Bibliografías temáticas / Plant secondary cell walls

Literatura académica sobre el tema "Plant secondary cell walls"

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Publicado: 20 de abril de 2024

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Artículos de revistas sobre el tema "Plant secondary cell walls"

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Avci, Utku. "Trafficking of Xylan to Plant Cell Walls". Biomass 2, n.º 3 (25 de agosto de 2022): 188–94. http://dx.doi.org/10.3390/biomass2030012.

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Plant cell walls are classified as primary and secondary walls. The primary wall is necessary for plant morphogenesis and supports cell growth and expansion. Once the growth and expansion ceases, specialized cells form secondary walls in order to give strength and rigidity to the plant. Secondary cell walls are the main constituent of woody biomass. This biomass is raw material for industrial products, food, and biomaterials. Recently, there are an increasing number of studies using biomass for biofuel production and this area has gained importance. However, there are still many unknowns regarding the synthesis and structure of complex polysaccharides forming biomass. Cellulose, being one of the main components of the cell wall, is synthesized at the plasma membrane by cellulose synthase complexes and does not require transportation. On the other hand, pectin and hemicelluloses are synthesized by enzymes located in the Golgi apparatus. Therefore, they need to be transported to the plasma membrane. Even though this transport mechanism is very important, it is one of the least understood parts of the endomembrane system. Xylan is the major hemicellulose in many biomasses and is important for renewable material production. There is limited knowledge about the cellular trafficking of xylan. In this review, we cover the current information and what we know about the vesicular transport of xylan to the cell wall.
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Wightman, Raymond y Simon Turner. "Digesting the indigestible: Biosynthesis of the plant secondary wall". Biochemist 33, n.º 2 (1 de abril de 2011): 24–28. http://dx.doi.org/10.1042/bio03302024.

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Biofuels have recently been the subject of intense debate with regard to‘food versus fuel’. Consequently, attention has focused upon so-called ‘second-generation’ biofuels that use alternatives to food-based feedstocks. In the best-developed forms of second-generation biofuels, sugars from starch digestion could be replaced with sugars released from the plant cell walls. This biomass could come from either agricultural residue, such as part of the maize culm, or from purpose grown biofuel crops, such as Miscanthus or Switchgrass (Panicum virgatum), that generate huge yields even when grown on marginal land with minimal agricultural inputs. For these and other potential bioenergy crops such as trees, the majority of the plant biomass is composed of woody secondary cell walls. If all cell wall sugars were readily accessible to fermenting micro-organisms, a 5 kg log could theoretically produce up to 2.5 litres of ethanol. The secondary cell walls are frequently the first line of defence against pests and pathogens, as well as providing structure and support for upward plant growth (Figure 1). Consequently, by their very nature, secondary cell walls are designed for strength and to resist degradation. The compact organization of the wall makes its digestion, a process known as saccharification, very difficult so biomass is currently too costly to be a viable feedstock. Knowledge of how the walls are constructed, however, would allow us to efficiently deconstruct them. This article gives an overview of secondary walls and potential modifications expected to be beneficial to improved biofuel production.
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Ma, Yingxuan, Luke Stafford, Julian Ratcliffe, Antony Bacic y Kim L. Johnson. "WAKL8 Regulates Arabidopsis Stem Secondary Wall Development". Plants 11, n.º 17 (2 de septiembre de 2022): 2297. http://dx.doi.org/10.3390/plants11172297.

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Wall-associated kinases/kinase-likes (WAKs/WAKLs) are plant cell surface sensors. A variety of studies have revealed the important functions of WAKs/WAKLs in regulating cell expansion and defense in cells with primary cell walls. Less is known about their roles during the development of the secondary cell walls (SCWs) that are present in xylem vessel (XV) and interfascicular fiber (IF) cells. In this study, we used RNA-seq data to screen Arabidopsis thaliana WAKs/WAKLs members that may be involved in SCW development and identified WAKL8 as a candidate. We obtained T-DNA insertion mutants wakl8-1 (inserted at the promoter region) and wakl8-2 (inserted at the first exon) and compared the phenotypes to wild-type (WT) plants. Decreased WAKL8 transcript levels in stems were found in the wakl8-2 mutant plants, and the phenotypes observed included reduced stem length and thinner walls in XV and IFs compared with those in the WT plants. Cell wall analysis showed no significant changes in the crystalline cellulose or lignin content in mutant stems compared with those in the WT. We found that WAKL8 had alternative spliced versions predicted to have only extracellular regions, which may interfere with the function of the full-length version of WAKL8. Our results suggest WAKL8 can regulate SCW thickening in Arabidopsis stems.
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4

Blanchette, Robert A., Kory R. Cease, André R. Abad, Todd A. Burnes y John R. Obst. "Ultrastructural characterization of wood from Tertiary fossil forests in the Canadian Arctic". Canadian Journal of Botany 69, n.º 3 (1 de marzo de 1991): 560–68. http://dx.doi.org/10.1139/b91-076.

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Micromorphological and ultrastructural characterization of fossil gymnosperm wood from Comwallis Island, Axel Heiberg Island, and Ellesmere Island in the Canadian High Arctic showed the changes that have occurred in cell walls of wood during 20–60 million years of burial. No evidence of permineralization was observed. Wood with rounded cells, thick secondary walls, and intercellular spaces was common in all samples. Secondary walls were eroded and swollen. A transition from an organized secondary wall, with altered but visible microfibrillar structure, to an electron-dense, amorphous material was evident in cell walls. The amorphous material appeared to form primarily in the secondary walls near cell lumina and along cracks that extended into the walls. The middle lamellae were often expanded in size and had convoluted shapes. Hemicellulose degradation appeared to precede cellulose degradation. Samples exhibiting cell walls with increased amorphous material had the greatest lignin and lowest cellulose concentrations. Hemicellulose concentration was extremely low in all Eocene and Paleocene samples. The lignin content of Miocene wood was 47.9%, whereas the Eocene and Paleocene samples ranged from 66 to 84%. Tracheids from extensively degraded samples were distorted and collapsed, and in some cases the cells appeared compressed together. Although the residual amorphous middle lamellae and secondary walls were fused together, the outlines of original cells were visible. Chemical analyses and ultrastructural data indicated that a nonbiological degradation was responsible for the deterioration of the arctic fossil wood samples. Key words: wood deterioration, lignin, hemicelluloses, cellulose, wood ultrastructure, coal formation, fossil wood.
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Pesquet, Edouard, Andrey V. Korolev, Grant Calder y Clive W. Lloyd. "Mechanisms for shaping, orienting, positioning and patterning plant secondary cell walls". Plant Signaling & Behavior 6, n.º 6 (junio de 2011): 843–49. http://dx.doi.org/10.4161/psb.6.6.15202.

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Terrett, Oliver M. y Paul Dupree. "Covalent interactions between lignin and hemicelluloses in plant secondary cell walls". Current Opinion in Biotechnology 56 (abril de 2019): 97–104. http://dx.doi.org/10.1016/j.copbio.2018.10.010.

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7

Busse-Wicher, Marta, Nicholas J. Grantham, Jan J. Lyczakowski, Nino Nikolovski y Paul Dupree. "Xylan decoration patterns and the plant secondary cell wall molecular architecture". Biochemical Society Transactions 44, n.º 1 (9 de febrero de 2016): 74–78. http://dx.doi.org/10.1042/bst20150183.

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The molecular architecture of plant secondary cell walls is still not resolved. There are several proposed structures for cellulose fibrils, the main component of plant cell walls and the conformation of other molecules is even less well known. Glucuronic acid (GlcA) substitution of xylan (GUX) enzymes, in CAZy family glycosyl transferase (GT)8, decorate the xylan backbone with various specific patterns of GlcA. It was recently discovered that dicot xylan has a domain with the side chain decorations distributed on every second unit of the backbone (xylose). If the xylan backbone folds in a similar way to glucan chains in cellulose (2-fold helix), this kind of arrangement may allow the undecorated side of the xylan chain to hydrogen bond with the hydrophilic surface of cellulose microfibrils. MD simulations suggest that such interactions are energetically stable. We discuss the possible role of this xylan decoration pattern in building of the plant cell wall.
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8

Seago, Jr., James L., Carol A. Peterson y Daryl E. Enstone. "Cortical ontogeny in roots of the aquatic plant, Hydrocharis morsus-ranae L." Canadian Journal of Botany 77, n.º 1 (1 de junio de 1999): 113–21. http://dx.doi.org/10.1139/b98-210.

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Tissues in adventitious roots of Hydrocharis morsus-ranae L. developed from a four-tiered apical meristem. A set of periclinal divisions in the outermost layer of the ground meristem produced a hypodermis, which was normally uniformly biseriate. Aerenchyma formed from the adjacent inner layer of the cortex by a series of cell divisions and cell lyses; three- to five-celled, radial aerenchyma strands formed by periclinal divisions in radial cell files 0.3-5 mm behind the apex. Intervening cells underwent anticlinal and periclinal divisions followed by cell lyses within 1 mm of the apex to produce air spaces. Aerenchyma formation in this species is unusual and presents a unique system suitable for a study of developmentally programmed cell death in parenchyma cells. The endodermis formed a complete Casparian band about 10 mm behind the root apex and did not develop further; it had neither suberin lamellae nor secondary walls. The hypodermis was parenchymatous and was without Casparian bands, suberin lamellae, and secondary walls. Following acid digestion, the wavy walls of the endodermis and the walls of the epidermis remained.Key words: aerenchyma, cell death, endodermis, Hydrocharis, hypodermis, root development.
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Idris, Nurul A., Maketelana Aleamotuʻa, David W. McCurdy y David A. Collings. "The Orchid Velamen: A Model System for Studying Patterned Secondary Cell Wall Development?" Plants 10, n.º 7 (2 de julio de 2021): 1358. http://dx.doi.org/10.3390/plants10071358.

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Understanding the mechanisms through which plants generate secondary cell walls is of more than academic interest: the physical properties of plant-derived materials, including timber and textiles, all depend upon secondary wall cellulose organization. Processes controlling cellulose in the secondary cell wall and their reliance on microtubules have been documented in recent decades, but this understanding is complicated, as secondary walls normally form in the plant’s interior where live cell imaging is more difficult. We investigated secondary wall formation in the orchid velamen, a multicellular epidermal layer found around orchid roots that consists of dead cells with lignified secondary cell walls. The patterns of cell wall ridges that form within the velamen vary between different orchid species, but immunolabelling demonstrated that wall deposition is controlled by microtubules. As these patterning events occur at the outer surface of the root, and as orchids are adaptable for tissue culture and genetic manipulation, we conclude that the orchid root velamen may indeed be a suitable model system for studying the organization of the plant cell wall. Notably, roots of the commonly grown orchid Laelia anceps appear ideally suited for developing this research.
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Keplinger, Tobias, Johannes Konnerth, Véronique Aguié-Béghin, Markus Rüggeberg, Notburga Gierlinger y Ingo Burgert. "A zoom into the nanoscale texture of secondary cell walls". Plant Methods 10, n.º 1 (2014): 1. http://dx.doi.org/10.1186/1746-4811-10-1.

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Tesis sobre el tema "Plant secondary cell walls"

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Escamez, Sacha. "Xylem cells cooperate in the control of lignification and cell death during plant vascular development". Doctoral thesis, Umeå universitet, Institutionen för fysiologisk botanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-115787.

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The evolutionary success of land plants was fostered by the acquisition of the xylem vascular tissue which conducts water and minerals upwards from the roots. The xylem tissue of flowering plants is composed of three main types of cells: the sap-conducting tracheary elements (TE), the fibres which provide mechanical support and the parenchyma cells which provide metabolic support to the tissue. Both the TEs and the fibres deposit thick polysaccharidic secondary cell walls (SCWs), reinforced by a rigid phenolic polymer called lignin. The cell walls of TEs form efficient water conducting hollow tubes after the TEs have undergone programmed cell death (PCD) and complete protoplast degradation as a part of their differentiation. The work presented in this thesis studied the regulation of TE PCD by characterizing the function of the candidate PCD regulator METACASPASE 9 (MC9) in Arabidopsis thaliana xylogenic cell suspensions. These cell suspensions can be externally induced to differentiate into a mix of TEs and parenchymatic non-TE cells, thus representing an ideal system to study the cellular processes of TE PCD. In this system, TEs with reduced expression of MC9 were shown to have increased levels of autophagy and to trigger the ectopic death of the non-TE cells. The viability of the non-TE cells could be restored by down-regulating autophagy specifically in the TEs with reduced MC9 expression. Therefore, this work showed that MC9 must tightly regulate the level of autophagy during TE PCD in order to prevent the TEs from becoming harmful to the non-TEs. Hence, this work demonstrated the existence of a cellular cooperation between the TEs and the surrounding parenchymatic cells during TE PCD. The potential cooperation between the TEs and the neighbouring parenchyma during the biosynthesis of lignin was also investigated. The cupin domain containing protein PIRIN2 was found to regulate TE lignification in a non-cell autonomous manner in Arabidopsis thaliana. More precisely, PIRIN2 was shown to function as an antagonist of positive transcriptional regulators of lignin biosynthetic genes in xylem parenchyma cells. Part of the transcriptional regulation by PIRIN2 involves chromatin modifications, which represent a new type of regulation of lignin biosynthesis. Because xylem constitutes the wood in tree species, this newly discovered regulation of non-cell autonomous lignification represents a potential target to modify lignin biosynthesis in order to overcome the recalcitrance of the woody biomass for the production of biofuels.
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2

Karlsson, Marlene. "Molecular factors involved in the formation of secondary vascular tissues and lignification in higher plants : studies of CuZn-SOD and members of MYB and zinc-finger transcription factor families /". Umeå : Dept. of Forest Genetics and Plant Physiology, Swedish Univ. of Agricultural Sciences, 2003. http://epsilon.slu.se/s280.pdf.

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Bonham, Victoria Anne. "Secondary cell wall specific proteins in plants". Thesis, Royal Holloway, University of London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312839.

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Islam, Azharul. "Cell-walls of growing plant cells". Thesis, University of Westminster, 2013. https://westminsterresearch.westminster.ac.uk/item/8z033/cell-walls-of-growing-plant-cells.

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The plant primary cell wall is a three-dimensional interwoven network of cellulose microfibrils, cross-linked by xyloglucan and dispersed in a pectin matrix. It has been suggested that in the wall of growing plant cells, xyloglucan is bound to the rigid cellulose microfibrils by hydrogen bonds and holds the microfibrils together by forming molecular tethers, which is referred to as the ‘sticky network’ model. Plant growth occurs when these tethers are peeled from the microfibrils by expansins or broken by glycosidases or transglycosylases. A number of researchers have presented theoretical difficulties and observations inconsistent with this model and a new hypothesis has been proposed, claiming that the cellulose – xyloglucan cross-links may act as ‘scaffolds’ holding the microfibrils apart. Analogies with synthetic polymers suggests that the spacing between the cellulose microfibrils may be an important determinant of the mechanical properties of the cell wall and the results presented in this thesis support this hypothesis. Water contents of Acetobacter xylinus synthesized cellulose based cell wall analogues (as a mimic of primary cell wall) and sunflower hypocotyl cell walls were altered using high molecular weight polyethylene glycol (PEG) solution, and their extension under a constant load was measured using a creep extensiometer and showed that there were clear reduction (30-35%) in extensibility suggesting that water content of the wall and therefore the cell wall free volume directly influence wall extensibility. When hydration of A. xylinus cellulose composite pellicles was reduced using PEG 6000 solution and re-hydrated in buffer solution, followed by treatment with α-expansin or snail acetone powder extract, it was found that expansin and snail powder extracts caused a rapid rehydration of the composites and that the pellicles only returned to their original weights after these treatments, suggesting that expansin and snail powder can increase the free volume of the wall perhaps contributing to the increases in extensibility that they cause. Assays on cell wall fragments also indicated that expansin increased the cell wall free volume, demonstrated by changes of the turbidity of fragment suspensions. The role of pectic polysaccharide, RG-II, in cell wall biomechanics was also investigated using mechanical and biochemical testing of available Arabidopsis thaliana cell wall mutants and by incorporating RG-II (purified from red wine) with Acetobacter cellulose. It was demonstrated that RG-II significantly increased the hydration of cellulose composite; hydration rate was 15 -16% more than the composite without RG-II and thus increased the pellicle extensibility. From the results, it is evidenced that cell wall extension is not only the consequences of breaking hydrogen bonds between cellulose microfibrils and xyloglucan by expansins or glycosidases and transglycosylases, but also a wider range of factors are involved including cell wall water content, cell wall free volume and the pectic polymers, especially RG-II.
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5

Cuello, Clément. "Vers l'élaboration d'un modèle de construction des parois secondaires des fibres de bois chez le peuplier". Electronic Thesis or Diss., Orléans, 2021. https://theses.univ-orleans.fr/prive/accesESR/2021ORLE3118_va.pdf.

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Les arbres atteignent des hauteurs et des durées de vie considérables grâce aux propriétés remarquables de leur bois. En effet, le bois remplit trois fonctions principales : (i) la conduction de la sève brute de la racine au houppier, (ii) le soutien mécanique de la masse toujours en augmentation de l'arbre en croissance et (iii) le stockage de réserves temporaires, capitales pour la pérennité de l'arbre. Chez les angiospermes, les vaisseaux, les fibres et les rayons parenchymateux sont, respectivement, affiliés à ces fonctions. Chacune de ces cellules possède son propre schéma de développement. Par ailleurs, la composition et la structure des parois de ces cellules varient considérablement en fonction des stades de développement et des conditions environnementales. Cette complexité représente donc un frein à l’étude des mécanismes moléculaires de la formation du bois. Cette difficulté peut être contournée par le développement d’approches à l’échelle cellulaire.La thèse présentée ici vise à une caractérisation du développement des fibres, plus particulièrement de leurs parois secondaires, par le déploiement d’outils de caractérisation à l’échelle cellulaire et d’une analyse intégrative à cette échelle. Le développement d’une méthode de caractérisation des parois à l’échelle cellulaire, l’imagerie hyperspectrale en ATR-FTIR, a permis une analyse fine des différences entre types cellulaires au sein d’un arbre et entre types de bois pour un même type cellulaire. L’étude de données transcriptomiques obtenues par RNA-Seq de fibres et rayons micro disséqués a, elle, permis d’identifier des différences transcriptionnelles entre ces deux types cellulaires. La combinaison de ces deux résultats a permis d’identifier des acteurs semblant majeurs dans le développement des fibres de bois. Ce travail de thèse ouvre donc des perspectives de recherche permettant de mieux comprendre les mécanismes moléculaires associés à la formation des fibres de bois
Trees are able to grow high et survive many years thanks to their wood properties. Wood delivers three major functions in trees : (i) water conduction, (ii) mechanical support et (iii) nutrient storage. In Angiosperm trees, vessels, fibers et parenchyma rays are respectively assigned to these functions, each of them following their own development scheme. Cell wall composition et structure varies greatly depending on cell type, developmental stage et environmental conditions. This complexity therefore represents a hindrance to study the molecular mechanisms of wood formation. However, this can be circumvented by the development of cell-specific approaches.This work aims at characterizing fiber development, focusing on their secondary cell wall, developing cell-specific methods et integrative analysis at the cell level. Development of ATR-FTIR hyperspectral imaging enabled to finely characterize differences in cell wall composition between cell types in a tree et within cell types in different types of wood. Transcriptomics data obtained by RNA-Seq of microdissected fibers et rays gave rise to major differences in the transcriptome of these two cell types. Combining both kind of result led to the identification of key players in fibers development. Hence, this work opens up new research hypothesis, which could lead to a better understanding of the molecular mechanisms underlying wood fiber development, including from a dynamic perspective
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Murugesan, Yogesh Kumar. "Anisotropic soft matter models for plant cell walls". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=117093.

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This thesis uses theory and simulation to elucidate the principles and mechanisms that govern the thermodynamics, material science, and rheology of biological anisotropic soft matter that are involved in growth/self-assembly/material processing in plant cell walls, a multi-functional biological fibrous composite. The plant cell wall can be considered as a reinforced biological membrane consisting of cellulose microfibrils (CMFs) of high tensile strength embedded in a polysaccharide matrix. These CMFs in the extracellular matrix are oriented instrategic directions and generate commonly observed textures such as line, ring, helix, crossed helix and helicoids. The orientation of CMFs governs the physical properties of wood, controls the shape of the cell and contributes to themorphology at the tissue and organ level. Two models are used in this thesis, depending on the concentration of CMFs.At concentration of CMFs below Onsager critical limit, we develop an integrated mechanical model that describes nematic liquid crystalline self-assembly of rigid fibers on an arbitrarily curved 2D fluid membrane to demonstrate the possibility of the CMF orientation imparted by the interaction between membrane curvature and embedded fiber order. This curvature driven planar self assembly model can predict and explain the observed line, ring and helical cell wall textures. These predictions are partially validated through available experimental observations. An integrated shape and nematic order equation developed in this thesis gives a complete model whose solution describes the coupled membraneshape and fiber order state. The validated model is then used to analyze the structure and mechanics of biological and biomimetic fiber-laden membranes of variable curvature. The statics of anisotropic fiber-laden membranes developed inthis model is integrated with the planar nematodynamics of fibers and the dynamics of isotropic membranes to formulate a viscoelastic model to study dynamic remodeling of plant cell wall during growth and morphogenesis. The novel coupling between in-plane fiber orientation and order and membrane curvature formulated this thesis has the potential to open up a novel venue to control two dimensional anisotropic soft matter with tailored functionalities. When the concentration of the CMFs exceeds Onsager's critical fiber concentration threshold, the interaction between these CMFs results in theiralignment in a specific direction as an attempt to minimize the excluded volume of the CMFs. A mathematical model based on the Landau–de Gennes theory of liquid crystals is used to simulate defect textures arising in the domain of chiralself-assembly due to the presence of secondary phases such as pit canal and cell lumens. In addition to providing information on material properties and length scales that cannot be experimentally measured in vivo, the simulated transient defect pattern confirms for first time the long postulated formation mechanism of helicoidal plywoods through liquid crystalline self-assembly. The model is further extended to investigate defect textures and liquid crystalline (LC) phases observed in polygonal arrangement of cylindrical particles embedded in a cholesteric liquid crystal matrix. These validated findings provide a comprehensive set of trends and mechanisms that contribute to the evolving understanding of biological plywoods and serve as a platform for future biomimetic applications.The integration of soft matter physics theories and models with actual biological data for plant cell walls provides a foundation for understanding growth, form, and function and a platform for biomimetic innovation.
Cette thèse utilise la théorie et la simulation pour élucider les principes et mécanismes qui gouverne la hermodynamique, la science des matériaux, et la rhéologie de la matière biologique molle anisotropique qui est impliquée dans ledéveloppement/auto-assemblage/la transformation des parois cellulaires de plantes, un composite biologique fibreux multifonctionnel. Les parois cellulaires de plantes peuvent être considérées comme des membranes biologiques renforcées consistant en des microfibres de cellulose (CMFs) de hautes ténacités contenues dans une matrice de polysaccaride. Ces CMFs dans la matrice extracellulaire sont orientés dans une direction stratégique hélices et des hélicoïdes. L'orientation des CMFs gouverne les propriétés physiques du bois et contrôle la forme des cellules. Deux modèles sont employés dans cette thèse dépendamment de la concentration en CMFs. A la concentration de CMFs dessous la limite critique de Onsager, nous développons un modèle mécanique intégré qui décrit un auto-assemblage de fibres rigides de type cristal liquide nématique sur une membrane courbée bidimensionnelle arbitraire afin de démontrer la possibilité de l'orientation des CMFs indue par les interactions entre la courbature de la membrane et l'organisation fibrillaire intrinsèque. Cette auto-assemblage planaire indus par la courbature peut prédire et expliquer les lignes, annaux et textures hélicoïdales observées dans les parois cellulaires. Ces prédictions sont partiellement validées au travers d'observations expérimentales publiés. Une équation décrivant l'ordre nématique et la forme intégrée qui a été développé dans cette thèse fournis un modèle complet dont la solution décrit le couplage entre l'alignement des fibres et la forme de la membrane. Le model validé est par la suite utilisé à fin d'analyser la structure et la mécanique de membrane fibreuses biologiques et biomimétiques de courbatures variables. La statique des membranes fibreuses anisotropes développés dans ce modèle est intégrée avec la némato-dynamique planaire des fibres et la dynamique des membranes isotropes afin de formuler un modèle viscoélastique pour étudier le remodelage dynamique des CMF durant leur développement et morphogénèse. Le nouveau couplage entre l'orientation fibrillaire planaire et l'ordre ainsi que la courbature de la membrane formulé dans cette thèse à le potentiel d'ouvrir de nouvelles avenues pour contrôler l'ordre bidimensionnel de matière molle selon des propriétés bien définies. Quand la concentration en CMFs excède la limite critique en fibre de Onsager, l'interaction entre les CMFs résulte en un alignement dans une direction spécifique qui tente de minimiser le volume exclu de CMFs. Un modèle mathématique basé sur la théorie de Landau de Gennes des cristaux liquides est utilisé pour simuler les textures de défauts survenant dans un chirale d'auto assemblage du à la présence de phases secondaires tel que les lumens cellulaires. En plus de fournir de l'information sur les propriétés matériels et les ordres de grandeurs qui ne peuvent être mesuré expérimentalement in vivo, les motifs des défauts transitoires simulés confirment pour la première fois le mécanisme de formation des assemblages hélicoïdaux. Le modèle est de plus étendu pour investiguer les textures de défauts et les phases liquides cristallines (LC) observées dans les arrangements polygonaux de particules cylindriques inclus dans des matrices de cristaux liquide cholestériques. Ces découvertes validées fournissent un ensemble de mécanismes qui contribues à faire évoluer la compréhension des assemblages lamellaires biologiques et servent de plateforme pour de futur développement d'applications biomimétiques. L'intégration des théories et des modèles de la matière molle avec des données biologique concrète pour les parois cellulaires fournissent des fondement pour la compréhension du développement, de formation et fonctionnalité ainsi qu'une plateforme pour l'innovation biomimétique
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Sene, Christophe F. B. "Infrared microspectroscopy and raman spectroscopy of plant cell walls". Thesis, University of East Anglia, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240996.

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Nunan, Kylie. "Cell wall metabolism in developing grape berries /". Title page, contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09APSP/09pspn972.pdf.

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John, Melford Apti. "Post-harvest changes in cell walls of mango fruits". Thesis, Royal Holloway, University of London, 1985. http://repository.royalholloway.ac.uk/items/e6f2ec32-7c86-4106-a945-0ac589c09f14/1/.

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Comparative work on the structure of the cell walls of red kidney bean hypocotyls and mesocarp from unripe and ripe mango fruits showed significant differences. Cell-wall fractions from each were obtained using solvent extraction (water, alkali and acid) and enzymic (endopolygalacturonase) degradation procedures. The monosaccharide composition of each fraction was determined after TFA-hydrolysis by TLC-analysis. Greatest variation in monosaccharide compositions was observed in the water-soluble fractions which accounted for 18%, 48% and 11% of the cell walls of the bean, unripe and ripe mango, respectively. Water-soluble carbohydrates present in the mango pulp were examined by TLC, gel-filtration and ion-exchange methods. Only sucrose, fructose, glucose and high-MW polysaccharides were detected. The ripe mango contained 8 times more soluble polysaccharide than the unripe. In the ripe fruit the approximate MW of the polysaccharide fraction, which was rich in uronic acid was 40,000. In the unripe fruitpolysaccharides with MW's ranging from 40,000 to > 300,000 were detected. These polymers contained much smaller proportions of uronic acid than those from the ripe mesocarp. A crude 3 M LiCl enzyme extract from the cell walls of the ripe mango was able to solubilize 14% of prepared cell walls from the unripe fruit. The mechanism of this process was investigated. Endo-enzymes involved could not be identified. The involvement of b-galactosidase in cell-wall degradation was examined. Using p-nitrophenyl-b-D-galactopyranoside as substrate, 3 wall-bound forms of the enzyme were found in the ripe fruit and 2 in the unripe. Four soluble forms which were different from the wall-bound forms were observed in the ripe fruit. Three of these were present in the unripe fruit. The action of the enzyme forms on mango pectin and cell walls was examined. There was no evidence that any were directly implicated in cell-wall degradation. Wall-bound exopolygalacturonase was detected for the first time in the mango fruit.
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McCann, Maureen C. "Architecture of the plant extracellular matrix". Thesis, University of East Anglia, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279709.

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Libros sobre el tema "Plant secondary cell walls"

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Carpita, N. C., M. Campbell y M. Tierney, eds. Plant Cell Walls. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0668-2.

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Geitmann, Anja. Plant Cell Walls. Boca Raton: CRC Press, 2023. http://dx.doi.org/10.1201/9781003178309.

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T, Brett C. y Hillman John R, eds. Biochemistry of plant cell walls. Cambridge [Cambridgeshire]: Cambridge University Press, 1985.

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1921-, Linskens H. F., Jackson J. F. 1935- y Bacic A, eds. Plant cell wall analysis. Berlin: Springer, 1996.

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F, Linskens H., Jackson J. F y Bacic A, eds. Plant cell wall analysis. Berlin: Springer, 1996.

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Brett, C. y K. Waldron. Physiology and Biochemistry of Plant Cell Walls. Dordrecht: Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-010-9641-6.

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K, Waldron, ed. Physiology and biochemistry of plant cell walls. London: Unwin Hyman, 1990.

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Fukuda, H. Plant cell wall patterning and cell shape. Hoboken, New Jersey: John Wiley & Sons Inc., 2015.

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Phillip, Morris y International Association of Plant Cell and Tissue Culture., eds. Secondary metabolism in plant cell cultures. Cambridge: Cambridge University Press, 1986.

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Cell Wall Meeting (4th 1986 Paris, France). Cell walls '86: Proceedings of the Fourth Cell Wall Meeting, Paris, September 10th-12th, 1986. Editado por Vian Brigitte, Goldberg R y Reis Daniéle. Paris: Université Pierre et Marie Curie, École Normal Supérieure, 1986.

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Capítulos de libros sobre el tema "Plant secondary cell walls"

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Turner, Simon R., Neil Taylor y Louise Jones. "Mutations of the secondary cell wall". En Plant Cell Walls, 209–19. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0668-2_13.

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Koch, Gerald y Uwe Schmitt. "Topochemical and Electron Microscopic Analyses on the Lignification of Individual Cell Wall Layers During Wood Formation and Secondary Changes". En Plant Cell Monographs, 41–69. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-36491-4_2.

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Shafi, Amrina y Insha Zahoor. "Plant Survival and Tolerance Under High Salinity: Primary and Secondary Cell Wall-Sensing Mechanism". En Salt Stress, Microbes, and Plant Interactions: Causes and Solution, 129–46. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-13-8801-9_6.

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Sandstrom, Richard P. y W. David Loomis. "Cell Walls and Secondary Products as Obstacles to Plant Enzyme Isolation: Problems and Solutions, Including a Simple Liquid-Nitrogen Homogenizer for Bulk Tissue Extraction". En The Metabolism, Structure, and Function of Plant Lipids, 45–52. Boston, MA: Springer New York, 1987. http://dx.doi.org/10.1007/978-1-4684-5263-1_6.

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Civardi, Laura, Alain Murigneux, Patricia Tatout, Pere Puigdomènech y Joan Rigau. "Molecular Cloning and Characterization of two cDNAs Encoding Enzymes Required for Secondary Cell Wall Biosynthesis in Maize". En Cellular Integration of Signalling Pathways in Plant Development, 135–46. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-642-72117-5_13.

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Crang, Richard, Sheila Lyons-Sobaski y Robert Wise. "Cell Walls". En Plant Anatomy, 155–79. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-77315-5_5.

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Noguchi, Tetsuko. "Cell Walls". En Atlas of Plant Cell Structure, 137–56. Tokyo: Springer Japan, 2014. http://dx.doi.org/10.1007/978-4-431-54941-3_7.

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Bidlack, James E. y William V. Dashek. "Plant cell walls". En Plant Cells and their Organelles, 209–38. Chichester, UK: John Wiley & Sons, Ltd, 2016. http://dx.doi.org/10.1002/9781118924846.ch9.

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Moore, John P., Maïté Vicré, Eric Nguema-Ona, Azeddine Driouich y Jill M. Farrant. "Drying Out Walls". En Plant Cell Walls, 441–51. Boca Raton: CRC Press, 2023. http://dx.doi.org/10.1201/9781003178309-22.

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Vissenberg, Kris y Herman Höfte. "Cell Wall-Related Mechanisms Underlying Plant Cell Expansion". En Plant Cell Walls, 127–46. Boca Raton: CRC Press, 2023. http://dx.doi.org/10.1201/9781003178309-6.

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Actas de conferencias sobre el tema "Plant secondary cell walls"

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Tran, Thi Ngoc Anh. "Ectopic secondary cell wall formation in Arabidopsis by overexpression of an unusual MYB transcription factor from poplar". En ASPB PLANT BIOLOGY 2020. USA: ASPB, 2020. http://dx.doi.org/10.46678/pb.20.1052914.

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Faisal, Tanvir R., Nicolay Hristozov, Tamara Western, Alejandro Rey y Damiano Pasini. "A Multiscale Model to Determine the Stiffness of Collenchyma Tissue in Rheum Rhabarbarum". En ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-39676.

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The stiffness of plant tissue largely influences the overall mechanical response of plant organs, such as stems, branches and leaf petioles. This work examines the structural hierarchy of the plant tissue; in particular of the collenchyma tissue of the Rheum rhabarbarum. The goal of the paper is to develop a multiscale model capturing features of two orders of its structural hierarchy: cell wall and tissue architecture. The former is considered as a fiber reinforced composite, where the cellulose microfibril (CMF) is the main load bearing component. The longitudinal stiffness of the middle (S2) layer of the secondary cell wall is affected by the microfibril angle (MFA) up to 45° to a greater extent, which in turn plays a role in the overall wall stiffness. The latter, i.e. tissue architecture, influences the tissue stiffness through its random distribution of cells. Finite-edge Centroidal Voronoi Tessellation (FECVT) is used to model the non-periodic microstructure of the rhubarb collenchyma, whose effective elastic properties are obtained through finite element analysis. The results from the FECVT model show that the effective stiffness in the longitudinal direction is 15 to 25% higher than that in the transverse direction for relative density between 5 and 30%. The variation reflects the stiffening effect of the shape and size of the cells in the collenchyma tissue, as well as its aperiodic cellular distribution.
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Pilot, Guy, Sylvain Fauvel, Xavier Gosse y Guillaume de Dinechin. "Dismantling of Evaporators by Laser Cutting: Measurement of Secondary Emissions". En 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/icone14-89709.

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In order to dismantle the evaporators of an obsolete reprocessing plant in Marcoule, studies were carried out by IRSN (Institut de Radioprotection et de Suˆrete´ Nucle´aire)/DSU/SERAC in cooperation with CEA (power laser group) on the laser cutting of steel structures, on the request of COGEMA (now AREVA NC)/Marcoule (UP1 dismantling project manager) and CEA/UMODD (UP1 dismantling owner). The aim of these studies was: • to quantify and to characterize the secondary emissions produced by Nd-YAG laser cutting of Uranus 65 steel pieces representative of UP1 evaporator elements and to examine the influence of different parameters, • to qualify a prefiltration technique and particularly an electrostatic precipitator, • to compare the Nd-YAG used with other cutting tools previously studied. The experiments, which took place in a 35 m3 ventilated cutting cell, allow to underline the following points: • for the Uranus 65 steel, the sedimented dross, the deposits on the walls of the cutting cell and the aerosols drawn in the ventilation exhaust duct (∼ 275 m3/h), represent respectively between 92% and 99%, between 0.01% and 0.25% and between 1% and 8% of the total collected mass, • the attached slag varies much from one configuration to the other and can sometimes amount to a relatively important fraction of the total mass, • the kerves vary from 2 mm up to 7 mm for the Uranus 65 steel plates (thickness: 13.8 mm for the single plate and 12.8 + 3.5 mm for the double plate), • the exhausted aerosol mass per cut length (g/m) decreases with the cutting speed, varies neither with the stand-off nor with the gas pressure, is dependent upon the gas nature (for the double plate), increases with the laser power, is strongly affected by the nature of the steel (stainless steel or mild steel) and is independent upon the plate position, • the size distribution of aerosols is multimodal with a main mode often around 0.45 μm, • the electrostatic precipitator has been a satisfactory prefilter in the experiments with a filtration efficiency greater than 85% and the acoustic declogging system was very useful, • compared to other cutting tools already tested in similar conditions (reciprocating saw, 50 A plasma torch, 200 A plasma torch, grinder, 1 kW laser without assistant gas, arc-air and arc saw), the 4 kW laser produced less secondary emissions than all other tools and less aerosols than the other thermal tools.
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Baumann, Sven, Lucien Teunckens, Robert Walthéry, Patrick Lewandowski y Danny Millen. "The Results of Specific Efforts to Improve Techniques for the Decontamination of Concrete Surfaces in Nuclear Facilities". En ASME 2001 8th International Conference on Radioactive Waste Management and Environmental Remediation. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/icem2001-1309.

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Abstract Belgoprocess started the industrial decommissioning of the main process building of the former EURO-CHEMIC reprocessing plant in 1990, after completion of a pilot project in which two buildings were emptied and decontaminated to background levels. The remaining structures were demolished and the concrete debris was disposed of as industrial waste and green field conditions restored. Decommissioning involves the removal and decontamination of equipment from each cell, the decontamination of the cell walls, ceilings and floors, and the dismantling of the ventilation system. These activities are followed by a complete monitoring in order to obtain the unconditional release of the remaining structures. In the earlier days, concrete walls with limited in depth contamination, were decontaminated using commercially available pneumatic hand scabblers. In addition, 3-headed, 5-headed and 7-headed hand-operated floor scabblers have been used. The pneumatic powered machines have adapted dust extraction systems around the scabbier heads. To improve the working conditions for the operators, and to increase capacity, scabblers have been progressively automised. Operation efficiency was significantly improved when shaving machines were introduced, using a diamond tipped rotary head, designed to give a smooth surface finish, which is easier to measure. The use of these machines resulted in a higher efficiency and a 30% reduction of secondary waste production. It also reduced the physical load to the operators due to the absence of machine vibration. The paper gives an overview of the specific efforts that have been put in improving the techniques for the decontamination of concrete surfaces at the decommissioning of the Eurochemic reprocessing plant in Dessel, Belgium.
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Mokshina, N. E., O. V. Gorshkov y T. A. Gorshkova. "Thickening of Plant Cell Walls: Scenarios and Directing". En IX Congress of society physiologists of plants of Russia "Plant physiology is the basis for creating plants of the future". Kazan University Press, 2019. http://dx.doi.org/10.26907/978-5-00130-204-9-2019-21.

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Quang, R. Do, V. Petitjean, F. Hollebecque, O. Pinet, T. Flament y A. Prod’homme. "Vitrification of HLW Produced by Uranium/Molybdenum Fuel Reprocessing in COGEMA’s Cold Crucible Melter". En ASME 2003 9th International Conference on Radioactive Waste Management and Environmental Remediation. ASMEDC, 2003. http://dx.doi.org/10.1115/icem2003-4594.

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The performance of the vitrification process currently used in the La Hague commercial reprocessing plants has been continuously improved during more than ten years of operation. In parallel COGEMA (industrial Operator), the French Atomic Energy Commission (CEA) and SGN (respectively COGEMA’s R&D provider and Engineering) have developed the cold crucible melter vitrification technology to obtain greater operating flexibility, increased plant availability and further reduction of secondary waste generated during operations. The cold crucible is a compact water-cooled melter in which the radioactive waste and the glass additives are melted by direct high frequency induction. The cooling of the melter produces a soldified glass layer that protects the melter’s inner wall from corrosion. Because the heat is transferred directly to the melt, high operating temperatures can be achieved with no impact on the melter itself. COGEMA plans to implement the cold crucible technology to vitrify high level liquid waste from reprocessed spent U-Mo-Sn-Al fuel (used in gas cooled reactor). The cold crucible was selected for the vitrification of this particularly hard-to-process waste stream because it could not be reasonably processed in the standard hot induction melters currently used at the La Hague vitrification facilities: the waste has a high molybdenum content which makes it very corrosive and also requires a special high temperature glass formulation to obtain sufficiently high waste loading factors (12% in molybednum). A special glass formulation has been developed by the CEA and has been qualified through lab and pilot testing to meet standard waste acceptance criteria for final disposal of the U-Mo waste. The process and the associated technologies have been also being qualified on a full-scale prototype at the CEA pilot facility in Marcoule. Engineering study has been integrated in parallel in order to take into account that the Cold Crucible should be installed remotely in one of the R7 vitrification cell. This paper will present the results obtained in the framework of these qualification programs.
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Zhu, Ying, Filomena Pettolino, Shaio-lim Mau y Tony Bacic. "CHARACTERIZATION OF ROOT CELL WALLS OF THE MEDICINAL PLANT PANAX NOTOGINSENG". En XXIst International Carbohydrate Symposium 2002. TheScientificWorld Ltd, 2002. http://dx.doi.org/10.1100/tsw.2002.683.

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Siemiawski, Oskar. "Tender Resonant X-ray Scattering at calcium K-edge to resolve cellulose microstructure in Arabidopsis primary plant cell walls". En ASPB PLANT BIOLOGY 2020. USA: ASPB, 2020. http://dx.doi.org/10.46678/pb.20.989679.

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Orfila, Caroline, Florence Dal Degan, Peter Ulvskov y Henrik V. Scheller. "BIOSYNTHESIS AND DEGRADATION OF O-ACETYLATED PECTIC POLYSACCHARIDES IN PLANT PRIMARY CELL WALLS". En XXIst International Carbohydrate Symposium 2002. TheScientificWorld Ltd, 2002. http://dx.doi.org/10.1100/tsw.2002.404.

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Gordeeva, E. P., A. R. Nazipova, P. V. Mikshina y T. A. Gorshkova. "Ramnogalacturonan I in the tertiary cell walls of fibers of various plants". En IX Congress of society physiologists of plants of Russia "Plant physiology is the basis for creating plants of the future". Kazan University Press, 2019. http://dx.doi.org/10.26907/978-5-00130-204-9-2019-130.

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Informes sobre el tema "Plant secondary cell walls"

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Delmer, Deborah P., Douglas Johnson y Alex Levine. The Role of Small Signal Transducing Gtpases in the Regulation of Cell Wall Deposition Patterns in Plants. United States Department of Agriculture, agosto de 1995. http://dx.doi.org/10.32747/1995.7570571.bard.

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The combined research of the groups of Delmer, Levine and Johnson has led to a number of interesting findings with respect to the function of the small GTPase Rac in plants and also opened up new leads for future research. The results have shown: 1) The Rac13 protein undergoes geranylgeranlyation and is also translocated to the plasma membrane as found for Rac in mammals; 2) When cotton Rac13 is highly- expressed in yeast, it leads to an aberrant phenotype reminiscent of mutants impaired in actin function, supporting a role for Rac13 in cytoskeletal organization; 3) From our searches, there is no strong evidence that plants contain homologs of the related CDC42 genes found in yeast and mammals; 4) We have identified a rather unique Rac gene in Arabidopsis that has unusual extensions at both the N- and C-terminal portions of the protein; 5) New evidence was obtained that an oxidative burst characterized by substantial and sustained production of H202 occurs coincident with the onset of secondary wall synthesis in cotton fibers. Further work indicates that the H202 produced may be a signal for the onset of this phase of development and also strongly suggests that Rac plays an important role in signaling for event. Since the secondary walls of plants that contain high levels of lignin and cellulose are the major source of biomass on earth, understanding what signals control this process may well in the future have important implications for manipulating the timing and extent of secondary wall deposition. 6) When the cotton Rac13 promoter is fused to the reporter gene GUS, expression patterns in Arabidopsis indicate very strong and specific expression in developing trichomes and in developing xyelm. Since both of these cell types are engaged in secondary wall synthesis, this further supports a role for Rac in signaling for onset of this process. Since cotton fibers are anatomically defined as trichomes, these data may also be quite useful for future studies in which the trichomes of Arabidopsis may serve as a model for cotton fiber development; the Rac promoter can therefore be useful to drive expression of other genes proposed to affect fiber development and study the effects on the process; 7) The Rac promoter has also been shown to be the best so far tested for use in development of a system for transient transformation of developing cotton fibers, a technique that should have many applications in the field of cotton biotechnology; 8) One candidate protein that may interact with Rac13 to be characterized further in the future is a protein kinase that may be analogous to the PAK kinase that is known to interact with Rac in mammals.
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Sharon, Amir y Maor Bar-Peled. Identification of new glycan metabolic pathways in the fungal pathogen Botrytis cinerea and their role in fungus-plant interactions. United States Department of Agriculture, 2012. http://dx.doi.org/10.32747/2012.7597916.bard.

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The involvement of glycans in microbial adherence, recognition and signaling is often a critical determinant of pathogenesis. Although the major glycan components of fungal cell walls have been identified there is limited information available on its ‘minor sugar components’ and how these change during different stages of fungal development. Our aim was to define the role of Rhacontaining-glycans in the gray mold disease caused by the necrotrophic fungus B. cinerea. The research was built on the discovery of two genes, Bcdhand bcer, that are involved in formation of UDP-KDG and UDP-Rha, two UDP- sugars that may serve as donors for the synthesis of cell surface glycans. Objectives of the proposed research included: 1) To determine the function of B. cinereaBcDh and BcEr in glycan biosynthesis and in pathogenesis, 2) To determine the expression pattern of BcDH and BcERand cellular localization of their encoded proteins, 3) Characterize the structure and distribution of Rha- containing glycans, 4) Characterization of the UDP-sugar enzymes and potential of GTs involved in glycanrhamnosylation. To address these objectives we generated a series of B. cinereamutants with modifications in the bchdhand bcergenes and the phenotype and sugar metabolism in the resulting strains were characterized. Analysis of sugar metabolites showed that changes in the genes caused changes in primary and secondary sugars, including abolishment of rhamnose, however abolishment of rhamnose synthesis did not cause changes in the fungal phenotype. In contrast, we found that deletion of the second gene, bcer, leads to accumulation of the intermediate sugar – UDP- KDG, and that such mutants suffer from a range of defects including reduced virulence. Further analyses confirmed that UDP-KDG is toxic to the fungus. Studies on mode of action suggested that UDP-KDG might affect integrity of the fungal cell wall, possibly by inhibiting UDP-sugars metabolic enzymes. Our results confirm that bcdhand bcerrepresent a single pathway of rhamnose synthesis in B. cinerea, that rhamnose does not affect in vitro development or virulence of the fungus. We also concluded that UDP-KDG is toxic to B. cinereaand hence UDP-KDG or compounds that inhibit Er enzymes and lead to accumulation of UDP-KDG might have antifungal activity. This toxicity is likely the case with other fungi, this became apparent in a collaborative work with Prof. Bart Thomma of Wageningen University, NETHERLANDS . We have shown the deletion of ER mutant in Verticillium dahlia gave plants resistance to the fungal infection.
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Dickman, Martin B. y Oded Yarden. Characterization of the chorismate mutase effector (SsCm1) from Sclerotinia sclerotiorum. United States Department of Agriculture, enero de 2015. http://dx.doi.org/10.32747/2015.7600027.bard.

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Sclerotinia sclerotiorum is a filamentous fungus (mold) that causes plant disease. It has an extremely wide range of hosts (>400 species) and causes considerable damage (annual multimillion dollar losses) in economically important crops. It has proven difficult to control (culturally or chemically) and host resistance to this fungus has generally been inadequate. It is believed that this fungus occurs in almost every country. Virulence of this aggressive pathogen is bolstered by a wide array of plant cell wall degrading enzymes and various compounds (secondary metabolites) produced by the fungus. It is well established that plant pathogenic fungi secrete proteins and small molecules that interact with host cells and play a critical role in disease development. Such secreted proteins have been collectively designated as “effectors”. Plant resistance against some pathogens can be mediated by recognition of such effectors. Alternatively, effectors can interfere with plant defense. Some such effectors are recognized by the host plant and can culminate in a programmed cell death (PCD) resistant response. During the course of this study, we analyzed an effector in Sclerotiniasclerotiorum. This specific effector, SsCM1 is the protein chorismatemutase, which is an enzyme involved in a pathway which is important in the production of important amino acids, such a Tryptophan. We have characterized the Sclerotiniaeffector, SsCM1, and have shown that inactivation of Sscm1 does not affect fungal vegetative growth, development or production of oxalic acid (one of this fungus’ secondary metabolites associated with disease) production. However, yhis does result in reduced fungal virulence. We show that, unexpectedly, the SsCM1 protein translocates to the host chloroplast, and demonstrated that this process is required for full fungal virulence. We have also determined that the fungal SsCM1 protein can interact with similar proteins produced by the host. In addition, we have shown that the fungal SsCM1 is able to suppress at least some of the effects imposed by reactive oxygen species which are produced as a defense mechanism by the host. Last, but not least, the results of our studies have provided evidence contradicting the current dogma on at least some of the mechanist aspects of how this pathogen infects the host. Contrary to previousons, indicating that this pathogen kills its host by use of metabolites and enzymes that degrade the host tissue (a process called necrotrophy), we now know that at least in the early phases of infection, the fungus interacts with live host tissue (a phenomenon known as biotrophy). Taken together, the results of our studies provide novel insights concerning the mechanistic aspects of Sclerotinia-host interactions. We hope this information will be used to interfere with the disease cycle in a manner that will protect plants from this devastating fungus.
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Darvill, Alan, Michael G. Hahn, Malcolm A. O'Neill y William S. York. Structural Studies of Complex Carbohydrates of Plant Cell Walls. Office of Scientific and Technical Information (OSTI), febrero de 2015. http://dx.doi.org/10.2172/1170244.

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Darvill, A. Structural studies of complex carbohydrates of plant cell walls. Office of Scientific and Technical Information (OSTI), agosto de 1990. http://dx.doi.org/10.2172/6158915.

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Alan G. Darvill. Structural studies of complex carbohydrates of plant cell walls. Office of Scientific and Technical Information (OSTI), diciembre de 1995. http://dx.doi.org/10.2172/764078.

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Manulis-Sasson, Shulamit, Christine D. Smart, Isaac Barash, Laura Chalupowicz, Guido Sessa y Thomas J. Burr. Clavibacter michiganensis subsp. michiganensis-tomato interactions: expression and function of virulence factors, plant defense responses and pathogen movement. United States Department of Agriculture, febrero de 2015. http://dx.doi.org/10.32747/2015.7594405.bard.

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Clavibactermichiganensissubsp. michiganensis(Cmm), the causal agent of bacterial wilt and canker of tomato, is the most destructive bacterial disease of tomato causing substantial economic losses in Israel, the U.S.A. and worldwide. The goal of the project was to unravel the molecular strategies that allow Cmm, a Gram-positive bacterium, to develop a successful infection in tomato. The genome of Cmm contains numerous genes encoding for extracellular serine proteases and cell wall degrading enzymes. The first objective was to elucidate the role of secreted serine proteases in Cmm virulence. Mutants of nine genes encoding serine proteases of 3 different families were tested for their ability to induce wilting, when tomato stems were puncture-inoculated, as compared to blisters formation on leaves, when plants were spray-inoculated. All the mutants showed reduction in wilting and blister formation as compared to the wild type. The chpCmutant displayed the highest reduction, implicating its major role in symptom development. Five mutants of cell wall degrading enzymes and additional genes (i.e. perforin and sortase) caused wilting but were impaired in their ability to form blisters on leaves. These results suggest that Cmm differentially expressed virulence genes according to the site of penetration. Furthermore, we isolated and characterized two Cmmtranscriptional activators, Vatr1 and Vatr2 that regulate the expression of virulence factors, membrane and secreted proteins. The second objective was to determine the effect of bacterial virulence genes on movement of Cmm in tomato plants and identify the routes by which the pathogen contaminates seeds. Using a GFP-labeledCmm we could demonstrate that Cmm extensively colonizes the lumen of xylem vessels and preferentially attaches to spiral secondary wall thickening of the protoxylem and formed biofilm-like structures composed of large bacterial aggregates. Our findings suggest that virulence factors located on the chp/tomAPAI or the plasmids are required for effective movement of the pathogen in tomato and for the formation of cellular aggregates. We constructed a transposon plasmid that can be stably integrated into Cmm chromosome and express GFP, in order to follow movement to the seeds. Field strains from New York that were stably transformed with this construct, could not only access seeds systemically through the xylem, but also externally through tomato fruit lesions, which harbored high intra-and intercellular populations. Active movement and expansion of bacteria into the fruit mesocarp and nearby xylem vessels followed, once the fruit began to ripen. These results highlight the ability of Cmm to invade tomato fruit and seed through multiple entry routes. The third objective was to assess correlation between disease severity and expression levels of Cmm virulence genes and tomato defense genes. The effect of plant age on expression of tomato defense related proteins during Cmm infection was analyzed by qRT-PCR. Five genes out of eleven showed high induction at early stages of infection of plants with 19/20 leaves compared to young plants bearing 7/8 leaves. Previous results showed that Cmm virulence genes were expressed at early stages of infection in young plants compared to older plants. Results of this study suggest that Cmm virulence genes may suppress expression of tomato defense-related genes in young plants allowing effective disease development. The possibility that chpCis involved in suppression of tomato defense genes is currently under investigation by measuring the transcript level of several PR proteins, detected previously in our proteomics study. The fourth objective was to define genome location and stability of virulence genes in Cmm strains. New York isolates were compared to Israeli, Serbian, and NCPPB382 strains. The plasmid profiles of New York isolates were diverse and differed from both Israeli and Serbian strains. PCR analysis indicated that the presence of putative pathogenicity genes varied between isolates and highlighted the ephemeral nature of pathogenicity genes in field populations of Cmm. Results of this project significantly contributed to the understanding of Cmm virulence, its movement within tomato xylem or externally into the seeds, the role of serine proteases in disease development and initiated research on global regulation of Cmm virulence. These results form a basis for developing new strategies to combat wilt and canker disease of tomato.
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Granot, David y Noel Michelle Holbrook. Role of Fructokinases in the Development and Function of the Vascular System. United States Department of Agriculture, enero de 2011. http://dx.doi.org/10.32747/2011.7592125.bard.

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Plant vascular tissues are superhighways whose development and function have profound implications for productivity, yield and stress response. Preliminary studies by the PI indicated that sugar metabolism mediated by fructokinases (FRKs) has a pronounced effect on the transport properties of the xylem. The goal of this research was to determine how the main fructokinase gene, FRK2, and the only plastidic fructokinase, FRK3, influence vascular development and physiology, emphasizing processes that occur at both the cellular and organismic level. We found that both genes are expressed in vascular tissues, but FRK3 is expressed primarily in vascular tissues of mature petioles. Vascular anatomy of plants with antisense suppression of FRK2 uncovered that FRK2 is necessary for xylem and phloem development, most likely due to its role in vascular cell-wall synthesis, and affects vascular development all over the plant. As a result, suppression of FRK2 reduced hydraulic conductivity of roots, stem and leaves and restricted sugar phloem transport. Vascular anatomy of plants with RNAi suppression of FRK3 uncovered that FRK3 is required for vascular development in mature petiole but its role is partially complemented by FRK2. Suppression of FRK3 combined with partial suppression of FRK2 had effects completely different from that of FRK2 suppression, resulting in wilting of mature leaves rather than young leaves of FRK2 suppressed plants, and decreased export of photoassimilates. This primary effect of FRK2 suppression on mature petioles had a secondary effect, reducing the hydraulic conductivity in roots and stem. The very fact that a plastidic fructokinase plays a role in vascular development is quite surprising and we are still seeking to uncover its metabolic mode-of-action. Yet, it is clear that these two fructokinases have different roles in the coordination between photosynthetic capacity and vascular development. We have started analyzing the role of the last third FRK, FRK1, and discovered that it is also expressed exclusively in vascular tissues. It appears therefore, that all FRKs studied here are involved in vascular development. An interesting unexpected outcome of this study was the connection of FRK2 with hormonal regulation of vascular development, most likely auxin. This observation together with the yet to be solved questions on the exact roles of FRK3 are the subjects of our current efforts.
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Meyerowitz, Elliot M. Regulation of plant cells, cell walls and development by mechanical signals. Office of Scientific and Technical Information (OSTI), junio de 2016. http://dx.doi.org/10.2172/1302424.

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Staehelin, A. 1997 Gordon Research Conference on Plant Cell Walls. Final progress report. Office of Scientific and Technical Information (OSTI), agosto de 1999. http://dx.doi.org/10.2172/764188.

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