Reaction centres (RC) from the purpie bacterium Rhodohacter sphaeroides (strain R-24.1 and carotenoid-free mutant R-26.1) were separated and immobilized in isotropic and stretched polyvinyl alcohol (PVA) films. Absorption, fluorescence, delayed luminescence (8-300 K) and photoacoustic spectra (PAS) of immobilized samples were measured. The RC from wild strain R-24.1 and ffom carotenoid-free mutant R-26.1 were differently oriented in the stretched polymer film. In R-24.1 the long axis of the RC complex was directed under some angle with respect to the perpendicular direction to the PVA film plane, whereas in R-26.1 it was almost perpendicular to this plane. The shapes of linear dichroism (LD) of both strains were different. Delayed luminescence (DL) bands were located in a similar wavelength range as the bacteriochlorophyll and bacteriopheophytin prompt fluorescence bands. Intensity of DL was independent of temperature in the 8-300 K range. The intensity of DL was about three time lower than that of the fluorescence. The dependence of PAS on the frequency of radiation modulation and on the phase shift between modulated acting radiation and measured PAS showed that part of the thermal deactivation was undergoing slowly. Intensity ratio of the slow component to the fast one and/or decay time of the slow component of thermal deactivation were different for various chromophores and for RC ffom the two strains of bacteria.
Etiolated leaves of three different species, maize, wheat, and pea, as well as a pea mutant (lip1) were used to compare the excitation spectra of protochlorophyllide (Pchlide) in the red region. The species used have different composition of short-wavelength and long-wavelength Pchlide forms. The relation between different forms was furthermore changed through incubating the leaves in 5-aminolevulinic acid (ALA), which caused an accumulation of short-wavelength Pchlide forms, as shown by changes in absorption and fluorescence spectra. This is the first time a comprehensive comparison is made between excitation spectra from different species covering an emission wavelength range of 675-750 nm using fluorescence equipment with electronic compensation for the variations in excitation irradiance. The different forms of Pchlide having excitations peaks at 628, 632, 637, 650, and 672 nm could be best measured at 675, 700, 710, 725, and 750 nm, respectively. Measuring emission at wavelengths between 675-710 nm gave an exaggeration of the short-wavelength forms and measuring at longer wavelengths gave for the pea leaves an exaggeration of the 672 nm peak. In general, an energy transfer from short-wavelength Pchlide forms to long-wavelength Pchlide forms occurred, but such an energy transfer sometimes seemed to be limited as a result of a discrete location of the Pchlide spectral forms. The excitation spectra resembling the absorption spectrum most were measured at an emission wavelength of 740 nm. Measuring the excitation at 710 nm gave higher intensity of the spectra but the short-wavelength forms were accentuated. and M. R. Amirjani, C. Sundqvist.