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  • 1
    Electronic Resource
    Electronic Resource
    Integration of signalling pathways in the establishment of the legume-rhizobia symbiosis (2005)
    Oxford, UK; Malden, USA : Munksgaard International Publishers
    Physiologia plantarum 123 (2005), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The establishment of the legume-rhizobia symbiosis requires recognition of the bacterial microsymbiont at the root epidermis followed by initiation of plant infection and nodule organogenesis programmes. These phenomena are initiated by rhizobial lipochitooligosaccharidic symbiotic signals (the Nod factors). Studies of Nod factor activities, coupled with the recent cloning of genes required for their initiation, are leading to an understanding of the first steps in the signalling pathways. Moreover studies, especially on ethylene, auxin and cytokinin, have shown that phytohormones are involved in controlling or mediating symbiotic responses. The challenge for the future will be to establish how Nod factor signalling integrates with phytohormone activities in the control of infection and nodulation in the establishment of this agronomically and ecologically important symbiosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.2005.00448.x
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  • 2
    Electronic Resource
    Electronic Resource
    The Presence of GSI-Like Genes in Higher Plants: Support for the Paralogous Evolution of GSI and GSII Genes (2000)
    Springer
    Journal of molecular evolution 50 (2000), S. 116-122 
    Details
    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
    URL: http://dx.doi.org/10.1007/s002399910013
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  • 3
    Electronic Resource
    Electronic Resource
    Expression of glutamine-synthetase genes in cotyledons of germinating Phaseolus vulgaris L. (1991)
    Springer
    Planta 183 (1991), S. 51-56 
    Details
    ISSN: 1432-2048
    Keywords: Cotyledon (glutamine synthetase) ; Gene expression (light, nitrate) ; Germination (gene expression) ; Glutamine synthetase ; Phaseolus (glutamine synthetase)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the legume Phaseolus vulgaris L., glutamine synthetase (GS; EC.6.3.1.2.) is encoded by four actively transcribed genes, gln-α, gln-β, gln-γ and gln-δ. We have studied the expression of these genes in cotyledons during seed germination and have studied the effect of light and nitrate on this process. An RNase-protection method, used to detect the abundances of GS mRNAs, revealed that the four GS genes are differentially expressed in the germinating cotyledons. The gln-α. mRNA was present in dry seeds and was the most abundant GS mRNA during early stages of germination. The gln-β and gln-γ mRNAs were first detectable 2 d after sowing and their abundances differed in light- and dark-grown cotyledons at later stages of germination. The gln-δ mRNA (which encodes the plastid-located GS) was detectable only in light-grown cotyledons, at a low abundance. A nitrate supply of 2 mM had only a minor effect on the expression of the GS genes. Western immunodetection and ion-exchange high-performance liquid chromatography demonstrated that the α polypeptide and isoenzyme were present in extracts of dry seeds and represented the major GS products at 2 d and 4 d. Both the β and γ polypeptides appeared at the 2-d stage. The role of differential GS gene expression in controlling cotyledonary GS activity is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197566
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  • 4
    Electronic Resource
    Electronic Resource
    Glutamine synthetase isoenzymes of Phaseolus vulgaris L.: subunit composition in developing root nodules and plumules (1989)
    Springer
    Planta 179 (1989), S. 433-440 
    Details
    ISSN: 1432-2048
    Keywords: Glutamine synthetase ; Isoenzymes ; Nodulation ; Phaseolus ; Plumule ; Root nodule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the legume Phaseolus vulgaris L., glutamine synthetase (GS) (EC.6.3.1.2.) occurs as three cytosolic polypeptides, α, β and γ, and a plastidic polypeptide, δ. This paper describes the subunit composition of active octameric GS isoenzymes from root nodules and plumules using ionexchange high-performance liquid chromatography followed by two-dimensional denaturing gel electrophoresis and Western immunodetection. Root nodules contained four separable GS activities, three of which were composed mainly of cytosolic γ, γ/β and β GS polypeptides, whereas the fourth activity, consisted of plastidic δ GS polypeptides. The increase in GS activity during nodulation was due largely to the appearance of γ-containing isoenzymes, and to a lesser extent on the δ isoenzyme, whereas the β-isoenzyme activity remained approximately constant throughout. Plumule GS from imbibed seeds was found to be composed of separate α and β isoenzymes, but 2 d after germination, plumule GS consisted of a mixture of α, α/β and β isoenzymes. The results from both nodules and plumules indicate that different cytosolic GS polypeptides in P. vulgaris are able to assemble into both homo-octameric and heterooctameric isoenzymes. Moreover, the changes in the patterns of isoenzymes observed during nodule development and plumule growth are interpreted to be caused both by temporal changes in the denovo synthesis of the polypeptides and also by their spatial separation in different cell types.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397582
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  • 5
    Electronic Resource
    Electronic Resource
    An association between photorespiration and protein catabolism: Studies with Chlamydomonas (1980)
    Springer
    Planta 150 (1980), S. 392-396 
    Details
    ISSN: 1432-2048
    Keywords: Chlamydomonas ; Nitrogen cycle, photorespiratory ; Photorespiratory nitrogen cycle ; Protein catabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Work demonstrating the operation of a photorespiratory N cycle in Chlamydomonas is described. NH3 release by this process is light dependent, sensitive to changes in pO2 and pCO2, and abolished by a photosystem II inhibitor. Evidence is presented which shows that this NH3 derives its N from protein rather than from freshly synthesised glutamate. Protein turnover is shown to provide amino-N at a rate sufficient to account for the highest photorespiratory N excretion observed suggesting that changes in excretion can be accounted for by increased catabolism of normally recirculating amino acids. It is equally possible however that a direct link between photorespiration and protein turnover exists, increased NH3 excretion resulting from enhanced protein turnover. The data suggest that if similar mechanisms operate in higher plants, previous estimates of the amount of N recycled in photorespiration may have been too high.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390175
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  • 6
    Electronic Resource
    Electronic Resource
    Glutamine synthetase of Chlamydomonas: Rapid reversible deactivation (1981)
    Springer
    Planta 152 (1981), S. 587-591 
    Details
    ISSN: 1432-2048
    Keywords: Chlamydomonas ; Chlorophyta ; Glutamine synthetase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A 70% reduction in glutamine synthetase (GS) activity was observed within 5 min when 5 mM NH3 and darkness was applied to steady-state cells of Chlamydomonas utilising NO3. The enzyme was reactivated in vivo by reillumination of the culture and in vitro by treatment with thiol reagents. The activity modulations affected the synthetase and transferase activities similarly and were not influenced by protein synthesis inhibitors. Deactivation of GS was also observed when steady-state cells were treated with an uncoupler of phosphorylation, carbonylcyanide m-chlorophenylhydrazone (CCCP) or inhibitors of the electron transport chain but under these conditions the activity modulation affected over 90% of the activity and was irreversible. The mechanism of the physiological deactivation of GS is discussed in relation to both the in vivo and in vitro findings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00380832
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  • 7
    Electronic Resource
    Electronic Resource
    Glutamine synthetase of Chlamydomonas: its role in the control of nitrate assimilation (1981)
    Springer
    Planta 153 (1981), S. 18-24 
    Details
    ISSN: 1432-2048
    Keywords: Chlamydomonas ; Glutamine synthetase ; Nitrate assimilation (regulation) ; Nitrale reductase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Work is described which suggests that glutamine synthetase (GS) could play an important and direct regulatory role in the control of NO3 assimilation by the alga. In both steady-state cells and ones disturbed physiologically by changes in light or nitrogen supply the assimilation of NO3 appears to be limited by the activity of GS. Moreover although in normal cells NH3 can completely inhibit NO3 uptake, promote the deactivation of nitrate reductase (NR) and repress the synthesis of NR and nitrite reductase (NIR), these controls are relaxed in cells in which GS is deactivated by treatment with L-methionine-DL-sulfoximine (MSO). It is proposed that the reversible deactivation of GS may play an important part in the regulation of NO3 assimilation although it is still not clear whether the enzyme itself or products of its metabolism are responsible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385313
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  • 8
    Electronic Resource
    Electronic Resource
    cDNA sequence and differential expression of the gene encoding the glutamine synthetase γ polypeptide ofPhaseolus vulgaris L. (1989)
    Springer
    Plant molecular biology 12 (1989), S. 553-565 
    Details
    ISSN: 1573-5028
    Keywords: cDNA sequence ; gene expression ; glutamine synthetase ; legume-Rhizobium symbiosis ; nitrogen metabolism ; Phaseolus vulgaris L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We report the sequence of an essentially full-length glutamine synthetase (GS) cDNA clone (pcGS-γ1) isolated from a root nodule library ofPhaseolus vulgaris L. The polypeptide encoded by this cDNA has been producedin vitro by transcription/translation and shown to co-migrate on two-dimensional gels with the previously identified major cytosolic GS polypeptide (γ) of nodules. Two previously identified GS cDNA clones, pR-2 and pR-1 (see Gebhardtet al., EMBO J 5: 1429–1435, 1986) have similarly been shown to encode the α and β cytosolic GS polypeptides respectively. An RNase protection technique has been used to analyse specifically and quantitatively the abundance of mRNA related to these three GS cDNAs and to the cDNA (pcGS-δ1) encoding the chloroplast-located GS, during nodulation. Differences in the abundances of these mRNAs at different times suggest that they are not coordinately regulated. Moreover, using this technique mRNA specifically related to pcGS-γ1 was found at high levels in nodules but not in roots or leaves. Surprisingly the expression of this gene is not nodule-specific as previously suggested, as its mRNA was also detected, but at lower levels, in stems, petioles and in green cotyledons. By comparison, mRNA related to a leghaemoglobin gene was detected only in nodules. Comparisons of the relative abundances of the pcGS-γ1 mRNA and the γ polypeptide in different organs and at different stages during nodulation, suggest that the appearance of the γ polypeptide is largely under transcriptional control.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00036969
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  • 9
    Electronic Resource
    Electronic Resource
    Expression of glutamine synthetase genes in roots and nodules of Phaseolus vulgaris following changes in the ammonium supply and infection with various Rhizobium mutants (1990)
    Springer
    Plant molecular biology 14 (1990), S. 549-560 
    Details
    ISSN: 1573-5028
    Keywords: gene expression ; glutamine synthetase ; leghaemoglobin ; nitrogen metabolism ; Phaseolus vulgaris ; root nodules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this paper we have examined whether the four glutamine synthetase (gln) genes, expressed in roots and nodules of Phaseolus vulgaris are substrate-inducible by ammonium. Manipulation of the ammonium pool in roots, through addition and removal of exogenous ammonium, did not elicit any changes in the abundances of the four mRNAs thus suggesting that the gln genes in roots of this legume are neither substrate-inducible by ammonium nor derepressed during nitrogen starvation. In nodules the effect of the ammonium supply on expression of the gln genes has been examined by growing nodules under argon/oxygen atmospheres, or with a number of Fix- Rhizobium mutants, and following addition of exogenous ammonium. The results of these experiments suggest that the expression of the gln-γ gene, which is strongly induced during nodule development, is primarily under a developmental control. However nitrogen fixation appears to have a quantitative effect on expression of gln-γ as the abundance of this mRNA is about 2 to 4-fold higher under nitrogen-fixing conditions. This effect could not be mimicked by addition of exogenous ammonium and moreover is not specific to the gln-γ gene as mRNA from a leghaemoglobin gene was similarly affected. Taken together these results have failed to find an effect of ammonium on specifically inducing the expression of glutamine synthetase genes in roots and nodules of P. vulgaris.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00027500
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  • 10
    Electronic Resource
    Electronic Resource
    Regulation of glutamine synthetase genes in leaves of Phaseolus vulgaris (1991)
    Springer
    Plant molecular biology 17 (1991), S. 761-771 
    Details
    ISSN: 1573-5028
    Keywords: glutamine synthetase ; leaves ; light regulation ; nitrogen metabolism ; Phaseolus vulgaris ; photorespiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Glutamine synthetase (GS) activity increased over three-fold in developing primary leaves of Phaseolus vulgaris L. This increase was shown to be the result of differential expression of three members of the GS gene family: gln-α and gln-β, which encode cytosolic GS polypeptides, and gln-δ, which encodes the chloroplast-located GS. The gln-δ gene was the most highly expressed GS gene and was regulated in a complex manner with two different transcripts accumulating differentially during leaf development. This gene was expressed weakly in the dark and was induced strongly by lingt; this induction was shown not to be an indirect effect of photorespiration. In the long term, gln-δ showed increased expression in photorespiring compared with non-photorespiring leaves. However, in the short term, there was no induction of gln-δ following transfer of plants to photorespiratory conditions. These results suggest that regulation of gln-δ by photorespiration was the result of indirect, long-term effects on cellular metabolism. In general, in all these experiments, analysis of cytosolic versus chloroplastic GS polypeptides and of the GS isoenzyme profiles showed the same pattern of changes in abundance as that observed for the mRNAs suggesting that regulation of GS gene expression occurred primarily at the mRNA level. However, it was noteworthy that the δ isoenzyme remained at a high abundance in older leaves, grown in both light and dark, despite a decrease in abundance of gln-δ mRNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00037059
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