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  • 1
    Electronic Resource
    Electronic Resource
    Biopsy of Sentinel Node in Mammary Cancer: Initial Experience at the Centro Clinico de Estereotaxia, Caracas, Venezuela (2003)
    Oxford, UK : Blackwell Science Inc
    The @breast journal 9 (2003), S. 0 
    Details
    ISSN: 1524-4741
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1524-4741.2003.09625.x
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  • 2
    Electronic Resource
    Electronic Resource
    Transposition of the maize autonomous element Activator in transgenic Nicotiana plumbaginifolia plants (1993)
    Springer
    Molecular genetics and genomics 238 (1993), S. 209-217 
    Details
    ISSN: 1617-4623
    Keywords: Transposable element ; Ac ; Nicotiana plumbaginifolia ; Gene tagging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The maize autonomous transposable element Ac was introduced into haploid Nicotiana plumbaginifolia via Agrobacterium tumefaciens transformation of leaf disks. All the regenerated transformants (R0) were diploid and either homozygous or heterozygous for the hygromycin resistance gene used to select primary transformants. The Ac excision frequency was determined using the phenotypic assay of restoration of neomycin phosphotransferase activity and expression of kanamycin resistance among progeny seedlings. Some of the R0 plants segregated kanamycin-resistant seedlings in selfed progeny at a high frequency (34 to 100%) and contained one or more transposed Ac elements. In the primary transformants Ac transposition probably occurred during plant regeneration or early development. Other R0 transformants segregated kanamycin-resistant plants at a low frequency (≤ 4%). Two transformants of this latter class, containing a unique unexcised Ac element, were chosen for further study in the expectation that their kanamycin resistant progeny would result from independent germinal transposition events. Southern blot analysis of 32 kanamycin-resistant plants (R1 or R2), selected after respectively one or two selfings of these primary transformants, showed that 27 had a transposed Ac at a new location and 5 did not have any Ac element. Transposed Ac copy number varied from one to six and almost all transposition events were independent. Southern analysis of the R2 and R3 progeny of these kanamycin-resistant plants showed that Ac continued to transpose during four generations, and its activity increased with its copy number. The frequency of Ac transposition, from different loci, remained low (≤ 7%) from R0 to R3 generations when only one Ac copy was present. The strategy of choosing R0 plants that undergo a low frequency of germinal excision will provide a means to avoid screening non-independent transpositions and increase the efficiency of transposon tagging.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00279549
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  • 3
    Electronic Resource
    Electronic Resource
    Interest in and limits to the utilization of reporter genes for the analysis of transcriptional regulation of nitrate reductase (1992)
    Springer
    Molecular genetics and genomics 235 (1992), S. 259-268 
    Details
    ISSN: 1617-4623
    Keywords: Nitrate reductase ; Reporter gene ; Nicotiana tabacum ; Nicotiana plumbaginifolia ; Transgenic plant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Reporter gene techniques and mutant analysis were used to identify the molecular basis of the regulation of the expression of nitrate reductase (NR) by nitrate and nitrate-, or ammonium-derived metabolites (N-metabolites), in the true diploïd species Nicotiana plumbaginifolia and in the amphidiploïd species Nicotiana tabacum. The N. plumbaginifolia mutant E23 results from the insertion of a Tnt1-like retrotransposon (Tnp2) in the first exon of the single-copy nia gene, which encodes nitrate reductase. One of the resulting transcripts ends in the 5′ LTR (long terminal repeat) sequence of this retrotransposon, and another one in the 3′ LTR. Nitrate and N-metabolites modulate the expression of these truncated transcripts, indicating that intron splicing and termination processes are not essential to these regulatory events. A GUS reporter sequence was transcriptionally linked to the promoter of the nia-1 gene of N. tabacum. This fusion was functional in transient expression assays done with protoplasts derived from mesophyll cells of N. tabacum. However none of the regulatory mechanisms known to affect steady-state levels of the nia-1 transcript were operative under these experimental conditions. Transgenic plants carrying either this fusion or translational fusions of GUS linked to the promoter of either the nia-1 or nia-2 gene of N. tabacum were obtained by Agrobacterium-mediated transfer. A low proportion of the transgenic plants (22 out of 105 independent transformants) expressed GUS activity although at a low level. Only 4 plants exhibited a detectable level of GUS mRNA. The concentration of this mRNA increased significantly in an NR-deficient background, indicating regulation by N-metabolites. Only 2 plants, however, showed regulation (induction) by nitrate. Attempts to use aux2 or nptII reporter sequences linked to either the nia-1 or nia-2 promoter as marker genes for the selection of regulatory mutants of the nitrate assimilation pathway were unsuccessful because of our inability to isolate transgenic plants in which these reporter genes were properly regulated by nitrate. The implications of these results are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00279369
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  • 4
    Electronic Resource
    Electronic Resource
    Engineering seed dormancy by the modification of zeaxanthin epoxidase gene expression (1999)
    Springer
    Plant molecular biology 39 (1999), S. 1267-1274 
    Details
    ISSN: 1573-5028
    Keywords: abscisic acid ; Nicotiana plumbaginifolia ; seed ; dormancy ; germination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Abscisic acid (ABA) is a plant hormone synthesized during seed development that is involved in the induction of seed dormancy. Delayed germination due to seed dormancy allows long-term seed survival in soil but is generally undesirable in crop species. Freshly harvested seeds of wild-type Nicotiana plumbaginifolia plants exhibit a clear primary dormancy that results in delayed germination, the degree of primary dormancy being influenced by environmental culture conditions of the mother plant. In contrast, seeds, obtained either from ABA-deficient mutant aba2-s1 plants directly or aba2-s1 plants grafted onto wild-type plant stocks, exhibited rapid germination under all conditions irrespective of the mother plant culture conditions. The ABA biosynthesis gene ABA2 of N. plumbaginifolia, encoding zeaxanthin epoxidase, was placed under the control of the constitutive 35S promoter. Transgenic plants overexpressing ABA2 mRNA exhibited delayed germination and increased ABA levels in mature seeds. Expression of an antisense ABA2 mRNA, however, resulted in rapid seed germination and in a reduction of ABA abundance in transgenic seeds. It appears possible, therefore, that seed dormancy can be controlled in this Nicotiana model species by the manipulation of ABA levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006145025631
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