Near-infrared action spectra of fluorescence, cytochrome oxidation and shift in carotenoid absorption in purple bacteria

• 1.

  1. Action spectra for bacteriochlorophyll fluorescence were measured for a number of species of purple bacteria. For a few species action spectra for light-induced absorbance changes (light-induced cytochrome oxidation and shift in carotenoid absorption) were also measured, and were found to be similar to the action spectra for fluorescence.

• 2.

  2. In a number of species, e.g. Chromatium and Rhodopseudomonas spheroides, the action spectra were different from the absorption spectra, indicating that the efficiency of the transfer of excitation energy to the longest-wavelength form of bacteriochlorophyll may be lower than 100% for some types of bacteriochlorophyll. This applied e.g. to the bacteriochlorophyll types absorping at about 800 mμ and 850 mμ in Chromatium and Rps. spheroides, respectively. A possible explanation is that these bacteriochlorophyll types exist in 2 different pools, with different efficiencies of energy transfer to fluorescent B 890.

• 3.

  3. In Rhodopseudomonas palustris light quanta absorbed absorbed at 800 mμ were more active than quanta absorbed at about 890 mμ in exciting bacteriochlorophyll fluorescence. This may be explained by assuming 2 pools of the bacteriochlorophyll type absorbing around 890 mμ, with different fluorescence yields.