Etude de la dynamique des populations de cilies d'un torrent experimental pendant deux annees

The sampling of Ciliates performed in a little experimental torrent through two years, showed a great similarity of the two annual cycles. This similarity concerns both the species composition as well as the dynamics of the Ciliates populations. The basic species which affect the community structure are as follows: Ctedoctema acanthocrypta, Mesodinium acarus, Cyclidium glaucoma, Cinetochilum margaritaceum, Pleuronema coronatum, Lacrymaria pupula, Aspidisca costata and Holosticha vernalis. The dynamics of the ciliated Protozoa living in this environment seem to be influenced by the speed of the current, the temperature and the amount of dissolved organic matter in the water.

---

Etude de la dynamique des populations de cilies d'un torrent experimental pendant deux annees

     

The role of soluble cytochrome c-551 in cyclic electron flow-driven active transport in Chromatium vinosum

Spheroplasts have been prepared from the photosynthetic purple sulfur bacterium Chromatium vinosum by lysozyme plus ethylenediaminetetraacetic acid treatment. These spheroplasts are able to take up alanine in the light, but light-dependent alanine uptake is lost upon subsequent washing of the spheroplasts. The observations that alanine uptake driven by a potassium plus valinomycin-induced membrane potential (outside positive) is not affected by washing and that light-dependent alanine uptake can be restored by addition of the supernatant from washing suggest that a soluble electron carrier is lost during washing. Light-dependent alanine uptake in washed spheroplasts could be restored by addition of C. vinosum cytochrome c-551. Other soluble electron carriers from C. vinosum (high-potential iron protein, cytochrome ‘f’, cytochrome c′ and the flavocytochrome c-552) did not restore alanine uptake nor did a variety of other soluble electron carrier proteins from other organisms. These results suggest that cytochrome c-551 functions as an electron carrier in the cyclic electron transfer chain of C. vinosum. Mitochondrial cytochrome c (equine heart) and cytochrome c-551 from Pseudomonas aeruginosa were highly effective in restoring light-dependent alanine uptake in washed spheroplasts, making it likely that C. vinosum cytochrome c-551 is related by evolution to the same cytochrome c family as these other two c cytochromes.     

Photosensory transduction in Euglena gracilis: Effect of some metabolic drugs on the photophobic response

We have investigated the effect of some metabolic drugs, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 2,4-dinitrophenol (DNP), sodium azide (NaN₃), on the photobehavior of single cells of Euglena gracilis, in order to clarify the relevance of different metabolic pathways in the process of photoperception and sensory transduction in this alga. The results obtained show that the photophobic response of Euglena is not affected by the action of these drugs. This suggests that neither the photosynthetic process nor oxidative phosphorylation play a significant role in the phenomenon of photosensory transduction in Euglena.List of Abbreviations DNP 2,4-dinitrophenol - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PSI Photosystem I - PSII Photosystem II     

Nuclear protein synthesis in regenerating rat liver : Selective histone inhibition by α-amanitin

Nuclear protein synthesis has been studied in regenerating rat hepatocytes after partial hepatectomy and α-amanitin treatment. The toxin induced a marked and precocious inhibition of histone synthesis without affecting the acidic nuclear proteins. This inhibition preceded the inhibition of DNA synthesis. The modification of polyribosome profile and of [¹⁴C]lysine incorporation on synthesized polypeptides were consistent with a reduction of specific mRNAs.     

DNA synthesis and nuclear division during formation of infection structures by bean rust uredospore germlings

Plectonema boryanum can grow in the dark with ribose, sucrose, mannitol, maltose, glucose, or fructose. Cell doubling times with 10 mM substrate are the following: 5 days with ribose, 6 days with sucrose or mannitol, 10 days with maltose, 12 days with glucose, and 13 days with fructose; with ribose plus 0.1% casamino acids it is 2.5 days. Dark-grown cells appear morphologically similar to light-grown cells. Cells grown in the dark for several years remain pigmented and resume photoautotrophic growth when placed in the light. Dim light (85 lux) increases the growth rate with ribose and with ribose plus casamino acids to nearlytwice that of the dark rate. In moderate light, growth takes place with ribose even in the presence of 1x10^-5 M DCMU.