PATHS OF DEACTIVATION OF EXCITED BACTERIOCHLOROPHYLL-C IN THE GREEN PHOTOSYNTHETIC BACTERIUM PROSTHECOCHLORIS-AESTUARII

Absorption, fluorescence, delayed emission and photoacoustic spectra w ere obtained for the green photosynthetic bacterium. Whole cells incor porated in fluid (culture medium, viscous solution of polyvinyl alcoho l, glycol) and rigid (isotropic and stretched polyvinyl alcohol film) media were investigated. The polarized absorption spectra of the stret ched polyvinyl alcohol sample showed that the Q(y) transition moments of chlorosomal bacteriochlorophyll c was almost parallel to the film a xis. Bacteriochlorophyll (BChl) c degradation occurred in some of the samples during prolonged storage and as a result a pigment absorbing a t 670 nm, which was disaggregated BChl c or/and bacteriopheophytin c, was formed. This pigment was unoriented in stretched polyvinyl alcohol . The fluorescence spectrum of native cells can be analyzed using thre e Gaussian components at 754, 781 and 813 nm. The first component seem s to be related to BChl c aggregates and the others to BChl a complexe s. The time-resolved delayed luminescence spectra showed that practica lly ah the complexes of green bacteria exhibited delayed emission but the decay times and intensities were different for the different compl exes. In the photoacoustic spectra two maxima of the chlorosomal BChl c forms were well resolved and located at 748 and 765 nm. The photoaco ustic maximum at 830 nm was probably related to the reaction centre (R C). In the Soret band the largest peak of the photoacoustic spectra wa s observed at 473 nn which showed that carotenoids absorbing in this r ange were losing more excitation by heat. The BChl c aggregates attach ed to chlorosome rods exhibited a peak at 446 nm. The efficient therma l deactivation also showed a BChl a located in RC (peak at 846 nn) and long-wavelength BChl a antenna complexes with a deactivation peak at 884 nn.