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  • 1
    Electronic Resource
    Electronic Resource
    A few remarks on the Dauns-Hofmann theorems forC *-algebras (1984)
    Springer
    Archiv der Mathematik 43 (1984), S. 265-269 
    Details
    ISSN: 1420-8938
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01247573
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  • 2
    Electronic Resource
    Electronic Resource
    On Gröbner bases under specialization (1994)
    Springer
    Applicable algebra in engineering, communication and computing 5 (1994), S. 1-8 
    Details
    ISSN: 1432-0622
    Keywords: Polynomial ideals ; Gröbner bases ; D-Gröbner bases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics , Technology
    Notes: Abstract We extend a result of Gianni and Kalkbrener concerning the stability of the Gröbner basis property under specializations. In particular, we prove that the Gröbner basis property is preserved if one specializes variables from bottom up in a Gröbner basis of a zero-dimensional radical ideal w.r.t. a lexicographical term order. The proof makes use of a connection between Gröbner bases and D-Gröbner bases which is proved separately. Computational aspects of this connection are discussed briefly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01196621
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  • 3
    Electronic Resource
    Electronic Resource
    Reversible commitment of neural and epidermal progenitor cells during embryogenesis of Drosophila melanogaster (1988)
    Springer
    Development genes and evolution 197 (1988), S. 413-418 
    Details
    ISSN: 1432-041X
    Keywords: Cell interactions ; Cell commitment ; Neurogenesis ; Drosophila
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cell-cell interactions are involved in mediating developmental fate. An example is the decision of the neuroectodermal cells of Drosophila to develop as neural or epidermal progenitors, where cellular interactions participate in the process of acquisition of either cell fate. The results of heterochronic cell transplantations we describe here suggest that both neuroblasts and epidermoblasts are not irreversibly committed to a particular developmental fate. Rather, they retain the ability to interact with neighbouring cells and, under our experimental conditions, are capable of switching their fate during a relatively long period of time, i.e. until the end of embryonic stage 11.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00398992
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  • 4
    Electronic Resource
    Electronic Resource
    Light-regulated expression of the nitrate-reductase and nitrite-reductase genes in tomato and in the phytochrome-deficient aurea mutant of tomato (1992)
    Springer
    Planta 188 (1992), S. 39-47 
    Details
    ISSN: 1432-2048
    Keywords: Gene expression ; Lycopersicon ; Mutant (tomato, aurea) ; Nitrate reductase ; Nitrite reductase ; Phytochrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The phytochrome-deficient aurea mutant of tomato (Lycopersicon esculentum (L.) Mill) was used to investigate if phytochrome plays a role in the regulation of nitrate-reductase (NR, EC 1.6.6.1) and nitrite-reductase (NiR, EC 1.7.7.1) gene expression. We show that the expression of the tomato NR and NiR genes is stimulated by light and that this light response is mediated by the photoreceptor phytochrome. The red-light response of the NR and NiR genes was reduced in etiolated aurea seedlings when compared to isogenic wild-type cotyledons. The relative levels of NR mRNA and NiR transcripts and their diurnal fluctuations were identical in mature white-light-grown leaves of the wild-type and of the aurea mutant. The transcript levels for cab and RbcS (genes for the chlorophyll-a/b-binding protein of PSII and the small subunit of the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase, respectively) in aurea leaves grown in white light were indistinguishable from the respective transcript levels in the leaves of the wildtype grown under the same conditions. Despite a severe reduction in the chlorophyll content, the rate of net CO2 uptake by leaves of the aurea mutant was only slightly reduced when compared to the rate of net photosynthesis of wild-type leaves. This difference in the photosynthetic performances of wild-type and aurea mutant plants disappeared during aging of the plants. The increase in zeaxanthin and the concomitant decrease in violaxanthin in leaves of the aurea mutant compared with the same pigment levels in leaves of the wild-type indicate that the activity of the xanthophyll cycle is increased in aurea leaves as a consequence of the reduced CO2-fixation capacity of the mutant leaves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198937
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  • 5
    Electronic Resource
    Electronic Resource
    Light-regulated expression of the nitrate-reductase and nitrite-reductase genes in tomato and in the phytochrome-deficientaurea mutant of tomato (1992)
    Springer
    Planta 188 (1992), S. 39-47 
    Details
    ISSN: 1432-2048
    Keywords: Gene expression ; Lycopersicon ; Mutant (tomato,aurea) ; Nitrate reductase ; Nitrite reductase ; Phytochrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The phytochrome-deficientaurea mutant of tomato (Lycopersicon esculentum (L.) Mill) was used to investigate if phytochrome plays a role in the regulation of nitrate-reductase (NR, EC 1.6.6.1) and nitrite-reductase (NiR, EC 1.7.7.1) gene expression. We show that the expression of the tomato NR and NiR genes is stimulated by light and that this light response is mediated by the photoreceptor phytochrome. The red-light response of the NR and NiR genes was reduced in etiolatedaurea seedlings when compared to isogenic wild-type cotyledons. The relative levels of NR mRNA and NiR transcripts and their diurnal fluctuations were identical in mature white-light-grown leaves of the wild-type and of theaurea mutant. The transcript levels forcab andRbcS (genes for the chlorophyll-a/b-binding protein of PSII and the small subunit of the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase, respectively) inaurea leaves grown in white light were indistinguishable from the respective transcript levels in the leaves of the wildtype grown under the same conditions. Despite a severe reduction in the chlorophyll content, the rate of net CO2 uptake by leaves of theaurea mutant was only slightly reduced when compared to the rate of net photosynthesis of wild-type leaves. This difference in the photosynthetic performances of wild-type andaurea mutant plants disappeared during aging of the plants. The increase in zeaxanthin and the concomitant decrease in violaxanthin in leaves of theaurea mutant compared with the same pigment levels in leaves of the wild-type indicate that the activity of the xanthophyll cycle is increased inaurea leaves as a consequence of the reduced CO2-fixation capacity of the mutant leaves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01160710
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  • 6
    Electronic Resource
    Electronic Resource
    Negative regulation of nitrate reductase gene expression by glutamine or asparagine accumulating in leaves of sulfur-deprived tobacco (2000)
    Springer
    Planta 211 (2000), S. 587-595 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Amino acid – Glutamine synthetase – Nitrate assimilation – Nitrate reductase –Nicotiana (sulfur-deprivation) – Sulfur-deprivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract.  Tobacco (Nicotiana tabacum L.) plants were subjected to a prolonged period of sulfur-deprivation to characterize molecular and metabolic mechanisms that permit control of primary N-metabolism under these conditions. Prior to the appearance of chlorotic lesions, sulfur-deprived tobacco leaves showed a strong decrease in the sulfate content and changes in foliar enzyme activities, mRNA accumulation and amino-acid pools. The basic amino acids glutamine, asparagine and arginine accumulated in the leaves of sulfur-deprived plants, while the foliar concentrations of aspartate, glutamate, serine or alanine remained fairly unchanged. Maximal extractable nitrate reductase (NR; EC 1.6.6.1) activity decreased strongly in response to sulfur-deprivation. The decrease in maximal extractable NR activity was accompanied by a decline in NR transcripts while the mRNAs of the plastidic glutamine synthetase (EC 6.1.3.2) or the β-subunit of the mitochondrial ATP synthase were much less affected. Nitrate first accumulated in leaves of tobacco during sulfur-deprivation but then declined. An appreciable amount of nitrate was, however, present in severely sulfur-depleted leaves. The repression of NR gene expression is, therefore, not related to the decrease in the leaf nitrate level. However, glutamine- and/or asparagine-mediated repression of NR gene transcription is a possible mechanism of control in situations when glutamine and asparagine accumulate in leaves and provides a feasible explanation for the reduction in NR activity during sulfur-deprivation. The removal of reduced nitrogen from primary metabolism by redirection and storage as arginine, asparagine or glutamine combined with the down-regulation of nitrate reduction via glutamine- and/or asparagine-mediated repression of NR gene transcription may contribute to maintaining a normal N/S balance during sulfur-deprivation and indicate that the co-ordination of N- and S-metabolism is retained under these conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250000322
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  • 7
    Electronic Resource
    Electronic Resource
    Photosynthesis and fluorescence quenching, and the mRNA levels of plastidic glutamine synthetase or of mitochondrial serine hydroxymethyltransferase (SHMT) in the leaves of the wild-type and of the SHMT-deficient stm mutant of Arabidopsis thaliana in relation to the rate of photorespiration (1997)
    Springer
    Planta 202 (1997), S. 379-386 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Arabidopsis (stm mutant) ; Gas exchange ; Gene expression ; Glutamine synthetase ; Mutant (Arabidopsis ; stm) ; Photorespiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The regulation by photorespiration of the transcript level corresponding to plastidic glutamine synthetase (GS-2) was investigated in the leaves of Arabidopsis thaliana (L.) Heynh.. Photorespiration was suppressed by growing the plants in an atmosphere containing 300 Pa CO2. Suppression of photorespiration was demonstrated by the ability of the conditionally lethal serine hydroxymethyltransferase (SHMT)-deficient stm mutant of A. thaliana to grow normally under these conditions. In contrast to previous studies with bean or pea that were performed at very high CO2 partial pressure (2–4 kPa; Edwards and Coruzzi, 1989, Plant Cell 1: 241–248; Cock et al., 1991, Plant Mol Biol 17: 761–771), suppression of photorespiration during growth of A. thaliana in an atmosphere with 300 Pa CO2 had no effect on the leaf GS-2 transcript level. In the short term, neither suppression of photorespiration induced by the transfer of air-grown A. thaliana plants into a CO2-enriched atmosphere, nor an increase in the rate of photorespiration achieved by the transfer of high-CO2-grown A. thaliana plants into air resulted in a change in the GS-2 mRNA level. The absence of photorespiratory ammonium release in leaves of the stm mutant had no effect on the GS-2 transcript level. Overall, our data argue against a control by photorespiration of the A. thaliana leaf GS-2 mRNA pool. In contrast, regulation of the leaf SHMT mRNA level may involve a negative feedback effect of at least one metabolite derived from the glycine/serine conversion during photorespiration, as indicated by the overexpression of SHMT transcripts in the leaves of the stm mutant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050140
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  • 8
    Electronic Resource
    Electronic Resource
    Two nitrite reductase isoforms are present in tomato cotyledons and are regulated differently by UV-A or UV-B light and during plant development (1998)
    Springer
    Planta 207 (1998), S. 229-234 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Gene expression ; Isoenzyme ; Light-regulation ; Lycopersicon ; Nitrite reductase ; Ultraviolet light
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The regulation by UV-A or UV-B light of the nuclear gene(s) encoding the plastidic enzyme nitrite reductase (NiR; EC 1.7.7.1) was examined in the cotyledons of tomato (Lycopersicon esculentum L.). Two NiR isoforms designated NiR1 and NiR2 with apparent molecular masses of 63 kDa and 62 kDa, respectively, were detected by immunoblot analysis in total soluble protein extracts derived from tomato seedling cotyledons. Genomic Southern blot analysis indicated the presence of two NiR genes per haploid tomato genome. In etiolated tomato cotyledons, the total NiR protein pool was almost exclusively constituted by NiR1. In contrast, NiR2 was the predominant NiR isoform in the cotyledons of tomato seedlings grown in white light. Illumination of etiolated tomato cotyledons with UV-A or UV-B light resulted in an increase in both the total NiR transcript level and the NiR2 protein abundance. Blue light stimulated the NiR2 protein pool above the level obtained with red light of equal photon fluence rate. These results show that NiR2 protein expression is light-inducible and that the light-stimulation of NiR2 protein accumulation involves the action of both phytochrome and a specific blue-light photoreceptor. The NiR1 protein level remained virtually unaffected by the light treatments. The change in the relative proportion of the NiR isoforms during greening of etiolated tomato cotyledons is, therefore, due to the different light-responsiveness of the genes corresponding to NiR1 or NiR2. The physiological significance of the presence of NiR isoforms that are regulated differently by light in tomato cotyledons is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050477
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  • 9
    Electronic Resource
    Electronic Resource
    Regulation of the subunit composition of tomato plastidic glutamine synthetase by light and the nitrogen source (1996)
    Springer
    Planta 200 (1996), S. 213-220 
    Details
    ISSN: 1432-2048
    Keywords: Gene expression ; Glutamine synthetase ; Nitrogen source ; Phosphinothricin ; Phytochrome ; Solanum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The co-action of light and the N-source in the regulation of the expression of the single-copy gene encoding plastidic glutamine synthetase (GS-2) and of the multigene family encoding cytosolic glutamine synthetase (GS-1) was investigated in the cotyledons of tomato (Lycopersicon esculentum L.). Light, acting at red/far red or at blue regions of the spectrum increased the abundance of the GS-2 gene product and induced a modification of GS-2 subunits, resulting in the appearance of two GS-2 proteins exhibiting different molecular weights. The magnitude of the light stimulation of GS-2 gene expression was independent of the nitrogen source. However, following red- or far-red-light treatment of etiolated tomato cotyledons, two GS-2 proteins were found when nitrate was the N-source, while only one GS-2 protein was present with ammonium as the sole nitrogen source. Thus, light of specific wavelengths and N-substrates seem to act in concert to regulate GS-2 subunit composition. Tomato GS-1 gene expression was unaffected by light. Ammonium provided externally increased the level of the tomato GS-1 protein. Irrespective of the N-source or the light quality, the GS-1 subunits were represented by polypeptides of similar molecular weight in tomato cotyledons. However, phosphinothricin-induced inhibition of GS activity resulted in the appearance of at least one additional GS-1 polypeptide in etiolated or in green tomato cotyledons. In addition, impairment of GS activity in green tomato cotyledons by phosphinothricin was correlated with an increased level of the GS-1 transcript. Taken together, our data suggest a metabolic control of GS-1 gene expression in green tomato cotyledons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00208311
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  • 10
    Electronic Resource
    Electronic Resource
    Thecab-m7 gene: a light-inducible, mesophyll-specific gene of maize (1992)
    Springer
    Plant molecular biology 20 (1992), S. 49-60 
    Details
    ISSN: 1573-5028
    Keywords: Zea mays L. ; cell type specificity ; light inducibility ; monocot conserved sequences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Southern blot analysis has revealed the existence in maize of perhaps 12 members of the nuclearcab multigene family encoding the chlorophylla- andb-binding proteins of the photosystem II light-harvesting complex. Hybridization with 3′ probes derived from unsequenced cDNA clones showed that six members of this family differ from one another with respect to expression in mesophyll and/or bundle sheath cells and regulation by light. An additional member of this family, designatedcab-m7, that encodes a 28 kDa primary translation product has now been identified. It has been cloned from a maize genomic library and sequenced to begin to define the bases for differences in the expression of these genes. Thiscab gene is shown to be strongly preferentially expressed in the mesophyll (vs. bundle sheath) cells of maize. Furthermore, the gene is photo-responsive; although small amounts ofcab-m7 mRNA are present in etiolated leaves, the mRNA pool is 8-fold larger after six hours of illumination. DNA sequences upstream of thecab-m7 gene resemble those found in the 5′-flanking regions of some other plant genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00029148
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