Etude du developpement, de la structure et de l'ultrastructure de la racine de betterave a sucre par des examens en microscopie optique et electronique

Photosynthetic activity and organization of chlorophyll(Chl)-protein complexes in a temperature sensitive mutant of Chlorella pyrenoidosa have been investigated. The mutant is practically indistinguishable from wild type cells when grown at 25 C. However, mutant cells grown at 33 C do not synthesize Chl and lose their ability to evolve O(2). O(2) evolution and Chl synthesis are restored upon incubation of the 33 C grown cells at 25 C in absence of cell division (repair).Based on polarographic measurements of photosynthetic activities, variable fluorescence, 77 K fluorescence emission, excitation spectra, analysis of Chl-protein complexes, membrane polypeptide pattern and radioactive labeling using sodium dodecyl sulfate-polyacrylamide gel electrophoresis techniques during growth at 33 C and/or under repair conditions, it is concluded that: a, polypeptides of chloroplastic translation required for H(2)O-splitting activity are absent from membranes of 33 C grown cells. Their synthesis and/or assembly during the repair process is light-dependent. b, Polypeptides required for the formation of photosystem II and photosytem I reaction centers continue to be formed during growth at 33 C in absence of Chl synthesis. These can be assembled into functional units following Chl synthesis and energization of the membranes during the repair process. c, The Chl-protein complex serving as an antenna of photosystem I is disorganized, and the Chl is used for the formation of functional reaction centers of photosystem I during growth at 33 C.These results show that Chl-protein complexes can be dissociated in vivo and reassembled in a different way; and formation of Chl-protein complexes can occur stepwise from previously synthesized and newly formed components including both polypeptides and Chl.

1. In Scenedesmus acutus Tomaselli, endogenous variations in cell progeny production and chlorophyll formation have been found which are very similar to those previously described in Chlorella by Hesse (Z. Pflanzenphysiol. 67, 58-77, 1972). When the dark phase of the light-dark-cycle is prolonged to a certain extent, cell productivity drops to a minimal value during the next normal light-dark-cycle. If the duration of the supplementary dark treatment comes near to 24 h, cell productivity is almost normal during the next cycle. 2. Nucleic acid labeling with radioactive precursors is very similar in Scenedesmus acutus and Chlorella pyrenoidosa. Short time labeling with uridine results in labeled chloroplastic RNA and DNA, the cytoplasmic RNA being almost unlabeled. With guanosine, both chloroplastic and cytoplasmic RNA as well as DNA are labelled. In nucleic acid separation on acrylamide gels special caution must be taken, since endocellular RNases are particularely active in some cell stages of Scenedesmus. Optimal results are obtained with ripe mother cells; during nucleic acid purification, cell homogenates have to be frozen together with the phenol-cresol mixture. 3. Large differences in guanosine incorporation are found after treatment of the cells with supplementary dark time. After the normal 10:12 h light-dark-cycle, and also after 24 h of supplementarry dark time, much more radioactive guanosine is incorporated into chloroplastic RNA than into cytoplasmic RNA. After 12 h of supplementary dark time, however, cytoplasmic RNA is more extensively labeled than chloroplastic RNA. 4. When the specific radioactivity of guanosine is diluted to one half, the incorporation into the rRNA of cytoplasm and chloroplast is strongly reduced. This is due to the filling up of the guanosine pool in the two compartments. In contrast, DNA labeling is hardly influenced by reduced specific radioactivity of the precursor. This may be interpreted as meaning that the radioactive labeling reflects the rate of DNA synthesis rather than the size of the guanosine pool in the nucleus. Differences found in the labeling of DNA after 12 and 24 h of supplementary dark time can than be interpreted as variations in DNA synthesis rate.

The sequence of Chlorella cytoplasmic 5 S RNA has been determined by fingerprinting techniques. Partial digests were fractionated by a two-dimensional acrylamide gel electrophoretic technique, which indicates whether specific fragments are paired in the molecule. In this way, the four main base-paired regions of the molecule were located. The sequence of Chlorella cytoplasmic 5 S RNA is related to, but different from, that of other eukaryotic 5 S RNAs: it shows approximately 60% homology with vertebrate 5 S RNA and 40% homology with yeast 5 S RNA. In some respects the conformation of the molecule in solution is quite different from that of other sequenced 5 S RNAs: in particular, the highly accessible region found around position 40 in all other 5 S RNAs (prokaryotic and eukaryotic) does not exist in this molecule.

In , tritiated uridine is incorporated specifically into the RNA of the chloroplast. The 16 S and 23 S ribosomal RNA become labeled after at least 15 min. Short pulse labeling of 5 min results in peaks of radioactivity in the 17 S region and at the heavy side of the 23 S peak, as shown by polyacrylamide electrophoresis.During chase treatment with unlabeled uridine after the pulse labeling, a shift of radioactivity from the 17 S to the 16 S region is observed. At the same time, the radioactivity over the 23 S speak becomes symmetrical. In the 17 S region, there are at least two peaks which appear and disappear during chase treatment. From data of specific radioactivity a precursor—end product relation can be deduced.After blocking of the chloroplast translation with spectinomycin, the RNA in the 17 S region is accumulated. This product is not stringently the same as that from pulse labeling experiments, because it migrates slightly faster than 17 S RNA. Removal of the antibiotic results in a shift of the radioactivity to the 16 S region. At the same time, the previously blocked chloroplast ribosome synthesis is reinitiated.Attempts have been made to localize the precursor molecules of 17 S and 23 S within the cell. By means of differential centrifugation it has been shown that the precursor RNA components are located in ribosomal particles. No free precursor molecules are found in the ribosome-free supernatant. This is the case in normal as well as in spectinomycin-treated cells.The results are discussed in view of the possible role of chloroplast ribosomal particles as processing agents for the maturation of chloroplast ribosomal RNA.

Uridine incorporation into chloroplastic ribosomes of Chlorella pyrenoiuosa (strain 211/8b. has been investigated during synchronous cell culture. Ribosomes can be labeleu with uridine throughout the uevelopmental cycle. Most of the radioactivity of the ribosomal fraction is found in the subunits of the chloroplast ribosomes which sediment with 50 Sand 30 S, respectively. The intensity of uridine incorporation varies during the cell cycle. Maximal incorporation is found uuring the dark period of the 14: 10 hrs light-dark-cycle. Uridine incorporation is enhanced by the light in young autospores as well as in older cells at the end of the light period. A slight inhibition by the light, however, is observed in the first parts of the light period and of the dark period. The incorporation patterns of uridine into the ribosomal fractions are not modified by the light.

FEBS LettersVolume 37, Issue 2 p. 333-334 Full-length articleFree Access Nucleotide sequence ofChlorella cytoplasmic 5 S RNA First published: December 01, 1973 https://doi.org/10.1016/0014-5793(73)80490-9Citations: 10AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. References [1] Sankoff D., Cedergren R.J., J. Mol. Biol., 77, (1973), 159– 164. [2] Galling G., Jordan B.R., Biochimie, 54, (1972), 1257– 1265. [3] Brownlee G.C., Sanger F., Barrell B.G., J. Mol. Biol., 34, (1968), 379– 412. [4] Ehresmann C., Stiegler P., Fellner P., Ebel J.P., Biochimie, 53, (1972), 901– 967. [5] Vigne R., Jordan B.R., Biochimie, 53, (1971), 981– 986. [6] Litt M., Biochemistry, 8, (1969), 3249– 3253. [7] Bellemare G., Jordan B.R., Rocca-Serra J., Monier R., Biochimie, 54, (1972), 1453– 1466. [8] Forget B.G., Weissman S.M., Science, 158, (1967), 1695– 1699. [9] Hindley J., Page S.M., FEBS Letters, 26, (1972), 157– 160. Citing Literature Volume37, Issue2December 01, 1973Pages 333-334 ReferencesRelatedInformation