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R Deltour

Publications and source records attributed to R Deltour.

At least 19 recordsLinked to original sources
PubMed2000

Coulomb-Gas scaling law for a superconducting Bi(2+y)Sr(2-x-y)La(x)CuO(6+delta) thin films in magnetic fields

The electrical transport properties of epitaxial superconducting Bi(2+y)Sr(2-x-y)La(x)CuO(6+delta) thin films have been studied in magnetic fields. Using a modified Coulomb-gas scaling law, we can fit all the magnetic field dependent low resistance data with a universal scaling curve, which allows us to determine a relation between the activation energy of the thermally activated flux flow resistance and the characteristic temperature scaling parameters.

Journal Article↗
PubMed2000

The frequency of plasmodesmata increases early in the whole shoot apical meristem of Sinapis alba L. during floral transition.

The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1, L2, L3) as well as at the interfaces between these layers, and it occurs in both the central and peripheral zones of the shoot apical meristem. The extra plasmodesmata are formed only transiently, from 28 to 48 h after the start of the long day, and acropetally since they are detectable in L3 4 h before they are seen in L1 and L2. These observations indicate that (i) in the Sinapis shoot apical meristem at floral transition, there is an unfolding of a single field with increased plasmodesmatal connectivity, and (ii) this event is an early effect of the arrival at this meristem of the floral stimulus of leaf origin. Since (i) the wave of increased frequency of plasmodesmata is 12 h later than the wave of increased mitotic frequency (A. Jacqmard et al. 1998, Plant cell proliferation and its regulation in growth and development, pp. 67 78; Wiley), and (ii) the increase in frequency of plasmodesmata is observed in all cell walls, including in walls not deriving from recent divisions (periclinal walls separating the cell layers), it is concluded that the extra plasmodesmata seen at floral transition do not arise in the forming cell plate during mitosis and are thus of secondary origin.

Meristem↗
PubMed1998

Ultrastructural distribution of DNA within plant meristematic cell nucleoli during activation and the subsequent inactivation by a cold stress.

We have investigated the precise location of DNA within the meristematic cell nucleolus of Zea mays root cells and Pisum sativum cotyledonary buds, in the course of their activation and induced inactivation following a subsequent treatment at low temperature. For this purpose, we combined the acetylation method, providing an excellent distinction between the various nucleolar components, with the in situ terminal deoxynucleotidyl transferase-immunogold technique, a highly sensitive method for detecting DNA at the ultrastructural level. In addition to the presence of DNA in the condensed chromatin associated with the nucleolus, we demonstrated that a significant label was detected in the nucleolus of quiescent cells in both plant models. Evident labels were also found in the dense fibrillar component of actived nucleoli. Whereas in inactivated nucleoli no significant label was observed within the dense fibrillar component, an intense label was seen over the large heterogeneous fibrillar centres only during inactivation. The granular component was never significantly labelled. These results appear to indicate that the DNA present in the dense fibrillar component of activated nucleoli withdraws from this structure during its inactivation and becomes incorporated in the large fibrillar centres. These observations suggest that in plant cells inactivation of rRNA genes is clearly accompanied by changes in the conformation of ribosomal chromatin.

Cell Nucleolus↗
PubMed1991

Three-dimensional electron microscopy of ribosomal chromatin in two higher plants: a cytochemical, immunocytochemical, and in situ hybridization approach.

We report the 3-D arrangement of DNA within the nucleolar subcomponents from two evolutionary distant higher plants, Zea mays and Sinapis alba. These species are particularly convenient to study the spatial organization of plant intranucleolar DNA, since their nucleoli have been previously reconstructed in 3-D from serial ultra-thin sections. We used the osmium ammine-B complex (a specific DNA stain) on thick sections of Lowicryl-embedded root fragments. Immunocytochemical techniques using anti-DNA antibodies and rDNA/rDNA in situ hybridization were also applied on ultra-thin sections. We showed on tilted images that the OA-B stains DNA throughout the whole thickness of the section. In addition, very low quantities of cytoplasmic DNA were stained by this complex, which is now the best DNA stain used in electron microscopy. Within the nucleoli the DNA was localized in the fibrillar centers, where large clumps of dense chromatin were also visible. In the two plant species intranucleolar chromatin forms a complex network with strands partially linked to chromosomal nucleolar-organizing regions identified by in situ hybridization. This study describes for the first time the spatial arrangement of the intranucleolar chromatin in nucleoli of higher plants using high-resolution techniques.

Chromatin↗
PubMed1990

The nucleolonema of plant and animal cells: a comparison.

Depending on the author and the animal or plant origin of the material under study, the term "nucleolonema" is used in different contexts and thus indicates nucleolar ultrastructures that are different. In this paper, we attempt to clarify this state of affairs and to propose a definition for the plant cell nucleolonema.

Animals↗
PubMed1986

Three-dimensional electron microscopy of the internal nucleolus-associated chromatin and of the nucleolar vacuoles during early germination of Sinapis alba.

Spatial relationships between the internal nucleolus-associated chromatin (NAC) and the numerous nucleolar vacuoles that appear during early germination have been studied in nucleoli of quiescent (non-germinated) and early germinating embryos of Sinapis using serial sections. In quiescent non-vacuolated nucleoli, the transcriptionally inactive internal NAC is a short strand about 900 nm thick that in cross-section appears as heterogeneous fibrillar centres (FCs). At 4 and 6 h after germination one or several large networks of interconnected nucleolar vacuoles develop around the dispersing internal NAC. Clumps of dense chromatin are still present within the nucleolar vacuoles and are probably unfolding into deoxyribonucleoprotein (DNP) fibres (about 110 nm thick), which rapidly intrude within the nucleolar body and form thin chromatin threads. At 24 h after germination the internal NAC is more dispersed and forms, for its greatest part, a long thread (about 240 nm in diameter) wrapped up with a few dense fibrillar component, the whole forming the first outline of a nucleolonema. In cross-section most of the internal NAC appears as homogeneous FCs but short portions remain more condensed and appear as heterogeneous FCs always associated with a nucleolar vacuole. From 48 h the internal NAC is a longer thinner strand (about 160 nm in diameter), probably continuous and surrounded entirely by a homogeneous muff of dense fibrillar component, the whole forming a typical nucleolonema (about 950 nm thick) meandering throughout the nucleolus. Small amounts of the internal NAC still remain undispersed in the form of heterogeneous FCs associated with a nucleolar vacuole. The repeated association of nucleolar vacuoles and dispersing internal NAC suggests that they could play a role in chromatin dispersion and, or, activation by creating a favourable microenvironment.

Cell Nucleolus↗
PubMed1985

Nucleolar activation and vacuolation in embryo radicle cells during early germination.

The activation of the nucleolus of primary root cells of Sinapis alba embryos during the first 72 h of germination was monitored by autoradiographic, ultrastructural and microstereological methods. Autoradiographs showed that within 48 h, the nucleolus progressively resumed the capacity to synthesize pre-rRNA molecules at a high rate. In quiescent embryos the nucleolus was small, compact and composed of mixed granular and fibrillar components. Within the first 6 h of germination a strong nucleolar vacuolation occurred, accompanied by a decrease in the volume of the nucleolus and a concomitant high loss of its ribonucleoproteins (RNPs). From 6 to 24 h, nucleolar vacuolation decreased to reach a stable level. During this last period the volume of the nucleolus increased by the accumulation of the fibrillar component resulting from a slow pre-rRNA processing. At 24 h the nucleolus presented a predominantly fibrillar texture. After 24 h, nucleolus growth continued but was due to the accumulation of the granular component, indicating that pre-rRNA processing occurred at a higher rate than during the first day of germination. From 48 h the nucleolus was composed of well-delineated granular and fibrillar areas. Dense nucleolus-associated chromatin as well as fibrillar centres were always observed during the whole period of observation. In addition, previous studies on the nucleolus of radicle cells of Zea mays embryo during early germination were completed by studying changes in the nucleolar volume and in the density of pre-ribosomal subunits of the granular component. On the basis of the data obtained with both species we suggest that a possible function for the nucleolar vacuoles is the increase in the nucleolus-nucleoplasm exchange interface in response to a rapid increase in the output of nucleolar RNPs. The nucleolar growth pattern during early germination is also discussed.

Autoradiography↗