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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    ISSN: 0378-4371
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2242
    Keywords: B chromosomes ; Pollen mitosis ; Secale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Rye plants carrying B chromosomes with different nuclear and cytoplasmic constitutions have been analyzed at first pollen mitosis. No differences of B chromosome behaviour have been detected. It has been concluded that non-disjunction and preferential distribution are processes controlled by Bs themselves. At second pollen anaphase, B laggards have been observed. Both non-disjunction and B laggards occurred with higher frequency in younger anthers.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2242
    Keywords: B-chromosomes ; Cytoplasmatic-factor ; Homoeology ; Secale ; Translocations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The meiotic behaviour of hybrids between Secale cereale carrying B chromosomes and S. vavilovii has been studied in order to estimate the effects of B chromosomes on hybrid meiotic pairing. The possible effect of Bs on the meiotic pairing of the offspring from backcrosses with S. vavilovii has been studied also. The results obtained clearly indicate that no detectable differences existed in chromosome pairing of hybrids with or without B chromosomes. The hypothetical existence of epistatic genes on cereale genome masking the effect of Bs has been rejected after the results obtained in backcrosses. Therefore, lack of qualitative genes controlling interspecific pairing on rye B chromosomes has been concluded. A quantitative effect of B chromosomes was detected only when they were in alien cytoplasm.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0568
    Keywords: Key words Cardiac morphogenesis ; Slug ; Epicardium ; Cushion mesenchyme ; Epithelial-mesenchymal transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Slug is a transcription factor involved in processes such as the formation of mesoderm and neural crest, two developmental events that imply a transition from an epithelial to a mesenchymal phenotype. During late cardiac morphogenesis, mesenchymal cells originate from two epithelia – epicardial mesothelium and cushion endocardium. We aimed to check if Slug is expressed in these systems of epithelial-mesenchymal transition. We have immunolocated the Slug protein in the heart of quail embryos between Hamburger and Hamilton stages HH16 and HH30. In the proepicardium (the epicardial primordium), Slug was detected in most cells, mesothelial as well as mesenchymal. Slug immunoreactivity was strong in the mesenchyme of the endocardial cushions and subepicardium from its inception until HH24, but the immunoreactivity disappeared in later embryos. Only a small portion of the endocardial cells located in the areas of epithelial-mesenchymal transition (atrioventricular groove and outflow tract) were immunolabelled, mainly between HH16 and HH20. Endocardial cells from other cardiac segments were always negative, except for a transient, weak immunoreactivity that coincided with the development of the intertrabecular sinusoids of the ventricle. In contrast, virtually all cells of the epicardial mesothelium were immunoreactive until stage HH24. The mesenchymal cells that migrate to the heart through the spina vestibuli were also conspicuously immunoreactive. The myocardium was not labelled in the stages studied. Our results stress the involvement of Slug in the epithelial to mesenchymal transition. We suggest that Slug can constitute a reliable marker of the cardiac epithelial cells that are competent to transform into mesenchyme as well as a transient marker of the epithelial-derived mesenchymal cells in the developing heart.
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  • 5
    ISSN: 1432-0916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract By using Agmon's geodesic ideas to single out particular regions in path space, we obtain optimal lower bounds on the leading behavior for the fall off of the ground state of multiparticle system.
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  • 6
    ISSN: 1432-0916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract We prove that the Schrödinger operatorH=−d 2/dx 2+V(x)+F·x has purely absolutely continuous spectrum for arbitrary constant external fieldF, for a large class of potentials; this result applies to many periodic, almost periodic and random potentials and in particular to random wells of independent depth for which we prove that whenF=0, the spectrum is almost surely pure point with exponentially decaying eigenfunctions.
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  • 7
    ISSN: 1617-4623
    Keywords: Key words Evolutionary gene transfer ; Plant mitochondria ; Ribosomal protein S14 ; Mitochondrial targeting peptide ; Nuclear intron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The transfer of genetic information from the mitochondrion to the nucleus is thought to be still underway in higher plants. The mitochondrial genome of Arabidopsis thaliana contains only one rps14 pseudogene. In this paper we show that the functional gene encoding mitochondrial ribosomal protein S14 has been translocated to the nucleus. This gene transfer is a recent evolutionary event, which occurred within Cruciferae, probably after the divergence of Arabidopsis and Brassica napus. A 5′ extension of the rps14 reading frame encodes a presequence which, in vitro, targets the polypeptide to isolated mitochondria and is cleaved off during or after import. No intron was found at the junction of the targeting presequence with the mitochondrially derived sequence, which are directly connected. By contrast, a 90-bp intron, which is removed by splicing to give a mature poly(A)+mRNA of 0.9 kb, is located in the 3′ non-coding region. To our knowledge, this is the first report of an intron in such a position in a functional transferred gene in higher plants, and suggests that exon shuffling may have been involved in the acquisition of elements necessary for expression in the nucleus. Putative roles of this intron in polyadenylation and enhancement of gene expression are discussed.
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  • 8
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Modifications in the chloride (mitochondria-rich) and pavement cells of the gill epithelia of the Adriatic sturgeon Acipenser naccarii after their transfer under hypertonic environmental conditions (salinity 35) were examined by light and electron microscopy. In contrast to freshwater specimens, seawater-acclimated fish showed a marked increase in the number and size of chloride cells. Ultrastructural modifications included: presence of a slightly invaginated apical crypt, a darker cytoplasm, a more compact tubular system, a major increase in cisternae from Golgi apparatus stacks and flattened-out sacs with dilated ends that produced an increase in lateral and basal cell surfaces. All these changes indicated enhanced cellular activity. Pavement cells, which largely covered the chloride cells on the gill filament and lamella, exhibited a complex system of microridges on their apical surface. Typical features included numerous desmosomes that characterized the intercellular junction, and the presence in the apical cytoplasm of bundles of filaments and of electro-dense vesicles in freshwater fish or clear vesicles in seawater-acclimated animals.
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  • 9
    ISSN: 1432-2242
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary To contribute to knowledge on the significance of B chromosomes in rye populations, a component of fertility has been estimated by a comparative study of germination and growth of pollen tubes in plants with and without B chromosomes. The highest percentage germination of pollen and mean speed of pollen tube growth was shown by 14 + 2B plants, followed by normal plants. Observations of first pollen mitosis indicated that in most cases the chromatid constitution of the tube nucleus was the same in 14, 14 + 1 and 14 + 2B plants. In contrast, the mean growth rate of pollen tubes differed significantly among the three cases. From these data it seems that the determination of germination ability and pollen tube growth depends on the sporophyte and is related to the number of Bs carried by the plant.
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  • 10
    ISSN: 1432-2064
    Keywords: 60H25
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary This paper is devoted to the analysis of the large time behavior of the solutions of the Anderson parabolic problem: $$\frac{{\partial u}}{{\partial t}} = \kappa \Delta u\xi (x)u$$ when the potential ξ(x) is a homogeneous ergodic random field on ℝ d . Our goal is to prove the asymptotic spatial intermittency of the solution and for this reason, we analyze the large time properties of all the moments of the positive solutions. This provides an extension to the continuous space ℝ d of the work done originally by Gärtner and Molchanov in the case of the lattice ℤ d . In the process of our moment analysis, we show that it is possible to exhibit new asymptotic regimes by considering a special class of generalized Gaussian fields, interpolating continuously between the exponent 2 which is found in the case of bona fide continuous Gaussian fields ξ(x) and the exponent 3/2 appearing in the case of a one dimensional white noise. Finally, we also determine the precise almost sure large time asymptotics of the positive solutions.
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