References of "Ormenese, Sandra"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailImpaired angiogenesis and tumor development by inhibition of the mitotic kinesin Eg5.
Exertier, Prisca; Javerzat, Sophie; Wang, Baigang et al

in Oncotarget (2013), 4(12), 2302-16

Kinesin motor proteins exert essential cellular functions in all eukaryotes. They control mitosis, migration and intracellular transport through interaction with microtubules. Small molecule inhibitors of ... [more ▼]

Kinesin motor proteins exert essential cellular functions in all eukaryotes. They control mitosis, migration and intracellular transport through interaction with microtubules. Small molecule inhibitors of the mitotic kinesin KiF11/Eg5 are a promising new class of anti-neoplastic agents currently evaluated in clinical cancer trials for solid tumors and hematological malignancies. Here we report induction of Eg5 and four other mitotic kinesins including KIF20A/Mklp2 upon stimulation of in vivo angiogenesis with vascular endothelial growth factor-A (VEGF-A). Expression analyses indicate up-regulation of several kinesin-encoding genes predominantly in lymphoblasts and endothelial cells. Chemical blockade of Eg5 inhibits endothelial cell proliferation and migration in vitro. Mitosis-independent vascular outgrowth in aortic ring cultures is strongly impaired after Eg5 or Mklp2 protein inhibition. In vivo, interfering with KIF11/Eg5 function causes developmental and vascular defects in zebrafish and chick embryos and potent inhibition of tumor angiogenesis in experimental tumor models. Besides blocking tumor cell proliferation, impairing endothelial function is a novel mechanism of action of kinesin inhibitors. [less ▲]

Detailed reference viewed: 5 (0 ULg)
Full Text
Peer Reviewed
See detailMatrix metalloproteinase-2 governs lymphatic vessel formation as an interstitial collagenase.
Detry, Benoît ULg; Erpicum, Charlotte ULg; Paupert, Jenny ULg et al

in Blood (2012), 119(21), 5048-56

Lymphatic dysfunctions are associated with several human diseases, including lymphedema and metastatic spread of cancer. Although it is well recognized that lymphatic capillaries attach directly to ... [more ▼]

Lymphatic dysfunctions are associated with several human diseases, including lymphedema and metastatic spread of cancer. Although it is well recognized that lymphatic capillaries attach directly to interstitial matrix mainly composed of fibrillar type I collagen, the interactions occurring between lymphatics and their surrounding matrix have been overlooked. In this study, we demonstrate how matrix metalloproteinase (MMP)–2 drives lymphatic morphogenesis through Mmp2-gene ablation in mice, mmp2 knockdown in zebrafish and in 3D-culture systems, and through MMP2 inhibition. In all models used in vivo (3 murine models and thoracic duct development in zebrafish) and in vitro (lymphatic ring and spheroid assays), MMP2 blockage or down-regulation leads to reduced lymphangiogenesis or altered vessel branching. Our data show that lymphatic endothelial cell (LEC) migration through collagen fibers is affected by physical matrix constraints (matrix composition, density and cross-linking). Transmission electron microscopy (TEM) and confocal reflection microscopy using DQ-collagen highlight the contribution of MMP2 to mesenchymal-like migration of LEC associated with collagen fiber remodeling. Our findings provide new mechanistic insight into how LEC negotiate an interstitial type I collagen barrier and reveal an unexpected MMP2-driven collagenolytic pathway for lymphatic vessel formation and morphogenesis. [less ▲]

Detailed reference viewed: 147 (63 ULg)
Full Text
Peer Reviewed
See detailWhat is the Contribution of Host-Derived CMV Immunity after Allogeneic Transplantation following Non-Myeloablative Conditioning?
MENTEN, Catherine ULg; Castermans, E.; Hannon, Muriel ULg et al

in Haematologica (2012), 97(Supplement 1), 720

Detailed reference viewed: 10 (5 ULg)
Full Text
See detailEvidence for Expansion of Host-derived CMV-specific CD8+ T cells after Allogeneic Transplantation with Non-Myeloablative Conditioning
MENTEN, Catherine ULg; Castermans, E.; Hannon, Muriel ULg et al

in Belgian Journal of Hematology (2012), Abstracts book(Supplement of 27th General Meeting of the Belgian Hematological Society), 16

Detailed reference viewed: 3 (1 ULg)
Full Text
Peer Reviewed
See detailInduction of the Alternative NF-{kappa}B Pathway by Lymphotoxin {alpha}{beta} (LT{alpha}{beta}) Relies on Internalization of LT{beta} Receptor
Ganeff, Corine; Remouchamps, Caroline ULg; Boutaffala, Layla et al

in Molecular & Cellular Biology (2011), 21

Several tumor necrosis factor receptor (TNFR) family members activate both the classical and the alternative NF-κB pathways. However, how a single receptor engages these two distinct pathways is still ... [more ▼]

Several tumor necrosis factor receptor (TNFR) family members activate both the classical and the alternative NF-κB pathways. However, how a single receptor engages these two distinct pathways is still poorly understood. Using lymphotoxin β receptor (LTβR) as a prototype, we showed that activation of the alternative, but not the classical, NF-κB pathway relied on internalization of the receptor. Further molecular analyses revealed a specific cytosolic region of LTβR essential for its internalization, TRAF3 recruitment, and p100 processing. Interestingly, we found that dynamin-dependent, but clathrin-independent, internalization of LTβR appeared to be required for the activation of the alternative, but not the classical, NF-κB pathway. In vivo, ligand-induced internalization of LTβR in mesenteric lymph node stromal cells correlated with induction of alternative NF-κB target genes. Thus, our data shed light on LTβR cellular trafficking as a process required for specific biological functions of NF-κB. [less ▲]

Detailed reference viewed: 57 (14 ULg)
Peer Reviewed
See detailLymphangiogenesis and extracellular matrix remodeling
Erpicum, Charlotte ULg; Detry, Benoît ULg; Paupert, Jenny ULg et al

Poster (2011)

Lymphangiogenesis, the formation of new lymphatic vessels from preexisting ones, is an important biological process associated with diverse pathologies, such as metastatic dissemination and graft ... [more ▼]

Lymphangiogenesis, the formation of new lymphatic vessels from preexisting ones, is an important biological process associated with diverse pathologies, such as metastatic dissemination and graft rejection. Our laboratory has previously identified MMP2 as a key regulator of lymphangiogenesis in vitro and in vivo. However, the exact function of MMP2 in this process is yet unknown. The present work aims at elucidating the mechanisms of MMP2 action during lymphangiogenesis. MMP2 could either act as a growth factor activator or as a regulator of matrix remodeling. To address this question, we studied the effect of MMP2 on lymphangiogenesis in an novel in vitro model of sprouting cells from small aggregates (spheroids) seeded in a collagen gel. In this model, quantification of the lymphangiogenic response is performed through computerized methods allowing the measurement of the distance of migration, but also the evaluation of how the cell are migrating. We evaluated the impact of MMP2 blockage through the use of physiological (TIMP2) or chemical inhibitors or by downregulating its expression with specific siRNA. The importance of extracellular matrix composition is evaluated by embedding these spheroids into different matrices (matrigel versus collagen; pepsinized collagen versus native collagen; different collagen concentrations). Our results reveal a modification of cell migration through collagen gel after MMP2 inhibition. The utilization of DQ collagen and microscopy refractance confirmed the importance of MMP2 collagenoyitic activity for lymphangiogenesis. [less ▲]

Detailed reference viewed: 12 (1 ULg)
Full Text
Peer Reviewed
See detailCytokinin promotes flowering of Arabidopsis via transcriptional activation of the FT paralogue TSF
D'Aloia, Maria ULg; Bonhomme, Delphine ULg; Bouché, Frédéric ULg et al

in Plant Journal (The) (2011), 65

Cytokinins are involved in many aspects of plant growth and development and physiological evidence also indicates that they have a role in floral transition. In order to integrate these phytohormones into ... [more ▼]

Cytokinins are involved in many aspects of plant growth and development and physiological evidence also indicates that they have a role in floral transition. In order to integrate these phytohormones into the current knowledge of genetically defined molecular pathways to flowering, we performed exogenous treatments of adult wild-type and mutant Arabidopsis plants and analysed the expression of candidate genes. We used a hydroponic system that enables synchronous growth and flowering of Arabidopsis and allows precise application of chemicals to the roots for defined periods of time. We show that application of N6-benzylaminopurine (BAP) promotes flowering of plants grown in non-inductive short days. The response to cytokinin treatment does not require FLOWERING LOCUS T (FT) but activates its paralogue TWIN SISTER OF FT (TSF), as well as FD, which encodes a partner protein of TSF, and the downstream gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1). Treatment of selected mutants confirmed that TSF and SOC1 are necessary for the flowering response to BAP while the activation cascade might partially act independently of FD. These experiments provide a mechanistic basis for the role of cytokinins in flowering and demonstrate that the redundant genes FT and TSF are differently regulated by distinct floral inducing signals. [less ▲]

Detailed reference viewed: 40 (16 ULg)
Full Text
Peer Reviewed
See detailDentin Matrix Protein 1 induces membrane expression of VE-cadherin on endothelial cells and inhibits VEGF-induced angiogenesis by blocking VEGFR-2 phosphorylation.
Pirotte, Sophie ULg; Lamour, Virginie ULg; Lambert, Vincent ULg et al

in Blood (2011), 117(8), 2515-26

Dentin matrix protein 1 (DMP1) is a member of the Small Integrin-Binding LIgand N-linked Glycoproteins (SIBLINGs) family, a group of proteins initially described as mineralized extracellular matrices ... [more ▼]

Dentin matrix protein 1 (DMP1) is a member of the Small Integrin-Binding LIgand N-linked Glycoproteins (SIBLINGs) family, a group of proteins initially described as mineralized extracellular matrices components. More recently, SIBLINGs have been implicated in several key steps of cancer progression, including angiogenesis. Although pro-angiogenic activities have been demonstrated for two SIBLINGs, the role of DMP1 in angiogenesis has not been addressed yet. We demonstrated that this extracellular matrix protein induced the expression of VE-cadherin, a key regulator of intercellular junctions and contact inhibition of growth of endothelial cells that is also known to modulate VEGFR-2 activity, the major high affinity receptor for VEGF. DMP1 induced VE-cadherin and p27(Kip1) expression followed by cell cycle arrest in human umbilical vein endothelial cells (HUVEC) in a CD44-dependent manner. VEGF-induced proliferation, migration and tubulogenesis responses were specifically blocked upon DMP1 pre-treatment of HUVEC. Indeed, subsequently to VE-cadherin induction, DMP1 inhibited VEGFR-2 phosphorylation and Src-mediated signaling. However, DMP1 did not interfere with bFGF-induced angiogenesis. In vivo, DMP1 significantly reduced laser-induced choroidal neovascularization lesions and tumor-associated angiogenesis. These data enable us to put DMP1 on the angiogenic chessboard for the first time and to identify this protein as a new specific inhibitor of VEGF-induced angiogenesis. [less ▲]

Detailed reference viewed: 163 (41 ULg)
Full Text
Peer Reviewed
See detailElongator controls the migration and differentiation of cortical neurons through acetylation of a tubulin
Creppe, Catherine ULg; Malinouskaya, Lina ULg; Volvert, Marie-Laure ULg et al

in Cell (2009), 136

The generation of cortical projection neurons relies on the coordination of radial migration with branching. Here we report that the multi-subunit histone acetyltransferase Elongator complex, which ... [more ▼]

The generation of cortical projection neurons relies on the coordination of radial migration with branching. Here we report that the multi-subunit histone acetyltransferase Elongator complex, which contributes to transcript elongation, also regulates the maturation of projection neurons. Indeed, silencing of its scaffold (Elp1) or catalytic subunit (Elp3) cell-autonomously delays the migration and impairs the branching of projection neurons. Strikingly, neurons defective in Elongator show reduced levels of acetylated alpha tubulin. A direct reduction of alpha tubulin acetylation leads to comparable defects in cortical neurons and suggests that alpha tubulin is a target of Elp3. This is further supported by the demonstration that Elp3 promotes acetylation and counteracts HDAC6-mediated deacetylation of this substrate in vitro. Our results uncover alpha tubulin as a target of the Elongator complex and suggest that a tight regulation of its acetylation underlies the maturation of cortical projection neurons. [less ▲]

Detailed reference viewed: 260 (97 ULg)
Full Text
Peer Reviewed
See detailWhat Is The Role For Regulatory T-Cells After Nonmyeloablative Conditioning?
Humblet-Baron, S.; CASTERMANS, Emilie ULg; Vanbellinghen, J.-F. et al

in Biology of Blood & Marrow Transplantation (2009, February), 15(2), 122-123

Detailed reference viewed: 11 (3 ULg)
Full Text
Peer Reviewed
See detailA Temperature-sensitive mutation in the Arabidopsis thaliana phosphomannomutase gene disrupts protein glycosylation and triggers cell death.
Hoeberichts, Frank A; Vaeck, Elke; Kiddle, Guy et al

in Journal of Biological Chemistry (2008), 283(9), 5708-18

Eukaryotic phosphomannomutases (PMMs) catalyze the interconversion of mannose 6-phosphate to mannose 1-phosphate and are essential to the biosynthesis of GDP-mannose. As such, plant PMMs are involved in ... [more ▼]

Eukaryotic phosphomannomutases (PMMs) catalyze the interconversion of mannose 6-phosphate to mannose 1-phosphate and are essential to the biosynthesis of GDP-mannose. As such, plant PMMs are involved in ascorbic acid (AsA) biosynthesis and N-glycosylation. We report on the conditional phenotype of the temperature-sensitive Arabidopsis thaliana pmm-12 mutant. Mutant seedlings were phenotypically similar to wild type seedlings when grown at 16-18 degrees C but died within several days after transfer to 28 degrees C. This phenotype was observed throughout both vegetative and reproductive development. Protein extracts derived from pmm-12 plants had lower PMM protein and enzyme activity levels. In vitro biochemical analysis of recombinant proteins showed that the mutant PMM protein was compromised in its catalytic efficiency (K cat/K m). Despite significantly decreased AsA levels in pmm-12 plants, AsA deficiency could not account for the observed phenotype. Since, at restrictive temperature, total glycoprotein patterns were altered and glycosylation of protein-disulfide isomerase was perturbed, we propose that a deficiency in protein glycosylation is responsible for the observed cell death phenotype. [less ▲]

Detailed reference viewed: 56 (5 ULg)
Full Text
Peer Reviewed
See detailRevisiting the involvement of SELF-PRUNING in the sympodial growth of tomato.
Thouet, Johanna ULg; Quinet, Muriel; Ormenese, Sandra ULg et al

in Plant Physiology (2008), 148(1), 61-4

Detailed reference viewed: 20 (8 ULg)
Full Text
Peer Reviewed
See detailGenetical control of sympodial growth and flowering in tomato
Thouet, Johanna ULg; Ormenese, Sandra ULg; Périlleux, Claire ULg

in Comparative Biochemistry & Physiology Part A : Molecular & Integrative Physiology (2006), 143(4), 170-171

Detailed reference viewed: 34 (8 ULg)
Full Text
Peer Reviewed
See detailCytokinin application to the shoot apical meristem of Sinapis alba enhances secondary plasmodesmata formation.
Ormenese, Sandra ULg; Bernier, Georges ULg; Périlleux, Claire ULg

in Planta (2006), 224(6), 1481-4

A single application of cytokinin benzyladenine causes a threefold increase in the frequency of plasmodesmata in the vegetative shoot apical meristem (SAM) of Sinapis alba plants. This increase is ... [more ▼]

A single application of cytokinin benzyladenine causes a threefold increase in the frequency of plasmodesmata in the vegetative shoot apical meristem (SAM) of Sinapis alba plants. This increase is observed 20 h after application within all cell layers (L1, L2, L3) as well as at the interfaces between these layers. Evidence is presented indicating that cytokinin promotes mainly the formation of new secondary plasmodesmata. A similar increase in the frequency of secondary plasmodesmata was observed in the Sinapis SAM during the floral transition induced by a single long day, suggesting that this effect of the long day is mediated by cytokinin. [less ▲]

Detailed reference viewed: 20 (4 ULg)
Full Text
Peer Reviewed
See detailAcclimation of Arabidopsis thaliana to long-term CO2 enrichment and nitrogen supply is basically a matter of growth rate adjustment
Tocquin, Pierre ULg; Ormenese, Sandra ULg; Pieltain, Alexandra ULg et al

in Physiologia Plantarum (2006), 128(4), 677-688

The long-term response of Arabidopsis thaliana to increasing CO2 was evaluated in plants grown in 800 mu l 1(-1) CO2 from sowing and maintained, in hydroponics, on three nitrogen supplies: "low," "medium ... [more ▼]

The long-term response of Arabidopsis thaliana to increasing CO2 was evaluated in plants grown in 800 mu l 1(-1) CO2 from sowing and maintained, in hydroponics, on three nitrogen supplies: "low," "medium" and "high." The global response to high CO2 and N-supply was evaluated by measuring growth parameters in parallel with photosynthetic activity, leaf carbohydrates, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) messenger RNA and protein, stomatal conductance (g(s)) and density. CO2 enrichment was found to stimulate biomass production, whatever the N-supply. This stimulation was transient on low N-supply and persisted throughout the whole vegetative growth only in high N-supply. Acclimation on low N-high CO2 was not associated with carbohydrate accumulation or with a strong reduction in Rubisco amount or activity. At high N-supply, growth stimulation by high CO2 was mainly because of the acceleration of leaf production and expansion while other parameters such as specific leaf area, root/shoot ratio and g, appeared to be correlated with total leaf area. Our results thus suggest that, in strictly controlled and stable growing conditions, acclimation of A. thaliana to longterm CO2 enrichment is mostly controlled by growth rate adjustment. [less ▲]

Detailed reference viewed: 64 (10 ULg)
Full Text
Peer Reviewed
See detailAnalysis of the spatial expression pattern of seven kip related proteins (KRPs) in the shoot apex of Arabidopsis thaliana
Ormenese, Sandra ULg; de Almeida Engler, J.; De Groodt, R. et al

in Annals of Botany (2004), 93(5), 575-580

Background and aims Kip-related-proteins (KRPs), negative regulators of cell division, have recently been discovered in plants but their in planta function is as yet unclear. In this study the spatial ... [more ▼]

Background and aims Kip-related-proteins (KRPs), negative regulators of cell division, have recently been discovered in plants but their in planta function is as yet unclear. In this study the spatial expression of all seven KRP genes in shoot apices of Arabidopsis thaliana were compared. Methods In situ hybridization analyses were performed on longitudinal sections of shoot apices from 2-month-old Arabidopsis plants. Key Results The study provides evidence for different expression pattern groups. KRP1 and KRP2 expression is restricted to the endoreduplicating tissues. In contrast, KRP4 and KRP5 expression is mainly restricted to mitotically dividing cells. KRP3, KRP6 and KRP7 can be found in both mitotically dividing and endoreduplicating cells. Conclusion The results suggest differential roles for the distinct KRPs. KRP1 and KRP2 might specifically be involved in the establishment of polyploidy. In contrast, KRP4 and KRP5 might be involved in regulating the progression through the mitotic cell cycle. KRP3, KRP6 and KRP7 might have a function in both types of cell cycle. (C) 2004 Annals of Botany Company. [less ▲]

Detailed reference viewed: 23 (1 ULg)
Full Text
Peer Reviewed
See detailMicroarray analysis of E2Fa-DPa-overexpressing plants uncovers a cross-talking genetic network between DNA replication and nitrogen assimilation
Vlieghe, Kobe; Vuylsteke, Marnik; Florquin, Kobe et al

in Journal of Cell Science (2003), 116(20), 4249-4259

dPreviously we have shown that overexpression of the heterodimeric E2Fa-DPa transcription factor in Arabidopsis thaliana results in ectopic cell division, increased endoreduplication, and an early arrest ... [more ▼]

dPreviously we have shown that overexpression of the heterodimeric E2Fa-DPa transcription factor in Arabidopsis thaliana results in ectopic cell division, increased endoreduplication, and an early arrest in development. To gain a better insight into the phenotypic behavior of E2Fa-DPa transgenic plants and to identify E2Fa-DPa target genes, a transcriptomic microarray analysis was performed. Out of 4,390 unique genes, a total of 188 had a twofold or more up- (84) or down-regulated (104) expression level in E2Fa-DPa transgenic plants compared to wild-type lines. Detailed promoter analysis allowed the identification of novel E2Fa-DPa target genes, mainly involved in DNA replication. Secondarily induced genes encoded proteins involved in cell wall biosynthesis, transcription and signal transduction or had an unknown function. A large number of metabolic genes were modified as well, among which, surprisingly, many genes were involved in nitrate assimilation. Our data suggest that the growth arrest observed upon E2Fa-DPa overexpression results at least partly from a nitrogen drain to the nucleotide synthesis pathway, causing decreased synthesis of other nitrogen compounds, such as amino acids and storage proteins. [less ▲]

Detailed reference viewed: 24 (6 ULg)
Full Text
Peer Reviewed
See detailThe shoot apical meristem of Sinapis alba L. expands its central symplasmic field during the floral transition
Ormenese, Sandra ULg; Havelange, Andrée ULg; Bernier, Georges ULg et al

in Planta (2002), 215(1), 67-78

The shoot apical meristem (SAM) is functionally subdivided into zones with distinct tasks. During vegetative growth the peripheral zone of the meristem gives rise to leaf primordia that develop into ... [more ▼]

The shoot apical meristem (SAM) is functionally subdivided into zones with distinct tasks. During vegetative growth the peripheral zone of the meristem gives rise to leaf primordia that develop into dorsiventral leaves under the influence of signals from the central zone. During the floral transition the function of the SAM is altered and its peripheral zone starts to form floral structures in a specific pattern. This requires alterations in the signal networks that coordinate the activities of the peripheral and central zone of the SAM. These signal networks are partly housed in the symplasmic space of the SAM. Dye-coupling experiments demonstrate that in the superficial layer of the Sinapis alba meristem this space is radially subdivided. The cells of the central zone are coupled into a symplasmic field, which is shielded from the peripheral zone by the positional closing of plasmodesmata. In the vegetative meristems, most of these central symplasmic fields have a triangular geometry and are relatively small in size. Plants that are induced to flower by exposure to a single long day alter the geometry as well as the size of their central symplasmic field. After two subsequent days under short photoperiod the central symplasmic fields exhibit a circular form. Simultaneously. their size strongly increases both in an absolute sense and relative to the enlarging meristem. The geometric change in the fields is hypothesized to be due to recruitment of extra initial cells, required to support the increase in phyllotactic complexity. The proportional increase in field size is interpreted as an adjustment in the balance between the central and peripheral zone of the SAM, accompanying the shift from leaf production to flower formation. [less ▲]

Detailed reference viewed: 21 (1 ULg)
Full Text
Peer Reviewed
See detailControl of proliferation, endoreduplication and differentiation by the Arabidopsis E2Fa-DPa transcription factor
De Veylder, L.; Beeckman, T.; Beemster, G. T. S. et al

in EMBO Journal (2002), 21(6), 1360-1368

New plant cells arise at the meristems, where they divide a few times before they leave the cell-cycle program and start to differentiate. Here we show that the E2Fa-DPa transcription factor of ... [more ▼]

New plant cells arise at the meristems, where they divide a few times before they leave the cell-cycle program and start to differentiate. Here we show that the E2Fa-DPa transcription factor of Arabidopsis thaliana is a key regulator determining the proliferative status of plant cells. Ectopic expression of E2Fa induced sustained cell proliferation in normally differentiated cotyledon and hypocotyl cells. The phenotype was enhanced strongly by the co-expression of E2Fa with its dimerization partner, DPa. In endoreduplicating cells, E2Fa-DPa also caused extra DNA replication that was correlated with transcriptional induction of S phase genes. Because E2Fa-DPa transgenic plants arrested early in development, we argue that controlled exit of the cell cycle is a prerequisite for normal plant development. [less ▲]

Detailed reference viewed: 7 (1 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 23 (1 ULg)