Relationships between chloroplast cytoplasmic rRNA accumulation during the cell cycle of the green alga Scenedesmus quadricauda (original) (raw)

The patterns of accumulation of chloroplast and cytoplasmic ribosomal RNA (chl-and cyt-rRNA) were followed in synchronous cultures of the green alga Scenedesmus quadricauda (Turp.) Bréb. Heterotrophic growth conditions and/ar specific inhibitors of protein and rRNA synthesis in chloroplast were used as tools for studying the relationships between these two processes. Heterotrophically grown cells showed the same pattern of accumulation of both chl-and cyt-rRNA as in photoautotrophically grown cultures. Similarly the ratio of chl-/cyt-rRNA was maintained at 0.2. This suggests that light had a trophic function in regulating the synthesis of both rRNA species. The presence of rifampicin during cell division in the dark inhibited the accumulation of chl-rRNA in newly released daughter cells. while the accumulation of cyt-rRNA was not affected. Consequently. the ratio of chl-/cyt-rRNA dropped to 0.1, whereas the same value in untreated darkened daughters increased to 0.4. After washing aut the rifampicin or illuminating the culture, the rates of accumulation of both rRNAs varied in both cultures bot the chl-/cyt-rRNA ratios tended to equilibrate at 0.2 which is characteristic for continuously illuminated cells. The presence of chloramphenicol in heterotrophic cultures caused a complete inhibition of protein. rRNA and DNA synthesis in chloroplast bot the cells .were able to complete at least two cell cycles. When cells in the light and dark were treated with chloramphenicol in the presence of glucose, no differences in the cell cycle and growth were found. These results indicate that concomitant growth. protein synthesis and the accumulation of rRNA in chloroplast are not required for the progress of the algal cell cycle. The synthesis of starch in heterotrophically grown cells with chloramphenicol was the same as in the control heterotrophically growri eDItore. It therefore seems to be the only chloroplast function required for maintaining the algal cell cycle.

Sign up for access to the world's latest research.

checkGet notified about relevant papers

checkSave papers to use in your research

checkJoin the discussion with peers

checkTrack your impact