MORPHOGENESIS OF PHOTOSYNTHETIC APPARATUS IN RHODOSPIRILLUM RUBRUM .2. KINETICS OF CHROMATOPHORE (THYLAKOID) SYNTHESIS BY MEMBRANES LABELED WITH [2-14C]ACETATE

1. 1. The participation of the cytoplasmic membrane in chromatophore (thylakoid) morphogenesis was examined in Rhodospirillum rubrum. 2. 2. Membrane fractions were labeled preferentially by incorporation of [2-14C]-acetate into phospholipids. 3. 3. Anaerobic cultures were grown under moderate light intensity (4000 lux) and then transferred to low light intensity (400 lux). This caused bacteriochlorophyll synthesis to start immediately. However, the total protein content of the culture was not changed during the first 3 to 4 h of incubation. 4. 4. Before lowering the light intensity the cytoplasmic membrane was labeled more rapidly by [2-14C]acetate than were the chromatophores (thylakoids). 5. 5. After lowering the light intensity, even though there was no measurable growth, the rate of incorporation of radioactivity into the chromatophores (thylakoids) was equal to the rate of bacteriochlorophyll synthesis. 6. 6. During pulse-chase experiments under low-light conditions there was a shift in the distribution of radioactivity between the cytoplasmic membrane and the chromatophores (thylakoids). Whereas the radioactivity in the chromatophores increased, the radioactivity in the cytoplasmic membrane decreased. 7. 7. The possibility is discussed that the chromatophores and the cytoplasmic membrane form a continuous membrane system in which the chromatophores represent the modified cytoplasmic membrane. © 1969.