References of "Deltour, Roger"
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See detailThe Frequency of Plasmodesmata Increases Early in the Whole Shoot Apical Meristem of Sinapis Alba L. During Floral Transition
Ormenese, Sandra ULg; Havelange, Andrée ULg; Deltour, Roger ULg et al

in Planta (2000), 211(3), 370-5

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 ... [more ▼]

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. [less ▲]

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See detailElectrical and dielectric properties of carbon black filled co-continuous two-phase polymer blends
Calberg, Cédric ULg; Blacher, Silvia ULg; Gubbels, F. et al

in Journal of Physics D - Applied Physics (1999), 32(13), 1517-1525

The electrical and dielectric properties of co-continuous polystyrene (PS)/ρoly(methylmethacrylate)(PMMA) blends loaded with carbon black (CB) of a special grade (BP 1000) have been studied. They strongly ... [more ▼]

The electrical and dielectric properties of co-continuous polystyrene (PS)/ρoly(methylmethacrylate)(PMMA) blends loaded with carbon black (CB) of a special grade (BP 1000) have been studied. They strongly depend on the selective localization of the CB particles at the blend interface quite consistently with the double percolation concept. The interfacial localization of CB contributes to the stabilization of the phase morphology against thermal post treatment. Nevertheless, the sample annealing has a very favourable effect on the percolation threshold that decreases The composition range in which phases are co-continuous is also increased by the addition of the filler. Dispersion of the conductance and the dielectric constant has been measured in the wide frequency range 10-4-108 Hz for blends containing 0-5 wt% CB. On the basis of these results, the mechanism of electrical transport (trapping, hopping, tunnelling, percolation) has been discussed in relation to the CB loading and the optimum loading has been identified for the electrical and dielectric properties to be stable and reproducible [less ▲]

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See detailUltrastructural distribution of DNA within plant meristematic cell nucleoli during activation and the subsequent inactivation by a cold stress.
Mineur, Pierre ULg; Jennane, A.; Thiry, Marc ULg et al

in Journal of Structural Biology (1998), 123(3), 199-210

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 ... [more ▼]

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. [less ▲]

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See detailThree-dimensional electron microscopy of ribosomal chromatin in two higher plants: a cytochemical, immunocytochemical, and in situ hybridization approach.
Motte, Patrick ULg; Loppes, Roland ULg; Menager, M. et al

in Journal of Histochemistry and Cytochemistry : Official Journal of the Histochemistry Society (1991), 39(11), 1495-506

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 ... [more ▼]

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. [less ▲]

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See detailThe Nucleolonema of Plant and Animal Cells: A Comparison
Deltour, Roger ULg; Motte, Patrick ULg

in Biology of the Cell (1990), 68(1), 5-11

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 ... [more ▼]

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. [less ▲]

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