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  • 1
    ISSN: 1432-0983
    Keywords: Plastome ; cpDNA variability ; Dasycladaceae ; Restriction fragment length polymorphism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cells from Acetabularia mediterranea and Batophora oerstedii have been cloned and several lines established from these clones. Chloroplast DNA (cpDNA) was isolated from these lines and characterized by restriction enzyme analysis. A high degree of restriction fragment length polymorphism was observed between the different lines of each species. This high intraspecific variability in the cpDNA arrangement was confirmed by hybridization to well-characterized chloroplast genes. Based on results obtained from DNA-denaturing experiments, a GC content of 49.9% and 51.7% was calculated for different lines of A. mediterranea and B. oerstedii, respectively. This is close to that found in the cyanobacteria.
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  • 2
    ISSN: 1615-6102
    Keywords: Acetabularia acetabulum ; Perinuclear microtubule formation ; Nucleolar morphology ; Meiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Microtubules (MT) are a feature of all eukaryotic cells. However, they have not been observed in the cytoplasm of the vegetative phase ofAcetabularia acetabulum. Previous investigators have reported that, in the propagative phase, MTs function as anchors in the transport of secondary nuclei to the cap. They also form elaborate arrays around nuclei during cyst formation. The life history ofA. acetabulum is marked by changes in chromatin, the nucleolus, and the perinuclear cytoplasm. In this study light microscopical features of the nucleolus and changes in chromatin, labelled with anti-histon antibodies, were used to define the developmental stages. Anti-tubulin antibodies have been used to trace the origin and development of MTs, MTs are formed on the surface of the primary nucleus. They are organized first into short thick “sticks” and then later elongate into thinner strands which enclose the nucleus in a dense network. Following these events on the surface of the nucleus, the spindle develops inside the nuclear membrane which remains intact throughout the mitotic division.
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  • 3
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Actively transcribed DNA was made visible in nuclear material from the giant unicellular green alga Batophora oerstedii (Chlorophyta, Dasycladaceae) by means of Miller's spreading technique. A conspicuous feature of a major part of the spread material is that actively transcribed regions are adjacent to each other resulting either in a lack of, or at least in extremely short spacer DNA. The length and the localization of these repetitive transcriptional units in the nucleolar material indicate that they are rRNA cistrons. In addition to the spacer-free DNA, repetitious structures have been found within the nucleolar material of individual nucleic, in which spacers occur. The transcriptional units in the spacer-free regions appear to have the same length as the transcriptional units separated by spacers.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 64 (1967), S. 1-12 
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Incorporation of precursors of RNA into the enucleated cells ofAcetabularia mediterranea andPolyphysa cliftonii has been studied under conditions which exclude the possibility of errors due to contamination of the preparations by nuclei, nuclear debris or microorganisms. Radioactive RNA has been isolated from the chloroplast, mitochondrial and supernatant cytoplasm fractions of nucleated and enucleated cells. Sucrose density gradient centrifugation of the isolated labelled RNA produces a sedimentation profile of radioactivity which is similar to that of RNA isolated fromE. coli ribosomes. Anion exchange chromatography of alkaline hydrolysates of the 23 s and 16 s ribosomal RNA fractions shows incorporation of labelled uracil into RNA in the form of 2′(3′)-UMP and 2′(3′)-CMP. Labelled guanosine is incorporated only as 2′(3′)-GMP. A slowly sedimenting radioactivity peak has been chromatographed on a Hershey column and found to correspond to cold t-RNA.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 64 (1967), S. 13-25 
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary RNA-synthesis by isolated chloroplasts fromAcetabularia mediterranea andPolyphysa cliftonii has been studied under conditions which exclude the possibility of errors due to contamination of the preparations by nuclei, nuclear fragments or microorganisms. Radioactive RNA isolated from chloroplasts has a sucrose density gradient sedimentation profile with peaks near 23 s, 16 s, 9 s, and 4 s. The 23 s and 16 s peaks were identified as ribosomal RNA. The 4 s component is considered to be t-RNA. The nature of the 9 s-peak is unknown. Incorporation of RNA precursors is inhibited by darkness, actinomycin and DNase. The incorporation of any one of the 5'-nucleoside triphosphates of RNA was shown to occur independently of the presence of the other three nucleoside triphosphates in the medium. These results have been taken as further evidence of the presence of an endogenous pool of nucleoside triphosphates within the chloroplasts. Anion exchange chromatography of alkaline hydrolysates of the newly synthesized RNA has shown that the precursors are incorporated into the four 2'(3')-nucleoside monophosphates of RNA. The significance of these findings to the question of autonomy of chloroplasts has been discussed. It has been concluded that the amount of template DNA available in the chloroplasts is not sufficient to support a complete genetic autonomy of the chloroplasts.
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  • 6
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 7
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An electron microscopic survey of nuclear events and changes in the perinuclear cytoplasm during the generative phase ofAcetabularia is presented with details on late stages in the maturation of the primary nucleus, possible modes of formation of secondary nuclei, the mitosis of secondary nuclei, migration of secondary nuclei into the stalk and the cap, the fine structure of nuclei and perinuclear cytoplasm during cyst formation and gametogenesis as well as during gamete fusion and zygote formation.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 155 (1990), S. 19-28 
    ISSN: 1615-6102
    Keywords: Acetabularia ; Karyotype ; Meiosis ; Pachytene ; Primary nucleus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Meiotic and mitotic divisions of the nuclei ofAcetabularia mediterranea were studied with the aid of DAPI fluorochrome and fluorescence microscopy. We report, for the first time, the formation of 20 bivalents in the primary nucleus during the early stages of meiosis. The karyotype of 20 chromosomes in the secondary nuclei is described. The nucleoli are reduced and finally fuse to form a small sphere as the primary nucleus undergoes a first meiotic division. Three of the 20 bivalents at pachytene are clearly attached to the nucleolus. Immediately after meiosis, the haploid nuclei undergo a succession of mitoses from which the karyotype was worked out. The haploid complement consists of 20 chromosomes. Four of the chromosomes have median, 10 have submedian and 6 have subterminal constrictions. Secondary constrictions were detected in 3 long and 2 intermediate chromosomes as well as in 1 short chromosome. The karyotype and the pairing behavior point to the possible allopolyploid nature of the alga.
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  • 9
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Active cistrons and non-transcribed spacers of rDNA were made visible in spread preparations of nucleolar material from different species of the green alga family Dasycladaceae (Chlorophyta). The data observed show a difference in length in transcribed rDNA regions between Acetabularia peniculus Solms-Laubach, Acetabularia dentata Solms-Laubach on the one hand and Acetabularia ryukyuensis Okamura et Yamada, Dasycladus clavaeformis J. Agardh, Cymopolia van bosseae Solms-Laubach and Batophora oerstedii J. Agardh on the other: The large size difference between spacer intercepts of different species is very conspicuous. While the Acetabularia species have long non-transcribed spacers they are very short or even not observable in the other Dasycladaceen species studied. Peculiarities found in rDNA include extra long spacers between cistrons, single extra long cistrons together with rDNA cistrons on the same strand and rDNA-sized cistrons alternately arranged on one strand with larger sized cistrons. In spite of extensive searching, inversions were never found in spread nucleolar material. However, they were frequent in spread material of whole nuclei.
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  • 10
    ISSN: 1432-2048
    Keywords: Acetabularia ; Acyl lipid formation ; Chloroplast (fatty-acid synthesis) ; Fatty acid (synthesis) ; Prenyl lipid formation ; Mevalonate pathway
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A gentle procedure allowed the isolation of intact and highly active chloroplasts from the unicellular green algaAcetabularia mediterranea. These chloroplasts incorporated carbon from NaH14CO3 into fatty acids and prenyl lipids at a rate of about 20–50 nmol carbon· (mg chlorophyll)−1·h−1. Most of the fatty acids formed in vitro were esterified in galactolipids. The main prenyl lipids synthesized were the chlorophyll side chain, intermediates of the carotenogenic path, α-and β-carotene, as well as lutein. Large amounts of [1-14C]acetate were incorporated, but exclusively into fatty acids.Isopentenyl diphosphate was a good substrate for prenyl-lipid formation in hypotonically treated chloroplasts. The envelope of intact chloroplasts, however, was impermeable to this compound. Intermediates of the mevalonate pathway were not accepted as precursors under conditions whereisopentenyl diphosphate was well incorporated. The results show that the lipid biosynthetic pathways in the plastids ofAcetabularia, a member of the ancient family of Dasycladaceae, are very similar to those in higher-plant plastids.
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