Photosynthetic membrane development in Rhodopseudomonas spheroides: Incorporation of bacteriochlorophyll and development of energy transfer and photochemical activity

Abstract

1. 1. Bleached cells of Rhodopseudomonas spheroides, obtained by aerobic growth in the light, rapidly synthesize bacteriochlororphyll and carotenoids when transferred to 4% oxygen in the dark. Fluorescence excitation spectra of whole cells during the initial stages of pigment synthesis indicate that the major fraction of the newly synthesized bacteriochlorophyll is immediately incorporated into photosynthetic membranes and can receive excitation energy transferred from the carotenoids. Activity of the photosynthetic reaction centers, as measured by the effect of dithionite addition on the fluorescence of the incorporated bacteriochlorophyll, develops simultaneously with pigment incorporation. 2. 2. Fluorescence excitation and emission spectra also indicate the presence of an unbound form of bacteriochlorophyll in vivo as well as a form of bacteriopheophytin. We suggest that this free bacteriochlorophyll is in a “pool” from which it is incorporated into the membranes and that the bacteriopheophytin (or bacteriopheophorbide) is formed by the degradation of the free and thus unprotected form of the bacteriochlorophyll.