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  • 1
    ISSN: 1432-1432
    Keywords: Key words: Gene families — Glutamine synthetase —Medicago truncatula— Phylogeny
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Glutamine synthetase type I (GSI) genes have previously been described only in prokaryotes except that the fungus Emericella nidulans contains a gene (fluG) which encodes a protein with a large N-terminal domain linked to a C-terminal GSI-like domain. Eukaryotes generally contain the type II (GSII) genes which have been shown to occur also in some prokaryotes. The question of whether GSI and GSII genes are orthologues or paralogues remains a point of controversy. In this article we show that GSI-like genes are widespread in higher plants and have characterized one of the genes from the legume Medicago truncatula. This gene is part of a small gene family and is expressed in many organs of the plant. It encodes a protein similar in size and with between 36 and 46% amino acid sequence similarity to prokaryotic GS proteins used in the analyses, whereas it is larger and with less than 25% similarity to GSII proteins, including those from the same plant species. Phylogenetic analyses suggest that this protein is most similar to putative proteins encoded by expressed sequence tags of other higher plant species (including dicots and a monocot) and forms a cluster with FluG as the most divergent of the GSI sequences. The discovery of GSI-like genes in higher plants supports the paralogous evolution of GSI and GSII genes, which has implications for the use of GS in molecular studies on evolution.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1432
    Keywords: Key words: Thioredoxins — Introns — Phylogeny
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. In contrast to prokaryotes, which typically possess one thioredoxin gene per genome, three different thioredoxin types have been described in higher plants. All are encoded by nuclear genes, but thioredoxins m and f are chloroplastic while thioredoxins h have no transit peptide and are probably cytoplasmic. We have cloned and sequenced Arabidopsis thaliana genomic fragments encoding the five previously described thioredoxins h, as well as a sixth gene encoding a new thioredoxin h. In spite of the high divergence of the sequences, five of them possess two introns at positions identical to the previously sequenced tobacco thioredoxin h gene, while a single one has only the first intron. The recently published sequence of Chlamydomonas thioredoxin h shows three introns, two at the same positions as in higher plants. This strongly suggests a common origin for all cytoplasmic thioredoxins of plants and green algae. In addition, we have cloned and sequenced pea DNA genomic fragments encoding thioredoxins m and f. The thioredoxin m sequence shows only one intron between the regions encoding the transit peptide and the mature protein, supporting the prokaryotic origin of this sequence and suggesting that its association with the transit peptide has been facilitated by exon shuffling. In contrast, the thioredoxin f sequence shows two introns, one at the same position as an intron in various plant and animal thioredoxins and the second at the same position as an intron in thioredoxin domains of disulfide isomerases. This strongly supports the hypothesis of a eukaryotic origin for chloroplastic thioredoxin f.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 103 (1998), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Flax (Linum usitatissimum) hypocotyl protoplasts immobilized in a calcium-alginate matrix give rise to embryo-like structures. A direct correlation was established between the presence of a set of ionically-bound cell wall proteins, which includes the basic polypeptides P184 and P183 with an apparent molecular mass of 25 kDa, and this morphogenic response. Microsequencing of tryptic fragments from P184 and P183 indicated homologies with the chitinase family. These homologies were confirmed by demonstrating that, after renaturation, such proteins express a potential chitinase activity in SDS-PAGE gel containing glycol chitin as synthetic substrate. Using degenerate primers from P184 internal sequences, we isolated one partial genomic sequence of a chitinase of 626 bp from which a putative 74-amino acid sequence, disrupted by one intron, was deduced. High degrees of homology with several plant chitinases, including those expressed during somatic embryogenesis or in seeds, were observed. P184 microsequences match the corresponding sequence deduced from the chitinase PCR-fragment perfectly.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical sciences 26 (1984), S. 2247-2248 
    ISSN: 1573-8795
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 81 (1974), S. 363-372 
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A new method is proposed for the isolation of tobacco mesophyll protoplasts in which salts were used as the plasmolyticum instead of the traditionally applied sugars. With this method protoplasts were regularly obtained and practically independent of the physiological state of the plants. In addition, a salt medium was developed in which the majority of protoplasts dedifferenciate and divide at a developmental state in which no wall could be detected by plasmolysis. After transferring these cells into another medium they were able to regenerate a wall and to divide.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-2048
    Keywords: Cell wall formation ; Cytokinesis ; Inhibitors ; Mitosis ; Nicotiana
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of cytochalasin B, colchicine, coumarin and 2,6-dichlorobenzonitrile on cell wall formation and cellular division was studied by light and electron microscopy with tobacco mesophyll protoplasts cultivated in vitro. 2,6-dichlorobenzonitrile was found to be the most effective and reversible inhibitor of cell wall formation. The other inhibitors caused irreversible damage and/or inhibited mitosis. In protoplasts cultivated in the presence of 2,6-dichlorobenzonitrile the total inhibition of cell wall formation had no effect on nuclear division, but cytokinesis was totally inhibited so that multinucleate protoplasts were obtained.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Upon disk-electrophoresis with guaiacol as a substrate the peroxidase-isoenzymes of Nicotiana tabacum (L.) were localized on the gels in two anodic and two cathodic groups. By preparation of protoplasts and isolation of cell walls it was possible to show that only cathodic enzymes are located in the protoplasts in measurable amounts, whereas all the isoenzymes, anodic and cathodic, can be found associated with cell walls. The different groups of isoenzymes are bound to the cell wall in different ways as evidenced by differences in their extration. It seems possible that different biological functions are associated with the different groups of isoenzymes. The isoenzyme patterns of different organs and tissues of tobacco show qualitative differences only in the anodic (i.e. wall located) isoenzymes. It is suggested that the ontogenetic change in peroxidase-patterns is direct evidence of biochemical differences in the cell walls of the different tissues and organs.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Planta 142 (1978), S. 11-21 
    ISSN: 1432-2048
    Keywords: Budding ; Cleavage ; Mesophyll ; Protoplasts ; Tobacco
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Tobacco (Nicotiana tabacum L., cv. Maryland) mesophyll protoplasts cultivated in saline medium divide by bud formation, migration of one nucleus into the bud, and subsequent furrowing. This process was investigated light and electron microscopically. The cytoplasm of the growing bud is richer in dictyosomes, rough endoplasmic reticulum profiles, mitochondria, and small vacuoles than is the cytoplasm of the mother cell, but in early stages lacks plastids. Only patches of wall material are found; most of the cell surface appears naked. Oriented sections of the cleavage furrow do not reveal a contractile ring of microfilaments under the fixation conditions used. The furrow is flanked by numerous microtubules, and is rich in coated vesicles. Nuclear division appears normal, but the phragmoplast vesicles appear empty, and the phragmoplast seems to disintegrate again later. The nucleus migrating into the bud does not show any signs of associated contractile structures. The results demonstrate that, in principle, higher plant cells are capable of a mode of division usually said to be “yeast-like”. The events of karyokinesis and cell plate formation are not therefore obligatorily linked processes.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two saline media, differing primarily in the presence or absence of NH4 + but also in the concentration of sucrose, were developed for culture of tobacco (Nicotiana tabacum L.) mesophyll protoplasts. In the R0.6 medium, which does not contain NH4 + and only 1 g/l sucrose, protoplasts divide 2–3 times by budding and form only a pseudo-wall, i.e. a nonrigid structure containing polysaccharides. Later the cells degenerate, and sustained division does not take place. In the W 0.6 medium, which contains NH4 + and 30 g/l sucrose, the protoplasts form a rigid wall and divide by cleavage of the cells. After a few divisions, the walls of practically all of the newly formed cells degenerate into pseudo-walls, and the divisions cease. Only a few cells keep a wall, continue to divide, and form colonies. A very high frequency of colony formations from protoplasts is obtained by culturing protoplasts for a week in R0.6 or W 0.6 and then diluting the culture with a sugar medium. A detailled study of the inorganic and organic components of the saline media showed a strong interaction between the nitrogen supply and the cytokinin requirement. The advantages of the saline media in obtaining cell colonies from protoplasts, the problems associated with budding-type division, the causes of the cessation of division when no complete wall is formed, and the conditions necessary for wall formation are discussed.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary When tobacco (Nicotiana tabacum L.) mesophyll protoplasts are cultivated in a medium in which osmotic pressure is maintained by using salts instead of sugars they divide 2–3 times although they never form a rigid wall which could be separated from the cytoplasm by the use of plasmolysis. Only a non-rigid pseudo-wall is present during division, showing that a rigid wall is not required for cell division. Diluting the salt medium with 5 volumes of sugar medium leads to the formation of a rigid wall as well as the initiation of sustained divisions. It is proposed that the complete wall is the place of synthesis of the substance(s) necessary for the division activity of the cytoplasm.
    Type of Medium: Electronic Resource
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