSECOND FLUORESCENCE KINETICS OF A CYANOBACTERIAL PHOTOSYSTEM-I PARTICLE

Picosecond time-resolved fluorescence of photosystem I particles isolated from Synechococcus sp. was recorded in the wavelength range from 680 nm to 736 nm for temperatures of 6-degrees-C to 42-degrees-C and -100-degrees-C using the single-photon-timing technique. By global analysis of the data we found four contributing lifetime components at the higher temperatures (tau1 almost-equal-to 12 ps, tau2 almost-equal-to 35 ps, tau3 almost-equal-to 65 ps, tau4 almost-equal-to 1000 ps). We attribute tau1 to an energy transfer between two pigment pools, tau2 to the charge separation process in the reaction center, component tau3 is assigned to aggregate and tau4 to uncoupled chlorophyll emission. The corresponding decay-associated spectra are presented. We also applied a target analysis procedure to fit parameters of a kinetic model directly to the data. The resulting rate constants and species-associated spectra are discussed. The data indicate substantial spectral heterogeneity in the antenna with at least three substantially different chlorophyll pools. The overall exciton decay kinetics (by charge separation) is trap-limited.