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Diferenciação dos feixes vasculares e dos elementos traqueais no rizoma de algumas Cyperaceae; Differentiation of vascular bundles and tracheary elements in the rhizome of some Cyperaceae

RODRIGUES, Ana Claudia; ESTELITA, Maria Emília Maranhão
Fonte: Sociedade Botânica de São Paulo Publicador: Sociedade Botânica de São Paulo
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
37.752637%
Foram analisados os rizomas de Bulbostylis paradoxa Ness, Cyperus giganteus Vahl, C. odoratus L., Fuirena umbellata Rottb. e Hypolytrum schraderianum Ness. O corpo primário é resultante da atividade dos meristemas apicais e do meristema de espessamento primário (MEP). Também ocorre crescimento em espessura, que é decorrente da atividade do meristema de espessamento secundário (MES). O procâmbio e o MEP originam feixes colaterais em H. schraderianum e feixes anfivasais nas demais espécies. Entretanto, todos os feixes que têm protofloema e protoxilema são de origem procambial. O MES produz floema e xilema constituindo um tecido vascular único. Elementos de vaso foram encontrados na maioria dos caules em estrutura primária e secundária, com exceção de H. schraderianum que, na estrutura secundária, contém apenas traqueídes, informação que respalda a ocorrência de crescimento secundário nas Cyperaceae. Os elementos de vaso apresentam grande variação morfológica; em estrutura primária, geralmente são mais alongados, com apêndices. Os elementos de vaso do crescimento secundário são relativamente mais curtos, apresentam apêndices e ramificações.; Were analized the rhizomes of Bulbostylis paradoxa Ness, Cyperus giganteus Vahl...

Anatomia em Velloziaceae: caracteres, evolução e filogenia; Anaromy in Velloziaceae: charactes, evolution and phylogeny

Cattai, Marina Blanco
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 04/05/2007 Português
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Em Velloziaceae, a delimitação da família, subfamílias e gêneros é bastante controversa e as filogenias existentes são mal sustentadas. Considerando que os estudos anatômicos são extremamente importantes na delimitação de novas espécies, na classificação e em análises cladísticas de Velloziaceae, o presente trabalho tem como objetivo ampliar o conhecimento anatômico da raiz, do caule e da folha. Através de secções anatômicas e dissociação do xilema de vinte e cinco espécies da família e três representantes do grupo externo (Bromeliaceae, Cyclanthaceae e Pandanaceae) visa buscar novos caracteres a serem incorporados em análises cladísticas. O estudo dos elementos traqueais evidenciou a presença de placa de perfuração simples na raiz e uma grande diversidade de formas de elementos traqueais no caule, já que é possível observar, em uma mesma espécie, desde traqueídes muito longas, até elementos de vaso muito curtos. À exceção de Acanthochlamys bracteata, todas as espécies analisadas possuem traqueídes no caule, característica que confere vantagens às plantas que sofrem estresses uma vez que são mais resistentes à cavitação. Na folha, à exceção de Talbotia elegans que possui apenas traqueídes...

A estrutura da angiosperma endoparasita Pilostyles ulei (Apodanthaceae): interface e impacto no lenho de Mimosa spp; The structure of the endoparasite angiosperm Pilostyles ulei (Apodanthaceae): interface and impact on Mimosa ssp xylem

Amaral, Marina Milanello do
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/06/2007 Português
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Essa Dissertação de Mestrado é apresentada em três capítulos que originarão três futuras publicações. Os capítulos só não estão sob a forma de artigos porque, para isso, tanto texto como figuras teriam de ser reduzidos. Nosso intuito é apresentar o trabalho de forma mais pormenorizada, gerando assim uma discussão mais rica, que poderá posteriormente gerar outros trabalhos mais específicos. Pilostyles (Apodanthaceae) são angiospermas endoparasitas de caules de Fabaceae e um dos mais notáveis exemplos de redução do corpo vegetativo. Apesar da ocorrência de muitas espécies na América do Sul, os relatos concentram-se em espécies de outras regiões, como Estados Unidos, Austrália e Oriente Médio. Para aperfeiçoar a interpretação desse corpo vegetativo, o primeiro capítulo desse trabalho investiga anatomicamente Pilostyles ulei, uma espécie sul-americana, em três hospedeiros diferentes de Fabaceae: Mimosa foliolosa var. multipinna, M. maguirei (ambas com ocorrência em Minas Gerais) e M. setosa var. paludosa (com ocorrência na Bahia). São abordados a constituição e o posicionamento do corpo da parasita, bem como a plasticidade da zona de contato entre parasita e hospedeiro. Fragmentos de caules parasitados e saudáveis foram processados e proporcionaram observações principalmente em Microscopia Óptica (tanto colorações simples e duplas quanto testes histoquímicos e macerações) e Microscopia Confocal. As imagens produzidas a partir de ambos os tipos de microscopia foram usadas conjuntamente e reunidas para interpretar a estrutura tridimensional que a parasita adquire em seu hospedeiro. Além disso...

Isolation of a vascular cell wall-specific monoclonal antibody recognizing a cell polarity by using a phage display subtraction method

Shinohara, Naoki; Demura, Taku; Fukuda, Hiroo
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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Using a strategy consisting of (i) the isolation of cell walls from synchronously differentiating cells of Zinnia, (ii) the generation of mAbs with an antibody phage display method, and (iii) screening with a subtraction method, we isolated mAbs recognizing vascular development-specific cell wall components without prior antigen identification. One of the isolated mAbs, designated CN 8, recognized a cell wall component contained in the hemicellulosic fraction. Immunohistochemical analyses showed that the CN 8 epitope was localized to the cell wall of immature tracheary elements and xylem parenchyma cells. In immature tracheary elements, the CN 8 epitope had a polarized localization pattern regardless of whether the cells are formed as parts of vessels in situ or as single tracheary elements in vitro, suggesting that cell polarity autonomously formed on the cell wall may function in tracheary element differentiation.

Sucrose Phosphate Synthase Activity Rises in Correlation with High-Rate Cellulose Synthesis in Three Heterotrophic Systems1

Babb, V. Michelle; Haigler, Candace H.
Fonte: American Society of Plant Physiologists Publicador: American Society of Plant Physiologists
Tipo: Artigo de Revista Científica
Publicado em /11/2001 Português
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Based on work with cotton fibers, a particulate form of sucrose (Suc) synthase was proposed to support secondary wall cellulose synthesis by degrading Suc to fructose and UDP-glucose. The model proposed that UDP-glucose was then channeled to cellulose synthase in the plasma membrane, and it implies that Suc availability in cellulose sink cells would affect the rate of cellulose synthesis. Therefore, if cellulose sink cells could synthesize Suc and/or had the capacity to recycle the fructose released by Suc synthase back to Suc, cellulose synthesis might be supported. The capacity of cellulose sink cells to synthesize Suc was tested by analyzing the Suc phosphate synthase (SPS) activity of three heterotrophic systems with cellulose-rich secondary walls. SPS is a primary regulator of the Suc synthesis rate in leaves and some Suc-storing, heterotrophic organs, but its activity has not been previously correlated with cellulose synthesis. Two systems analyzed, cultured mesophyll cells of Zinnia elegans L. var. Envy and etiolated hypocotyls of kidney beans (Phaseolus vulgaris), contained differentiating tracheary elements. Cotton (Gossypium hirsutum L. cv Acala SJ-1) fibers were also analyzed during primary and secondary wall synthesis. SPS activity rose in all three systems during periods of maximum cellulose deposition within secondary walls. The Z. elegans culture system was manipulated to establish a tight linkage between the timing of tracheary element differentiation and rising SPS activity and to show that SPS activity did not depend on the availability of starch for degradation. The significance of these findings in regard to directing metabolic flux toward cellulose will be discussed.

In Situ Detection of nDNA Fragmentation during the Differentiation of Tracheary Elements in Higher Plants.

Mittler, R.; Lam, E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1995 Português
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Programmed cell death (pcd) is thought to occur during the autolysis of xylem vessels. Although several ultrastructural aspects of this differentiation process have been characterized, certain key aspects of this process remain unsolved. Here we demonstrate in pea (Pisum sativum) that nuclei of vessel elements undergoing pcd contain fragmented nDNA. This finding may provide evidence for the activation of a DNA degradation mechanism prior to the final disruption of the nucleus that occurs during the autolysis stage of this differentiation process. In situ detection of DNA fragmentation in nuclei of vessel elements undergoing pcd may therefore suggest that this death process involves the activation of a mechanism for DNA degradation, similar to that activated during apoptosis in animal cells. In addition, this differentiation process may serve as a useful positive control for the in situ detection of pcd in other developmental pathways and during the hypersensitive response of plants to avirulent pathogens.

Secondary cell-wall-specific glycoprotein(s) from French bean hypocotyls.

Wojtaszek, P; Bolwell, G P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1995 Português
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Specific labeling of secondary cell walls of tracheary elements and of xylary and phloem fibers has been observed when wheat germ agglutinin (WGA) and anti-WGA antibodies were used during ultrastructural studies of French bean (Phaseolus vulgaris L.) hypocotyls. In this report we demonstrate that at least part of this labeling is due to the presence of secondary cell-wall-specific glycoproteins. Three major novel glycoproteins with relative molecular weights of 55,000, 86,000, and 90,000, purified by means of WGA-Sepharose affinity chromatography, have been characterized. Their amino acid composition indicates that they are not the members of known classes of structural cell-wall proteins, since they contain no hydroxyproline, a lower level of glycine than seen in glycine-rich proteins, and very little proline. N-terminal sequences of all three proteins show no significant homology with other proteins. Antibodies were raised against electrophoretically pure 90-kD glycoprotein. These were used to localize this protein in secondary cell walls of xylem tracheary elements and in xylary and phloem fibers, i.e. in the same compartments where labeling with WGA has been observed. To our knowledge this is one of the first biochemical and ultrastructural demonstrations of secondary cell-wall-specific glycoproteins.

Cellular localization of Arabidopsis xyloglucan endotransglycosylase-related proteins during development and after wind stimulation.

Antosiewicz, D M; Purugganan, M M; Polisensky, D H; Braam, J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1997 Português
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A gene family encoding xyloglucan endotransglycosylase (XET)-related proteins exists in Arabidopsis. TCH4, a member of this family, is strongly up-regulated by environmental stimuli and encodes an XET capable of modifying cell wall xyloglucans. To investigate XET localization we generated antibodies against the TCH4 carboxyl terminus. The antibodies recognized TCH4 and possibly other XET-related proteins. These data indicate that XETs accumulate in expanding cell, at the sites of intercellular airspace formation, and at the bases of leaves, cotyledons, and hypocotyls. XETs also accumulated in vascular tissue, where cell wall modifications lead to the formation of tracheary elements and sieve tubes. Thus, XETs may function in modifying cell walls to allow growth, airspace formation, the development of vasculature, and reinforcement of regions under mechanical strain. Following wind stimulation, overall XET levels appeared to decrease in the leaves of wind-stimulated plants. However, consistent with an increase in TCH4 mRNA levels following wind, there were regions that showed increased immunoreaction, including sites around cells of the pith parenchyma, between the vascular elements, and within the epidermis. These results indicate that TCH4 may contribute to the adaptive changes in morphogenesis that occur in Arabidopsis following exposure to mechanical stimuli.

Novel vascular cell-specific genes whose expression is regulated temporally and spatially during vascular system development.

Demura, T; Fukuda, H
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1994 Português
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We have isolated three cDNA clones (TED2, TED3, and TED4) for genes expressed preferentially in cells that redifferentiate into tracheary elements from mesophyll cells isolated from leaves of Zinnia elegans. Sequence analyses of TED clones revealed that TED2 encodes a hydrophobic polypeptide with a significant similarity to the guinea pig lens-specific protein (zeta-crystallin) and that the deduced polypeptide of TED3 may be a novel cell wall protein. In situ hybridization of the TED probes with young Zinnia seedlings showed that expression of the three TED genes was restricted to vascular cells and regulated in a temporal and spatial manner during vascular development. TED3 transcripts were localized specifically to a few cells that are to differentiate or are differentiating into tracheary elements in all organs examined. TED4 transcripts were present mainly in the immature primary xylem both of cotyledons and of the boundary region between the root and hypocotyl and in the procambium of roots. In contrast, TED2 transcripts accumulated not only in immature primary xylem cells but also in immature phloem cells both in roots and in the boundary region between the root and hypocotyl. In addition, TED2 transcripts were expressed in the procambium cells of roots. In cotyledons...

Hormonal Control of Cell Proliferation and Xylem Differentiation in Cultured Tissues of Glycine max var. Biloxi 1

Fosket, D. E.; Torrey, J. G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1969 Português
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The relationship between tracheary element differentiation, cell proliferation and growth hormones was examined in agar-grown soybean callus. The time course of cell division and tracheary element formation in tissues grown on a medium containing 5 × 10−7m kinetin and 10−5m NAA was determined by means of maceration technique. After a slight lag period, a logarithmic increase in cell number was observed through the twelfth day of the culture period. Cell numbers increased at a considerably slower rate after the twelfth day. The rate of tracheary element formation varied with the rate of cell proliferation. Tracheary elements increased logarithmically during the log phase of growth. As the rate of cell division decreased after the twelfth day of culture, the rate of tracheary element formation also decreased. In the presence of 10−5m NAA, cell number increased as the kinetin concentration was increased between 10−9 and 10−6m. However, tracheary element formation was not initiated unless the kinetin concentration was 5 × 10−8m or above. When the Biloxi callus was subcultured repeatedly on media containing 10−8m kinetin, a tracheary element-free population of cells was obtained. This undifferentiated tissue produced tracheary elements upon transfer to a medium containing 5 × 10−7m kinetin. In the presence of 5 × 10−7m kinetin...

Programming of Cells for Death under Defined Experimental Conditions: Relevance to the Tumor Problem

Basile, Dominick V.; Wood, Henry N.; Braun, Armin C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1973 Português
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28.044014%
An attempt was made in this study to determine more precisely the nature of the factors that are involved in the programming of cells for a form of terminal cellular differentiation that results in death. These studies demonstrated that both the cytokinesins, which are potent inhibitors of plant and animal adenosine 3′:5′-cyclic monophosphate phosphodiesterases, and 8-bromoadenosine 3′:5′-cyclic monophosphate, which is a stable, biologically active form of adenosine 3′:5′-cyclic monophosphate, are highly effective in encouraging differentiation of parenchyma cells into tracheary elements with accompanying death. Since adenosine 3′:5′-cyclic monophosphate and theophylline when used together were also effective, the results reported here suggest that adenosine 3′:5′-cyclic monophosphate is somehow importantly involved in the conversion of parenchyma cells into tracheary elements in this system. The possible significance to the tumor problem generally of the programming of cells for terminal differentiation, with or without resulting death, is discussed.

The ATE Genes Are Responsible for Repression of Transdifferentiation into Xylem Cells in Arabidopsis1

Sawa, Shinichrio; Demura, Taku; Horiguchi, Gorou; Kubo, Minoru; Fukuda, Hiroo
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /01/2005 Português
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We isolated three recessive mutants of Arabidopsis (Arabidopsis thaliana) showing ectopic expression of the xylem-specific marker, pAtxyn3::YFP. Genetic analysis indicated that the phenotypes were caused by mutations in three different genes, designated Abnormal Tracheary Element formation-related gene expression (ate1–3). The ate1 mutants showed a normal DR5::GUS gene expression pattern, and the ate1 mutation did not affect the abnormal vascular pattern formation in the van3 and pin1 mutants, indicating that the ate1 mutation does not affect the vascular pattern organization governed by auxin. The ate mutants showed ectopic lignin deposition, patterned secondary wall thickenings, and cell death, which are characteristic of mature tracheary elements (TEs) in cells ectopically expressing the pAtxyn3::YFP gene. Ectopic TE formation was rapidly induced in parenchymal tissue of the ate mutants in a TE-inducible system with excised hypocotyl. Furthermore, reverse transcription-polymerase chain reaction experiments showed that the expression of TE formation-related genes is up-regulated in the ate mutants. The ate1 mutation also caused ectopic expression of another xylem-specific marker gene, pAt3g62160::YFP. Overall, our results suggest that the ATE genes are responsible for the in situ repression of transdifferentiation into TEs in Arabidopsis and could be participants in the transdifferentiation-masking system.

The NAC Transcription Factors NST1 and NST2 of Arabidopsis Regulate Secondary Wall Thickenings and Are Required for Anther DehiscenceW⃞

Mitsuda, Nobutaka; Seki, Motoaki; Shinozaki, Kazuo; Ohme-Takagi, Masaru
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /11/2005 Português
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In plants, secondary wall thickenings play important roles in various biological processes, although the factors regulating these processes remain to be characterized. We show that expression of chimeric repressors derived from NAC SECONDARY WALL THICKENING PROMOTING FACTOR1 (NST1) and NST2 in Arabidopsis thaliana resulted in an anther dehiscence defect due to loss of secondary wall thickening in anther endothecium. Plants with double, but not single, T-DNA–tagged lines for NST1 and NST2 had the same anther-indehiscent phenotype as transgenic plants that expressed the individual chimeric repressors, indicating that NST1 and NST2 are redundant in regulating secondary wall thickening in anther walls. The activity of the NST2 promoter was particularly strong in anther tissue, while that of the NST1 promoter was detected in various tissues in which lignified secondary walls develop. Ectopic expression of NST1 or NST2 induced ectopic thickening of secondary walls in various aboveground tissues. Epidermal cells with ectopic thickening of secondary walls had structural features similar to those of tracheary elements. However, among genes involved in the differentiation of tracheary elements, only those related to secondary wall synthesis were clearly upregulated. None of the genes involved in programmed cell death were similarly affected. Our results suggest NAC transcription factors as possible regulators of secondary wall thickening in various tissues.

The peripheral xylem of grapevine (Vitis vinifera) berries. 2. Anatomy and development

Chatelet, David S.; Rost, Thomas L.; Matthews, Mark A.; Shackel, Kenneth A.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
Português
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It has been hypothesized that the substantial reductions in xylemic water flow occurring at veraison are due to physical disruption (breaking) of the xylem as a result of renewed berry growth. In a companion paper, evidence was presented that the vast majority of xylem tracheary elements remained intact despite the growth of the berry, and it was proposed that existing tracheary elements stretch to accommodate growth and that additional elements may also differentiate after veraison. Measurements of the intergyre distance of tracheary elements in macerated tissue were used to test for stretching, and the numbers of tracheary elements per vascular bundle and of branch points of the peripheral xylem network were analysed to test for continued differentiation from 18 to 120 d after anthesis in Chardonnay berries. The distance between the epidermis and the vasculature increased substantially from pre- to post-veraison, potentially increasing the amount of skin available for analysis of compounds important for winemaking. Tracheary elements continued to differentiate within the existing vascular bundles throughout berry development. Additional vascular bundles also appeared until after veraison, thereby increasing the complexity of the peripheral vascular network. The results also confirmed that tracheary elements stretched by ∼20%...

The peripheral xylem of grapevine (Vitis vinifera). 1. Structural integrity in post-veraison berries

Chatelet, David S.; Rost, Thomas L.; Shackel, Kenneth A.; Matthews, Mark A.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
28.603296%
During the development of many fleshy fruits, water flow becomes progressively more phloemic and less xylemic. In grape (Vitis vinifera L.), the current hypothesis to explain this change is that the tracheary elements of the peripheral xylem break as a result of berry growth, rendering the xylem structurally discontinuous and hence non-functional. Recent work, however, has shown via apoplastic dye movement through the xylem of post-veraison berries that the xylem should remain structurally intact throughout berry development. To corroborate this, peripheral xylem structure in developing Chardonnay berries was investigated via maceration and plastic sectioning. Macerations revealed that, contrary to current belief, the xylem was comprised mostly of vessels with few tracheids. In cross-section, the tracheary elements of the vascular bundles formed almost parallel radial files, with later formed elements toward the epidermis and earlier formed elements toward the centre of the berry. Most tracheary elements remained intact throughout berry maturation, consistent with recent reports of vascular dye movement in post-veraison berries.

EXO70A1-Mediated Vesicle Trafficking Is Critical for Tracheary Element Development in Arabidopsis[W][OA]

Li, Shipeng; Chen, Min; Yu, Dali; Ren, Shichao; Sun, Shufeng; Liu, Linde; Ketelaar, Tijs; Emons, Anne-Mie C.; Liu, Chun-Ming
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
37.813896%
Genes encoding for EXO70, a component of the exocyst complex, are highly expanded in plant genomes, with reasons unknown. EXO70A1 expressed primarily in tracheary elements regulates vesicle trafficking during xylem formation, suggesting that individual EXO70 members in plants may act in cell type– or cargo-specific exocytosis.

Syringyl lignin production in conifers: Proof of concept in a Pine tracheary element system

Wagner, Armin; Tobimatsu, Yuki; Phillips, Lorelle; Flint, Heather; Geddes, Barbara; Lu, Fachuang; Ralph, John
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
37.813896%
This study shows that metabolic engineering can be used to imbue pine tracheary elements with an ability to synthesize sinapyl alcohol, a lignin monomer not normally used for lignification in conifers such as pine. The dynamic nature of the lignification process enables pines to incorporate this monolignol, allowing them to produce hardwood-like lignins that are known to facilitate refining processes such as biofuel production and chemical pulping. The potential to improve the refining of conifer-derived biomass through lignin manipulations is important, as even small improvements in yield can lead to significant environmental and economic benefits in such processes.

Specific Peroxidase Isoenzymes Are Correlated with Organogenesis 1

Kay, Lou Ellen; Basile, Dominick V.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1987 Português
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We have examined isoperoxidase patterns obtained from buffer-, salt-, and enzyme-extractable fractions and correlated them with histological changes in tobacco (Nicotiana tabacum L., cv Wisc. 38) `epidermal' explants induced to produce either callus, vegetative buds, or floral buds. By utilizing a combination of extraction and electrophoretic procedures different from any hitherto used for this kind of investigation, we were able to resolve 47 isoperoxidases distributed between the three types of fractions. The majority of these isoperoxidases were common to all explants regardless of their developmental fate. Correspondingly, a number of histological changes were observed in all explants (e.g. the initiation of cell division by day 2, lignin deposition by day 4, and the formation of clustered tracheary elements by day 8). We have made correlations between 25 isoperoxidases and specific developmental events based on the time when certain isoperoxidases were detected relative to observed histological changes: 3 were correlated with desuppressed/sustained cell division, 3 to 6 with lignification/tracheary element maturation, 7 with callus formation, 1 with localized suppression of growth, 3 with determinate axial organization, 4 with leaf development...

Identifying New Components Participating in the Secondary Cell Wall Formation of Vessel Elements in Zinnia and Arabidopsis[W]

Endo, Satoshi; Pesquet, Edouard; Yamaguchi, Masatoshi; Tashiro, Gen; Sato, Mayuko; Toyooka, Kiminori; Nishikubo, Nobuyuki; Udagawa-Motose, Makiko; Kubo, Minoru; Fukuda, Hiroo; Demura, Taku
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /04/2009 Português
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Xylem vessel elements are hollow cellular units that assemble end-to-end to form a continuous vessel throughout the plant body; the xylem vessel is strengthened by the xylem elements' reinforced secondary cell walls (SCWs). This work aims to unravel the contribution of unknown actors in xylem vessel differentiation using the model in vitro cell culture system of Zinnia elegans differentiating cell cultures and the model in vivo system of Arabidopsis thaliana plants. Tracheary Element Differentiation-Related6 (TED6) and TED7 were selected based on an RNA interference (RNAi) screen in the Zinnia system. RNAi reduction of TED6 and 7 delayed tracheary element (TE) differentiation and co-overexpression of TED6 and 7 increased TE differentiation in cultured Zinnia cells. Arabidopsis TED6 and 7 were expressed preferentially in differentiating vessel elements in seedlings. Aberrant SCW formation of root vessel elements was induced by transient RNAi of At TED7 alone and enhanced by inhibition of both TED6 and 7. Protein–protein interactions were demonstrated between TED6 and a subunit of the SCW-related cellulose synthase complex. Our strategy has succeeded in finding two novel components in SCW formation and has opened the door for in-depth analysis of their molecular functions.

Osmosis at constant volume and water uptake in tall trees

Zupanovic, Pasko; Brumen, Milan; Fajmut, Ales; Kuic, Domagoj; Juretic, Davor
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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We consider a thermodynamic state of a solvent and solution separated with an elastic semipermeable membrane in a box with a constant volume and the relevance of this simple model for the water uptake in tall trees. Under moderate concentrations of a solute, the solution and solvent are under the positive and negative pressure, respectively. In the case of the soft membrane the pressure difference between the compartments with the solvent and solution is given by van't Hoff equation. A state of the negative pressure is not stable and after some time cavitations transform the solvent into the state of coexisting liquid and bubbles of saturated vapor. The pressure difference between the solvent and solution decreases and the membrane relaxes restoring the liquid phase in the compartment with solvent. In this way the solvent oscillates between the tensile state and the coexisting state of liquid and bubbles of saturated vapor. The xylem and phloem, the main vascular systems in trees, are coupled with ray cells. Assuming that a sap in these systems is kept under the constant volume the osmosis between the xylem and phloem with ray cells sustains the negative pressure of the xylem sap. Due to the osmosis elastic energy stored in walls of tracheary element could repair cavitations. In this way both water transport in tall trees and cavitations repair in tracheary elements are related to the osmosis under constant volume. A possible explanation of two long standing problems in tree physiology...