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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Location of two isoenzymes of NADH-dependent glutamate synthase in root nodules of Phaseolus vulgaris L. (1989)
    Springer
    Planta 179 (1989), S. 441-447 
    Details
    ISSN: 1432-2048
    Keywords: Glutamate synthase ; Glutamine synthetase ; Nitrogen fixation ; Phaseolus (glutamate synthase) ; Plastid (glutamate synthase) ; Root nodule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The two isoenzymes of NADH-dependent glutamate synthase (NADH-GOGAT; EC 1.4.1.14), previously identified in root nodules of Phaseolus vulgaris L., have both been shown to be located in root-nodule plastids. The nodule specific NADH-GOGAT II accounts for the majority of the activity in root nodules, and is present almost exclusively in the central tissue of the nodule. However about 20% of NADH-GOGAT I activity is present in the nodule cortex, at about the same specific activity as this isoenzyme is found in the central tissue. Glutamine synthetase (GS; EC 6.3.1.2) occurs predominantly as the γ polypeptide in the central tissue, whereas in the cortex, the enzyme is represented mainly by the β polypeptide. Over 90% of both GS and NADH-GOGAT activities are located in the central tissue of the nodule and GS activity exceeds NADH-GOGAT activity by about twofold in this region. Using the above information, a model for the subcellular location and stoichiometry of nitrogen metabolism in the central tissue of P. vulgaris root nodules is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397583
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Purification and properties of two forms of glutamine synthetase from the plant fraction of Phaseolus root nodules (1983)
    Springer
    Planta 157 (1983), S. 245-253 
    Details
    ISSN: 1432-2048
    Keywords: Glutamine synthetase ; Legume ; Rhizobium symbiosis ; Nitrogen assimilation ; Phaseolus (glutamine synthetase) ; Rhizobium ; Root nodule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two forms of glutamine synthetase (GS) have been purified to apparent homogeneity from the plant fraction of Phaseolus vulgaris root nodules. One of these forms appears identical to the form of the enzyme found in roots but the other is probably specifically associated with the nodule. Free-living Rhizobium phaseoli also contain two forms of GS both of which have different molecular weights from the plant enzymes. Bacteroids contain solely the higher-molecular-weight form of rhizobial GS. There are only minor differences between the plant enzymes in Km or S0.5 values for the synthetase-reaction substrates and both forms have identical molecular weights of the holoenzyme (380,000 daltons) and its sub-units (41,000 daltons). They can be separated by ion-exchange chromatography on diethylaminoethyl-Sephacel and by native polyacrylamide-gel electrophoresis. The only other distinguishing feature observed is that the ratio of transferase: synthetase activity of the root form is threefold greater than that of the nodule-specific GS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00405189
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  • 10
    Electronic Resource
    Electronic Resource
    Appearance of a novel form of plant glutamine synthetase during nodule development in Phaseolus vulgaris L. (1983)
    Springer
    Planta 157 (1983), S. 254-258 
    Details
    ISSN: 1432-2048
    Keywords: Glutamine synthetase ; Leghaemoglobin ; Nitrogenase ; Nitrogen fixation ; Phaseolus ; Rhizobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activities of glutamine synthetase (GS), nitrogenase and leghaemoglobin were measured during nodule development in Phaseolus vulgaris infected with wild-type or two non-fixing (Fix-) mutants of Rhizobium phaseoli. The large increase in GS activity which was observed during nodulation with the wild-type rhizobial strain occurred concomitantly with the detection and increase in activity of nitrogenase and the amount of leghaemoglobin. Moreover, this increase in GS was found to be due entirely to the appearance of a novel form of the enzyme (GSn1) in the nodule. The activity of the form (GSn2) similar to the root enzyme (GSr) remained constant throughout the experiment. In nodules produced by infection with the two mutant strains of Rhizobium phaseoli (JL15 and JL19) only trace amounts of GSn1 and leghaemoglobin were detected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00405190
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