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  • 1
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    Betaxanthin formation and free amino acids in hairy roots of Beta vulgaris var. lutea depending on nutrient medium and glutamate or glutamine feeding (2004)
    Elsevier
    Details
    Publication Date: 2004-05-01
    Print ISSN: 0031-9422
    Electronic ISSN: 1873-3700
    Topics: Biology , Chemistry and Pharmacology
    Published by Elsevier
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  • 2
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    Glutamine synthetase isoenzymes, oligomers and subunits from hairy roots of Beta vulgaris L. var. lutea (1998)
    Springer
    Details
    Publication Date: 1998-04-22
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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  • 3
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    The chloroplastic glutamine synthetase (GS-2) of tobacco is phosphorylated and associated with 14-3-3 proteins inside the chloroplast (2001)
    Springer
    Details
    Publication Date: 2001-07-01
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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  • 4
    Electronic Resource
    Electronic Resource
    New insights towards the function of glutamate dehydrogenase revealed during source-sink transition of tobacco (Nicotiana tabacum) plants grown under different nitrogen regimes (2004)
    Oxford, UK; Malden , USA : Munksgaard International Publishers
    Physiologia plantarum 120 (2004), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The metabolic, biochemical and molecular events occurring in the different leaf stages along the main axis of tobacco (Nicotiana tabacum) plants grown either on a nitrogen-rich medium, on a medium containing ammonium as sole nitrogen source or on a nitrogen-depleted medium, are presented. This study shows that the highest induction of cytosolic glutamine synthetase (GS1) protein and transcript occurs when nitrogen remobilization is maximal as the result of nitrogen starvation, whereas both glutamate dehydrogenase (GDH) transcript and activity remain at a very low level. In contrast, GDH is highly induced when plants are grown on ammonium as sole nitrogen source, a physiological situation during which leaf protein nitrogen remobilization is limited. It is therefore concluded that GDH does not play a direct role during the process of nitrogen remobilization but is rather induced following a built up of ammonium provided externally or released as the result of protein hydrolysis during natural leaf senescence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0031-9317.2004.0241.x
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  • 5
    Electronic Resource
    Electronic Resource
    Cytosolic and chloroplastic glutamine synthetase of sugarbeet (Beta vulgaris) respond differently to organ ontogeny and nitrogen source (2000)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 108 (2000), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Changes in the activity and subunit composition of cytosolic glutamine synthetase (GS 1; EC 6.3.1.2) and chloroplastic GS (GS 2) were studied in response to an internal (organ ontogeny) and external signal (N source: NO3− or NH4+). Maximum GS 1 activity of all organs examined was measured in the fibre roots, irrespective of the N source. The response of GS 1 to the N source was, however, organ specific. In the fibre roots, NH4+ nutrition resulted in a 2- to 7-fold (based on protein or freshweight, respectively) increase of GS 1 activity compared to NO3−-grown plants. In contrast to the roots, GS 1 activity in the leaf blades was 2-fold lower with NH4+ nutrition, whereas only minor changes occurred in the petioles. GS 2 activity was highest in the mature and senescing leaf blade; activity was 2-fold higher with NH4+ than with NO3− nutrition. Not only activity, but also subunit composition of GS 1 changed during organ ontogeny as well as in response to the N source. In contrast to GS 1, only minor changes were evident in GS 2 subunit composition, despite significant changes in GS 2 activity. Up to 5 different GS 1 subunits of ≈41–43 kDa were separated; they were identical in all organs examined. GS 2 was composed of 4 different subunits of ≈48 kDa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.2000.108003263.x
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  • 6
    Electronic Resource
    Electronic Resource
    Organ-specific changes in the activity and subunit composition of glutamine-synthetase isoforms of barley (Hordeum vulgare L.) after growth on different levels of NH+ 4 (1995)
    Springer
    Planta 196 (1995), S. 231-238 
    Details
    ISSN: 1432-2048
    Keywords: Ammonium (organ-specific effect) ; Glutamine synthetase (isoforms, subunit composition) ; Hordeum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract One cytosolic glutamine synthetase (GS, EC 6.3.1.2) isoform (GS 1a) was active in the germinating seeds of barley (Hordeum vulgare L.). A second cytosolic GS isoform (GS 1b) was separated from the leaves as well as the roots of 10-d-old seedlings. The chloroplastic isoform (GS 2) was present and active only in the leaves. The three GS isoforms were active in N-supplied (NH+ 4 or NO 3 − ) as well as in N-free-grown seedlings. This indicates (i) that a supply of nitrogen to the germinating seeds was not necessary for the induction of the GS isoforms and (ii) that no nitrogen-specific isoforms appeared during growth of seedlings with different nitrogen sources. The activity of GS, however, depended on the seedlings' nitrogen source: the specific activity was much higher in the leaves and much lower in the roots of NH+ 4-grown barley than in the respective organs of NO 3 − -fed or N free-grown plants. With increasing concentrations of NH+ 4 (supplied hydroponically during growth), the specific activity of GS 1b increased in the leaves, but decreased in the roots. The activity of GS 2 (leaf) also increased with increasing NH+ 4 supply, whereas GS 1a activity (leaf and root) was not affected. The changes in the activities of GS 1b and GS 2 were correlated with changes in the subunit compositions of the active holoenzymes: growth at increased levels of external NH+ 4 resulted in an increased abundance of one of the four GS subunits, and of two of the five GS 1b subunits in the leaves. In the roots, however, the abundance of these two GS 1b subunits was decreased under the same growth conditions, indicating an organ-specific difference either in the expression of the genes coding for the respective GS 1b subunits or in the assembly of the GS 1b holoenzymes. Furthermore, growth at different levels of NH+ 4 resulted in changes in the substrate affinities of the isoforms GS 1b (root and leaf) and GS 2 (leaf), presumably due to the changes in the subunit compositions of the active holoenzymes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201379
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  • 7
    Electronic Resource
    Electronic Resource
    Glutamine synthetase isoenzymes, oligomers and subunits from hairy roots of Beta vulgaris L. var. lutea (1998)
    Springer
    Planta 205 (1998), S. 113-120 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Beta ; Glutamine synthetase ; Hairy roots ; Isoenzyme (GS oligomers ; subunits) ; Nitrogen meta‐bolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. A cytosolic and a plastidic isoenzyme of glutamine synthetase (GS; EC 6.3.1.2) were separated from hairy roots of Beta vulgaris L. var. lutea. The predominant activity was that of cytosolic GS 1; the relative proportion of plastidic GS 2 activity changed, however, depending on the growth conditions. Maximum activity of both isoenzymes was measured after growth with NO− 3 as the major N-source. Growth with NH+ 4 as the sole N-source or growth in constant darkness resulted in a significant decrease in GS 1 activity, whereas GS 2 activity was much less effected and thus contributed as much as 25% of total root GS activity. The isoenzymes GS 1 and GS 2 were active both in the octameric and tetrameric states. Both oligomers of GS 2 and octameric GS 1 were active under all growth conditions applied whereas tetrameric GS 1 was not active when the roots were grown under light-dark changes with NO− 3 as the major N-source. The molecular masses of the subunits were identical for both isoenzymes. Glutamine synthetase 1 was composed of up␣to four different 38-kDa subunits and two different 41-kDa subunits; GS 2 was assembled from one type of 38-kDa subunit and one type of 41-kDa subunit. The GS␣2 subunits were most probably identical to two of the GS␣1 subunits. The subunit composition of GS 1, but not of GS 2, changed depending on the growth conditions of the roots. Changes in GS 1 subunit composition were correlated with changes in GS 1 activity. The different growth conditions induced the specific assembly of different GS 1 isoenzymes which could, however, not be separated by anion-exchange chromatography but became evident only after two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050302
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  • 8
    Electronic Resource
    Electronic Resource
    Glutamine synthetase oligomers and isoforms in sugarbeet (Beta vulgaris L.) (1990)
    Springer
    Planta 181 (1990), S. 10-17 
    Details
    ISSN: 1432-2048
    Keywords: α-Amino nitrogen ; Beta (glutamine synthetase) ; Glutamine synthetase (isoforms, oligomers)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The α-amino-N compounds that accumulate in the thickening storage root of sugarbeet (Beta vulgaris L.) were synthesized in the leaves (NO 3 − nutrition) and also in the lateral roots (NH 4 + nutrition). Ammonium stimulated glutamine synthetase (GS, EC 6.3.1.2) activity, especially in the lateral roots. With non-denaturing polyacrylamide-gel isoelectric focussing, simultaneously active charge-isomers of GS were separated in both leaves and roots. The leaf isoforms were active in an octameric and also in a tetrameric form. In the root only octameric isoforms were found. The tetramer was more active than the octamer in the leaf blade and vice versa in the leaf stem. Only the tetramer needed β-mercaptoethanol for activity stabilization in vitro. A reactivation, however, of an inactive tetramer by the addition of thiol/thioredoxin was not possible. The same isoforms of GS were separated in different organs of sugarbeet but with different patterns of relative activity. The activity pattern depended also on the N-source of the plant. With increasing age of the plant the number of active GS isoforms declined in both leaves and roots although the in-vitro activity remained unchanged (NO 3 − -fed plants) or even increased (NH 4 + -fed plants).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202319
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  • 9
    Electronic Resource
    Electronic Resource
    The effect of endogenous and externally supplied nitrate on nitrate uptake and reduction in sugarbeet seedlings (1990)
    Springer
    Planta 182 (1990), S. 169-173 
    Details
    ISSN: 1432-2048
    Keywords: Beta (nitrate reduction) ; Fruit (N reservoir) ; Nitrate reductase activity ; Nitrate uptake ; Pericarp (N reservoir) ; Seed (nitrate uptake)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The pericarp of the dormant sugarbeet fruit acts as a storage reservoir for nitrate, ammonium and α-amino-N. These N-reserves enable an autonomous development of the seedling for 8–10 d after imbibition. The nitrate content of the seed (1% of the whole fruit) probably induces nitrate-reductase activity in the embryo enclosed in the pericarp. Nitrate that leaks out of the pericarp is reabsorbed by the emerging radicle. Seedlings germinated from seeds (pericarp was removed) without external N-supply are able to take up nitrate immediately upon exposure via a low-capacity uptake system (vmax = 0.8 μmol NO 3 - ·(g root FW)−1·h−1; Ks = 0.12 mM). We assume that this uptake system is induced by the seed nitrate (10 nmol/seed) during germination. Induction of a high-capacity nitrate-uptake system (vmax = 3.4 μmol NO 3 - ·(g root FW)−1·h−1; Ks = 0.08 mM) by externally supplied nitrate occurs after a 20-min lag and requires protein synthesis. Seedlings germinated from whole fruits absorb nitrate via a highcapacity uptake mechanism induced by the pericarp nitrate (748 nmol/pericarp) during germination. The uptake rates of the high-capacity system depend only on the actual nitrate concentration of the uptake medium and not on prior nitrate pretreatments. Nitrate deprivation results in a decline of the nitrate-uptake capacity (t1/2 of vmax = 5 d) probably caused by the decay of carrier molecules. Small differences in Ks but significant differences in vmax indicate that the low- and high-capacity nitrate-uptake systems differ only in the number of identical carrier molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197106
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  • 10
    Electronic Resource
    Electronic Resource
    Physiological regulation of plant-atmosphere ammonia exchange (2000)
    Springer
    Plant and soil 221 (2000), S. 95-102 
    Details
    ISSN: 1573-5036
    Keywords: ammonia exchange ; apoplast ; atmosphere ; glutamine synthetase ; nitrogen ; photorespiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Plants have a compensation point for NH3 which ranges from 0.1 to 20 nmol mol-1, and may be several-fold higher or lower than naturally occurring atmospheric NH3 concentrations. This implies that NH3 fluxes over vegetated surfaces are bi-directional and that ammonia exchange with the atmosphere in many cases contributes significantly to the nitrogen economy of vegetation. Physiological regulation of plant–atmosphere NH3 fluxes is mediated via processes involved in nitrogen uptake, transport and metabolism. A rapid turnover of NH3 + in plant leaves leads to the establishment of a finite NH3 + concentration in the leaf apoplastic solution. This concentration determines, together with that of H+, the size of the NH3 compensation point. Barley and oilseed rape plants with access to NH3 + in the root medium have higher apoplastic NH3 + concentrations than plants absorbing NO3 -. Furthermore, the apoplastic NH3 + concentration increases with the external NH3 + concentration. Inhibition of GS leads to a rapid and substantial increase in apoplastic NH3 + and barley mutants with reduced GS activity have higher apoplastic NH3 + than wild-type plants. Increasing rates of photorespiration do not affect the steady-state NH3 + or H+ concentration in tissue or apoplast of oilseed rape, indicating that the NH3 + produced is assimilated efficiently. Nevertheless, NH3 emission increases due to a temperature-mediated displacement of the chemical equilibrium between gaseous and aqueous NH3 in the apoplast. Sugarbeet plants grown with NO3 - seem to be temporarily C-limited in the light due to a repression of respiration. As a consequence, the activity of chloroplastic GS declines during the day causing a major part of NH3 + liberated in photorespiration to be assimilated during darkness when 2-oxoglutarate is supplied in high rates by respiration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004761931558
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