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1.
Chemosphere ; 233: 920-935, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31340420

RESUMO

The current study aimed to investigate the impacts of different concentrations of GO/PANI nanocomposites (25, 50 and 100 mg L-1), in comparison with GO and PANI, on seed germination behaviors, morpho-physiological and biochemical traits in intact (mucilaginous) and demucilaged seeds, and young seedlings of the medicinal plant Salvia mirzayanii. Upon exposure to GO, seed germination was delayed and reduced, and growth attributes (root and shoot length, shoot fresh weight, and total chlorophyll content) declined, all of which could be attributed to the reductions in water uptake and oxidative stress particularly in demucilaged seeds. A hormetic dose-dependent response was observed for the growth traits in both intact and demucilaged seedlings upon exposure to GO/PANI concentrations, i.e. low-concentration stimulation and high-concentration repression. Elevated levels of H2O2 in shoot tissue of the seedlings exposed to GO and high concentration of GO/PANI, in comparison with those exposed to low levels of GO/PANI and control, were linked with the activities of the antioxidant enzymes SOD, CAT, POD, and total phenolics. Overall, the results showed high toxicity of GO on germination and early growth of S. mirzayani that was more evident in demucilaged seedlings, whereas GO/PANI stimulated germination, and the effects on seedling growth were stimulatory or inhibitory depending on the application dose and presence of mucilage. Furthermore, the capacity of GO/PANI nanocomposites to improve germination and cause a regular porosity pattern in roots accompanied by improved water uptake and early establishment of S. mirzayanii propose potential implications of GO/PANI nanocomposites for seeds/plants in drought-prone ecosystems.


Assuntos
Compostos de Anilina/toxicidade , Antioxidantes/farmacologia , Germinação/efeitos dos fármacos , Grafite/toxicidade , Salvia/metabolismo , Plântula/crescimento & desenvolvimento , Sementes/efeitos dos fármacos , Catalase/metabolismo , Clorofila , Peróxido de Hidrogênio/farmacologia , Nanocompostos , Estresse Oxidativo/efeitos dos fármacos , Mucilagem Vegetal/metabolismo , Superóxido Dismutase/metabolismo , Água
2.
Plant Cell Physiol ; 60(6): 1296-1303, 2019 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-30892660

RESUMO

Plant roots secrete various substances with diverse functions against both plants and microbes in the rhizosphere. A major secretory substance is root-cap mucilage, whose functions have been well characterized, albeit mainly in crops. However, little is currently known about the developmental mechanisms of root-cap mucilage. Here, we show the accumulation and extrusion of root-cap mucilage in Arabidopsis. We found propidium iodide (PI) stainable structures between the plasma membrane and cell wall in the sixth layer of columella cells (c6) from the quiescent center. Ruthenium red staining and PI staining with calcium ions suggested that the structure comprises in part pectin polysaccharides. Electron microscopy revealed that the structure had a meshwork of electron-dense filaments that resembled periplasmic mucilage in other plants. In the c6 cells, we also observed many large vesicles with denser meshwork filaments to periplasmic mucilage, which likely mediate the transport of mucilage components. Extruded mucilage was observed outside a partially degraded cell wall in the c7 cells. Moreover, we found that the Class IIB NAC transcription factors BEARSKIN1 (BRN1) and BRN2, which are known to regulate the terminal differentiation of columella cells, were required for the efficient accumulation of root-cap mucilage in Arabidopsis. Taken together, our findings reveal the accumulation of and dynamic changes in periplasmic mucilage during columella cell development in Arabidopsis.


Assuntos
Arabidopsis/crescimento & desenvolvimento , Periplasma/metabolismo , Mucilagem Vegetal/metabolismo , Coifa/metabolismo , Arabidopsis/citologia , Arabidopsis/metabolismo , Arabidopsis/ultraestrutura , Corantes , Microscopia Eletrônica de Transmissão , Coifa/citologia , Coifa/ultraestrutura , Propídio
3.
Plant Physiol Biochem ; 139: 191-196, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30904720

RESUMO

Pea (Pisum sativum) root cap releases a large number of living border cells that secrete abundant mucilage into the extracellular medium. Mucilage contains a complex mixture of polysaccharides, proteins and secondary metabolites important for its structure and function in defense. Unlike xyloglucan and cellulose, pectin and arabinogalactan proteins have been investigated in pea root and shown to be major components of border cell walls and mucilage. In this study, we investigated the occurrence of xyloglucan and cellulose in pea border cells and mucilage using cytochemical staining, immunocytochemistry and laser scanning confocal microscopy. Our data show that i) unlike cellulose, xyloglucan is highly present in the released mucilage as a dense fibrillary network enclosing border cells and ii) that xyloglucan and cellulose form molecular cross-bridges that tether cells and maintain them attached together. These findings suggest that secreted xyloglucan is essential for mucilage strengthening and border cell attachment and functioning.


Assuntos
Celulose/metabolismo , Glucanos/metabolismo , Ervilhas/metabolismo , Raízes de Plantas/citologia , Xilanos/metabolismo , Microscopia Confocal , Ervilhas/ultraestrutura , Mucilagem Vegetal/metabolismo , Coifa/citologia , Coifa/metabolismo , Raízes de Plantas/metabolismo , Raízes de Plantas/ultraestrutura
4.
Plant Mol Biol ; 99(4-5): 421-436, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30707395

RESUMO

KEY MESSAGE: A possible transcription factor TLP2 was identified to be involved in the regulation of HG biosynthesis in Arabidopsis seed mucilage. TLP2 can translocate into nucleus from plasma membrane by interacting with NF-YC3. The discovery of TLP2 gene function can further fulfill the regulatory network of pectin biosynthesis in Arabidopsis thaliana. Arabidopsis seed coat mucilage is an excellent model system to study the biosynthesis, function and regulation of pectin. Rhamnogalacturonan I (RG-I) and homogalacturonan (HG) are the major polysaccharides constituent of the Arabidopsis seed coat mucilage. Here, we identified a Tubby-like gene, Tubby-like protein 2 (TLP2), which was up-regulated in developing siliques when mucilage began to be produced. Ruthenium red (RR) staining of the seeds showed defective mucilage of tlp2-1 mutant after vigorous shaking compared to wild type (WT). Monosaccharide composition analysis revealed that the amount of total sugars and galacturonic acid (GalA) decreased significantly in the adherent mucilage (AM) of tlp2-1 mutant. Immunolabelling and dot immunoblotting analysis showed that unesterified HG decreased in the tlp2-1 mutant. Furthermore, TLP2 can translocate into nucleus by interacting with Nuclear Factor Y subunit C3 (NF-YC3) to function as a transcription factor. RNA-sequence and transactivation assays revealed that TLP2 could activate UDP-glucose 4-epimerase 1 (UGE1). In all, it is concluded that TLP2 could regulate the biosynthesis of HG possibly through the positive activation of UGE1.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Pectinas/biossíntese , Mucilagem Vegetal/metabolismo , Sementes/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas F-Box/genética , Proteínas F-Box/metabolismo , Regulação da Expressão Gênica de Plantas , Ácidos Hexurônicos , Mutação , Fenótipo , Plantas Geneticamente Modificadas , Polissacarídeos , Sementes/crescimento & desenvolvimento , Análise de Sequência de RNA , Fatores de Transcrição , Ativação Transcricional , Uridina Difosfato Glucose Desidrogenase/metabolismo
5.
Plant Cell Physiol ; 59(11): 2331-2338, 2018 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-30099531

RESUMO

The adaptor protein (AP) complexes play crucial roles in vesicle formation in post-Golgi trafficking. Land plants have five types of AP complexes (AP-1 to AP-5), each of which consists of two large subunits, one medium subunit and one small subunit. Here, we show that the Arabidopsis AP-1 complex mediates the polarized secretion and accumulation of a pectic polysaccharide called mucilage in seed coat cells. Previously, a loss-of-function mutant of AP1M2, the medium subunit of AP-1, has been shown to display deleterious growth defects because of defective cytokinesis. To investigate the function of AP-1 in interphase, we generated transgenic Arabidopsis plants expressing AP1M2-GFP (green fluorescent protein) under the control of the cytokinesis-specific KNOLLE (KN) promoter in the ap1m2 background. These transgenic plants, designated pKN lines, successfully rescued the cytokinesis defect and dwarf phenotype of ap1m2. pKN lines showed reduced mucilage extrusion from the seed coat. Furthermore, abnormal accumulation of mucilage was found in the vacuoles of the outermost integument cells of pKN lines. During seed development, the accumulation of AP1M2-GFP was greatly reduced in the integument cells of pKN lines. These results suggest that trans-Golgi network (TGN)-localized AP-1 is involved in the trafficking of mucilage components to the outer surface of seed coat cells. Our study highlights an evolutionarily conserved function of AP-1 in polarized sorting in eukaryotic cells.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Mucilagem Vegetal/biossíntese , Sementes/metabolismo , Fator de Transcrição AP-1/metabolismo , Regulação da Expressão Gênica de Plantas , Mucilagem Vegetal/metabolismo , Regiões Promotoras Genéticas , Rede trans-Golgi/metabolismo
6.
Plant Sci ; 272: 179-192, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-29807590

RESUMO

A polysaccharide-rich mucilage is released from the seed coat epidermis of numerous plant species and has been intensively studied in the model plant Arabidopsis. This has led to the identification of a large number of genes involved in the synthesis, secretion and modification of cell wall polysaccharides such as pectin, hemicellulose and cellulose being identified. These genes include a small network of transcription factors (TFs) and transcriptional co-regulators, that not only regulate mucilage production, but epidermal cell differentiation and in some cases flavonoid biosynthesis in the internal endothelial layer of the seed coat. Here we focus on the function of these regulators and propose a simplified model where they are assigned to a hierarchical gene network with three regulatory levels (tiers) as a means of assisting in the interpretation of the complexity. We discuss limitations of current methodologies and highlight some of the problems associated with defining the function of TFs, particularly those that perform different functions in adjacent layers of the seed coat. We suggest approaches that should provide a more accurate picture of the function of transcription factors involved with mucilage production and release.


Assuntos
Arabidopsis/metabolismo , Mucilagem Vegetal/metabolismo , Sementes/metabolismo , Fatores de Transcrição/fisiologia , Regulação da Expressão Gênica de Plantas/fisiologia
7.
Protoplasma ; 255(3): 911-921, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29270874

RESUMO

Diatoms stand out among other microalgae due to the high diversity of species-specific silica frustules whose components (valves and girdle bands) are formed within the cell in special organelles called silica deposition vesicles (SDVs). Research on cell structure and morphogenesis of frustule elements in diatoms of different taxonomic groups has been carried out since the 1950s but is still relevant today. Here, cytological features and valve morphogenesis in the freshwater raphid pennate diatom Encyonema ventricosum (Agardh) Grunow have been studied using light and transmission electron microscopy of cleaned frustules and ultrathin sections of cells, and scanning electron and atomic force microscopy of the frustule surface. Data have been obtained on chloroplast structure: the pyrenoid is spherical, penetrated by a lamella (a stack of two thylakoids); the girdle lamella consists of several short lamellae. The basic stages of frustule morphogenesis characteristic of raphid pennate diatoms have been traced, with the presence of cytoskeletal elements near SDVs being observed throughout this process. Degradation of the plasmalemma and silicalemma is shown to take place when the newly formed valve is released into the space between sister cells. The role of vesicular transport and exocytosis in the gliding of pennate diatoms is discussed.


Assuntos
Diatomáceas/citologia , Diatomáceas/crescimento & desenvolvimento , Morfogênese , Cloroplastos/metabolismo , Cloroplastos/ultraestrutura , Diatomáceas/ultraestrutura , Mucilagem Vegetal/metabolismo
8.
Plant Cell Rep ; 37(4): 565-574, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29188422

RESUMO

Climbing plants have unique adaptations to enable them to compete for sunlight, for which they invest minimal resources for vertical growth. Indeed, their stems bear relatively little weight, as they traverse their host substrates skyward. Climbers possess high tensile strength and flexibility, which allows them to utilize natural and manmade structures for support and growth. The climbing strategies of plants have intrigued scientists for centuries, yet our understanding about biochemical adaptations and their molecular undergirding is still in the early stages of research. Nonetheless, recent discoveries are promising, not only from a basic knowledge perspective, but also for bioinspired product development. Several adaptations, including nanoparticle and adhesive production will be reviewed, as well as practical translation of these adaptations to commercial applications. We will review the botanical literature on the modes of adaptation to climb, as well as specialized organs-and cellular innovations. Finally, recent molecular and biochemical data will be reviewed to assess the future needs and new directions for potential practical products that may be bioinspired by climbing plants.


Assuntos
Adaptação Fisiológica/fisiologia , Cálcio/metabolismo , Glicosaminoglicanos/metabolismo , Plantas/metabolismo , Luz Solar , Fenômenos Biomecânicos , Modelos Biológicos , Folhas de Planta/metabolismo , Folhas de Planta/fisiologia , Mucilagem Vegetal/metabolismo , Plantas/classificação , Tricomas/fisiologia
9.
Methods Mol Biol ; 1560: 313-330, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28155165

RESUMO

Histochemical analysis is essential for the study of plant secretory structures whose classification is based, at least partially, on the composition of their secretion. As each gland may produce one or more types of substances, a correct analysis of its secretion should be done using various histochemical tests to detect metabolites of different chemical classes. Here I describe some of the most used methods to detect carbohydrates, proteins, lipids, phenolic compounds, and alkaloids in the secretory structures.


Assuntos
Histocitoquímica/métodos , Células Vegetais/metabolismo , Estruturas Vegetais/citologia , Plantas/metabolismo , Metabolismo dos Carboidratos , Carboidratos/química , Mucilagem Vegetal/química , Mucilagem Vegetal/metabolismo , Proteínas de Plantas/química , Proteínas de Plantas/metabolismo , Metabolismo Secundário , Amido/química , Amido/metabolismo
10.
New Phytol ; 214(3): 959-966, 2017 May.
Artigo em Inglês | MEDLINE | ID: mdl-28191645

RESUMO

The cell wall defines the shape of cells and ultimately plant architecture. It provides mechanical resistance to osmotic pressure while still being malleable and allowing cells to grow and divide. These properties are determined by the different components of the wall and the interactions between them. The major components of the cell wall are the polysaccharides cellulose, hemicellulose and pectin. Cellulose biosynthesis has been extensively studied in Arabidopsis hypocotyls, and more recently in the mucilage-producing epidermal cells of the seed coat. The latter has emerged as an excellent system to study cellulose biosynthesis and the interactions between cellulose and other cell wall polymers. Here we review some of the major advances in our understanding of cellulose biosynthesis in the seed coat, and how mucilage has aided our understanding of the interactions between cellulose and other cell wall components required for wall cohesion. Recently, 10 genes involved in cellulose or hemicellulose biosynthesis in mucilage have been identified. These discoveries have helped to demonstrate that xylan side-chains on rhamnogalacturonan I act to link this pectin directly to cellulose. We also examine other factors that, either directly or indirectly, influence cellulose organization or crystallization in mucilage.


Assuntos
Arabidopsis/metabolismo , Parede Celular/metabolismo , Celulose/biossíntese , Mucilagem Vegetal/metabolismo , Polissacarídeos/metabolismo , Sementes/metabolismo , Arabidopsis/genética
11.
Plant Physiol ; 173(2): 1059-1074, 2017 02.
Artigo em Inglês | MEDLINE | ID: mdl-28003327

RESUMO

Plant cell wall proteins are important regulators of cell wall architecture and function. However, because cell wall proteins are difficult to extract and analyze, they are generally poorly understood. Here, we describe the identification and characterization of proteins integral to the Arabidopsis (Arabidopsis thaliana) seed coat mucilage, a specialized layer of the extracellular matrix composed of plant cell wall carbohydrates that is used as a model for cell wall research. The proteins identified in mucilage include those previously identified by genetic analysis, and several mucilage proteins are reduced in mucilage-deficient mutant seeds, suggesting that these proteins are genuinely associated with the mucilage. Arabidopsis mucilage has both nonadherent and adherent layers. Both layers have similar protein profiles except for proteins involved in lipid metabolism, which are present exclusively in the adherent mucilage. The most abundant mucilage proteins include a family of proteins named TESTA ABUNDANT1 (TBA1) to TBA3; a less abundant fourth homolog was named TBA-LIKE (TBAL). TBA and TBAL transcripts and promoter activities were detected in developing seed coats, and their expression requires seed coat differentiation regulators. TBA proteins are secreted to the mucilage pocket during differentiation. Although reverse genetics failed to identify a function for TBAs/TBAL, the TBA promoters are highly expressed and cell type specific and so should be very useful tools for targeting proteins to the seed coat epidermis. Altogether, these results highlight the mucilage proteome as a model for cell walls in general, as it shares similarities with other cell wall proteomes while also containing mucilage-specific features.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Mucilagem Vegetal/metabolismo , Sementes/metabolismo , Sequência de Aminoácidos , Arabidopsis/genética , Proteínas de Arabidopsis/química , Parede Celular/metabolismo , Regulação para Baixo/genética , Regulação da Expressão Gênica de Plantas , Epiderme Vegetal/metabolismo , Regiões Promotoras Genéticas/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo
12.
J Exp Bot ; 67(22): 6481-6495, 2016 12.
Artigo em Inglês | MEDLINE | ID: mdl-27856710

RESUMO

Xylans are the most abundant non-cellulosic polysaccharide found in plant cell walls. A diverse range of xylan structures influence tissue function during growth and development. Despite the abundance of xylans in nature, details of the genes and biochemical pathways controlling their biosynthesis are lacking. In this study we have utilized natural variation within the Plantago genus to examine variation in heteroxylan composition and structure in seed coat mucilage. Compositional assays were combined with analysis of the glycosyltransferase family 61 (GT61) family during seed coat development, with the aim of identifying GT61 sequences participating in xylan backbone substitution. The results reveal natural variation in heteroxylan content and structure, particularly in P. ovata and P. cunninghamii, species which show a similar amount of heteroxylan but different backbone substitution profiles. Analysis of the GT61 family identified specific sequences co-expressed with IRREGULAR XYLEM 10 genes, which encode putative xylan synthases, revealing a close temporal association between xylan synthesis and substitution. Moreover, in P. ovata, several abundant GT61 sequences appear to lack orthologues in P. cunninghamii. Our results indicate that natural variation in Plantago species can be exploited to reveal novel details of seed coat development and polysaccharide biosynthetic pathways.


Assuntos
Glicosiltransferases/metabolismo , Mucilagem Vegetal/metabolismo , Plantago/fisiologia , Sementes/fisiologia , Glicosiltransferases/genética , Microscopia , Microscopia Eletrônica de Varredura , Filogenia , Mucilagem Vegetal/análise , Plantago/enzimologia , Plantago/genética , Plantago/metabolismo , Reação em Cadeia da Polimerase , Sementes/química , Sementes/enzimologia , Sementes/crescimento & desenvolvimento
13.
Food Microbiol ; 59: 176-89, 2016 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-27375258

RESUMO

Strains of Leuconostoc mesenteroides were identified from raw prickly pear (Opuntia ficus-indica L.). Five autochthonous strains were selected based on the kinetics of growth and acidification on prickly pear fruit juice, and the capacity to synthesize exo-polysaccharides. All selected Leuc. mesenteroides strains showed an in vitro mucilage-degrading capability. A protocol for processing and storage of fermented prickly pear fruit puree (FP) was set up. Unstarted FP and chemically acidified FP were used as the controls. Starters grew and remained viable at elevated cell numbers during 21 days of storage at 4 °C. Contaminating Enterobacteriaceae and yeasts were found only in the controls. Viscosity and serum separation distinguished started FP compared to the controls. Colour parameters, browning index, sensory attributes, antimicrobial activity, vitamin C and betalains levels were positively affected by lactic acid fermentation. Increase of free radical scavenging activity in ethyl acetate soluble extract suggested an effect of selected strains on phenolic profiles. Started FP markedly inhibited the inflammatory status of Caco-2/TC7 cells, and also contributed to maintaining the integrity of tight junctions. Started FP scavenged the reactive oxygen species generated by H2O2 on Caco-2 cells. All selected strain variously affected the immunomodulatory activity towards anti- and pro-inflammatory cytokines.


Assuntos
Armazenamento de Alimentos , Frutas , Leuconostoc mesenteroides/isolamento & purificação , Leuconostoc mesenteroides/metabolismo , Opuntia , Antioxidantes , Células CACO-2 , Enterobacteriaceae/metabolismo , Fermentação , Conservação de Alimentos/métodos , Frutas/microbiologia , Sucos de Frutas e Vegetais/análise , Sucos de Frutas e Vegetais/microbiologia , Alimento Funcional , Humanos , Peróxido de Hidrogênio/metabolismo , Imunomodulação , Ácido Láctico/metabolismo , Leuconostoc mesenteroides/crescimento & desenvolvimento , Opuntia/microbiologia , Mucilagem Vegetal/metabolismo
14.
Plant Physiol Biochem ; 104: 278-83, 2016 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-27163609

RESUMO

A comparative study of mucilage (locular tissue) and pulp polysaccharides from ripe tamarillo fruits (Solanum betaceum Cav.) was carried out. After aqueous and alkaline extractions and various purification steps (freeze-thaw and α-amylase - EC 3.2.1.1 treatments, Fehling precipitation and ultrafiltration through 50 kDa cut-off membrane), the obtained fractions from mucilage were analyzed by sugar composition, HPSEC, and NMR spectroscopy analyses. The results showed that the mucilage of tamarillo contains a highly methoxylated homogalacturonans mixed with type I arabinogalactans, a linear (1 â†’ 5)-linked α-L-arabinan, and a linear (1 â†’ 4)-ß-D-xylan. A comparison with polysaccharides extracted from the pulp revealed that differences were observed in the yield and in the ratio of extracted polysaccharides. Moreover, structural differences between pulp and mucilage polysaccharides were also observed, such as in the length of side chains of the pectins, and in the degree of branching of the xylans.


Assuntos
Frutas/metabolismo , Mucilagem Vegetal/metabolismo , Polissacarídeos/metabolismo , Solanum/metabolismo , Espectroscopia de Ressonância Magnética Nuclear de Carbono-13 , Fracionamento Químico , Cromatografia em Gel , Monossacarídeos/análise , Pectinas/isolamento & purificação , Polissacarídeos/isolamento & purificação , Solubilidade , Água/química
15.
Plant Physiol ; 171(1): 165-78, 2016 05.
Artigo em Inglês | MEDLINE | ID: mdl-26979331

RESUMO

Arabidopsis (Arabidopsis thaliana) seed coat epidermal cells produce large amounts of mucilage that is released upon imbibition. This mucilage is structured into two domains: an outer diffuse layer that can be easily removed by agitation and an inner layer that remains attached to the outer seed coat. Both layers are composed primarily of pectic rhamnogalacturonan I (RG-I), the inner layer also containing rays of cellulose that extend from the top of each columella. Perturbation in cellulosic ray formation has systematically been associated with a redistribution of pectic mucilage from the inner to the outer layer, in agreement with cellulose-pectin interactions, the nature of which remained unknown. Here, by analyzing the outer layer composition of a series of mutant alleles, a tight proportionality of xylose, galacturonic acid, and rhamnose was evidenced, except for mucilage modified5-1 (mum5-1; a mutant showing a redistribution of mucilage pectin from the inner adherent layer to the outer soluble one), for which the rhamnose-xylose ratio was increased drastically. Biochemical and in vitro binding assay data demonstrated that xylan chains are attached to RG-I chains and mediate the adsorption of mucilage to cellulose microfibrils. mum5-1 mucilage exhibited very weak adsorption to cellulose. MUM5 was identified as a putative xylosyl transferase recently characterized as MUCI21. Together, these findings suggest that the binding affinity of xylose ramifications on RG-I to a cellulose scaffold is one of the factors involved in the formation of the adherent mucilage layer.


Assuntos
Arabidopsis/metabolismo , Parede Celular/metabolismo , Regulação da Expressão Gênica de Plantas , Mucilagem Vegetal/genética , Mucilagem Vegetal/metabolismo , Sementes/metabolismo , Xilanos/metabolismo , Arabidopsis/enzimologia , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Parede Celular/química , Celulose/metabolismo , Análise por Conglomerados , Genes de Plantas , Ligação Genética , Glucosiltransferases/genética , Glucosiltransferases/metabolismo , Ácidos Hexurônicos/metabolismo , Mutação , Pectinas/química , Pectinas/metabolismo , Extratos Vegetais/química , Mucilagem Vegetal/química , Ramnose/metabolismo , Sementes/enzimologia , Análise de Sequência de DNA , Coloração e Rotulagem , Xilanos/química , Xilose/metabolismo
16.
J Exp Bot ; 67(8): 2177-90, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26895630

RESUMO

Pectins are major components of plant primary cell walls. They include homogalacturonans (HGs), which are the most abundant pectin and can be the target of apoplastic enzymes like pectin methylesterases (PMEs) that control their methylesterification level. Several PMEs are expressed in the seed coat of Arabidopsis thaliana, particularly in mucilage secretory cells (MSCs). On the basis of public transcriptomic data, seven PME genes were selected and checked for their seed-specific expression by quantitative reverse transcription PCR. Of these, PME58 presented the highest level of expression and was specifically expressed in MSCs at the early stages of seed development. pme58 mutants presented two discrete phenotypes: (i) their adherent mucilage was less stained by ruthenium red when compared to wild-type seeds, but only in the presence of EDTA, a Ca(2+)chelator; and (ii) the MSC surface area was decreased. These phenotypes are the consequence of an increase in the degree of HG methylesterification connected to a decrease in PME activity. Analysis of the sugar composition of soluble and adherent mucilage showed that, in the presence of EDTA, sugars of adherent mucilage were more readily extracted in pme58 mutants. Immunolabelling with LM19, an antibody that preferentially recognizes unesterified HGs, also showed that molecular interactions with HGs were modified in the adherent mucilage of pme58 mutants, suggesting a role of PME58 in mucilage structure and organization. In conclusion, PME58 is the first PME identified to play a direct role in seed mucilage structure.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Hidrolases de Éster Carboxílico/metabolismo , Pectinas/metabolismo , Mucilagem Vegetal/metabolismo , Sementes/metabolismo , Arabidopsis/genética , Arabidopsis/ultraestrutura , Proteínas de Arabidopsis/genética , Hidrolases de Éster Carboxílico/genética , DNA Bacteriano/genética , Esterificação , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Mutagênese Insercional , Mutação/genética , Fenótipo , Mucilagem Vegetal/ultraestrutura , Regiões Promotoras Genéticas/genética , Sementes/genética , Sementes/crescimento & desenvolvimento , Sementes/ultraestrutura
17.
J Exp Bot ; 67(5): 1243-57, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-26834178

RESUMO

During differentiation, the Arabidopsis seed coat epidermal cells synthesize and secrete large quantities of pectinaceous mucilage into the apoplast, which is then released to encapsulate the seed upon imbibition. In this study, we showed that mutation in Irregular Xylem 14 (IRX14) led to a mucilage cohesiveness defect due to a reduced xylan content. Expression of IRX14 was detected specifically in the seed coat epidermal cells, reaching peak expression at 13 days post-anthesis (DPA) when the accumulation of mucilage polysaccharides has ceased. Sectioning of the irx14-1 seed coat revealed no visible structural change in mucilage secretory cell morphology. Although the total amount of mucilage was comparable with the wild type (WT), the partition between water-soluble and adherent layers was significantly altered in irx14-1, with redistribution from the adherent layer to the water-soluble layer. The monosaccharide composition analysis revealed that xylose content was significantly reduced in irx14-1 water-soluble and adherent mucilage compared with the WT. The macromolecular characteristics of the water-soluble mucilage were modified in irx14-1 with a loss of the larger polymeric components. In accordance, glycome profiling and dot immunoblotting of seed mucilage using antibodies specific for rhamnogalacturonan I (RG I) and xylan confirmed the ultra-structural alterations in the irx14-1 mucilage. Meanwhile, the crystalline cellulose content was reduced in the irx14-1 mucilage. These results demonstrated that IRX14 was required for the biosynthesis of seed mucilage xylan, which plays an essential role in maintaining mucilage architecture potentially through altering the crystallization and organization of cellulose.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Pentosiltransferases/metabolismo , Mucilagem Vegetal/metabolismo , Sementes/anatomia & histologia , Sementes/metabolismo , Xilanos/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Celulose/metabolismo , Cristalização , Regulação da Expressão Gênica de Plantas , Immunoblotting , Substâncias Macromoleculares/metabolismo , Mutação/genética , Pentosiltransferases/genética , Solubilidade , Espectroscopia de Infravermelho com Transformada de Fourier , Água , Xilose/metabolismo
18.
PLoS One ; 11(1): e0145092, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-26731606

RESUMO

Fundamental processes that underpin plant growth and development depend crucially on the action and assembly of the cell wall, a dynamic structure that changes in response to both developmental and environmental cues. While much is known about cell wall structure and biosynthesis, much less is known about the functions of the individual wall components, particularly with respect to their potential roles in cellular signaling. Loss-of-function mutants of two arabinogalactan-protein (AGP)-specific galactosyltransferases namely, GALT2 and GALT5, confer pleiotropic growth and development phenotypes indicating the important contributions of carbohydrate moieties towards AGP function. Notably, galt2galt5 double mutants displayed impaired root growth and root tip swelling in response to salt, likely as a result of decreased cellulose synthesis. These mutants phenocopy a salt-overly sensitive mutant called sos5, which lacks a fasciclin-like AGP (SOS5/FLA4) as well as a fei1fei2 double mutant, which lacks two cell wall-associated leucine-rich repeat receptor-like kinases. Additionally, galt2gal5 as well as sos5 and fei2 showed reduced seed mucilage adherence. Quintuple galt2galt5sos5fei1fei2 mutants were produced and provided evidence that these genes act in a single, linear genetic pathway. Further genetic and biochemical analysis of the quintuple mutant demonstrated involvement of these genes with the interplay between cellulose biosynthesis and two plant growth regulators, ethylene and ABA, in modulating root cell wall integrity.


Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Moléculas de Adesão Celular/genética , Raízes de Plantas/genética , Proteínas Serina-Treonina Quinases/genética , Receptores Proteína Tirosina Quinases/genética , Sementes/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Moléculas de Adesão Celular/metabolismo , Proliferação de Células/efeitos dos fármacos , Proliferação de Células/genética , Parede Celular/genética , Parede Celular/metabolismo , Celulose/biossíntese , Galactosiltransferases/genética , Galactosiltransferases/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Glicosilação , Lignina/metabolismo , Mutação , Reguladores de Crescimento de Planta/farmacologia , Mucilagem Vegetal/metabolismo , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Receptores Proteína Tirosina Quinases/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Sementes/metabolismo , Transdução de Sinais/genética , Cloreto de Sódio/farmacologia , Sacarose/farmacologia
19.
Protoplasma ; 253(5): 1365-72, 2016 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26454638

RESUMO

The aim of the paper is to determine what happens with plasmodesmata when mucilage is secreted into the periplasmic space in plant cells. Ultrastructural analysis of the periendothelial zone mucilage cells was performed on examples of the ovule tissues of several sexual and apomictic Taraxacum species. The cytoplasm of the periendothelial zone cells was dense, filled by numerous organelles and profiles of rough endoplasmic reticulum and active Golgi dictyosomes with vesicles that contained fibrillar material. At the beginning of the differentiation process of the periendothelial zone, the cells were connected by primary plasmodesmata. However, during the differentiation and the thickening of the cell walls (mucilage deposition), the plasmodesmata become elongated and associated with cytoplasmic bridges. The cytoplasmic bridges may connect the protoplast to the plasmodesmata through the mucilage layers in order to maintain cell-to-cell communication during the differentiation of the periendothelial zone cells.


Assuntos
Diferenciação Celular , Citoplasma/metabolismo , Mucilagem Vegetal/metabolismo , Plasmodesmos/ultraestrutura , Taraxacum/citologia , Taraxacum/ultraestrutura , Comunicação Celular , Parede Celular/metabolismo , Retículo Endoplasmático Rugoso/fisiologia , Complexo de Golgi/fisiologia , Periplasma/metabolismo
20.
Plant Physiol ; 169(4): 2481-95, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26482889

RESUMO

All cells of terrestrial plants are fortified by walls composed of crystalline cellulose microfibrils and a variety of matrix polymers. Xylans are the second most abundant type of polysaccharides on Earth. Previous studies of Arabidopsis (Arabidopsis thaliana) irregular xylem (irx) mutants, with collapsed xylem vessels and dwarfed stature, highlighted the importance of this cell wall component and revealed multiple players required for its synthesis. Nevertheless, xylan elongation and substitution are complex processes that remain poorly understood. Recently, seed coat epidermal cells were shown to provide an excellent system for deciphering hemicellulose production. Using a coexpression and sequence-based strategy, we predicted several MUCILAGE-RELATED (MUCI) genes that encode glycosyltransferases (GTs) involved in the production of xylan. We now show that MUCI21, a member of an uncharacterized clade of the GT61 family, and IRX14 (GT43 protein) are essential for the synthesis of highly branched xylan in seed coat epidermal cells. Our results reveal that xylan is the most abundant xylose-rich component in Arabidopsis seed mucilage and is required to maintain its architecture. Characterization of muci21 and irx14 single and double mutants indicates that MUCI21 is a Golgi-localized protein that likely facilitates the addition of xylose residues directly to the xylan backbone. These unique branches seem to be necessary for pectin attachment to the seed surface, while the xylan backbone maintains cellulose distribution. Evaluation of muci21 and irx14 alongside mutants that disrupt other wall components suggests that mucilage adherence is maintained by complex interactions between several polymers: cellulose, xylans, pectins, and glycoproteins.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Glicosiltransferases/metabolismo , Pentosiltransferases/metabolismo , Mucilagem Vegetal/metabolismo , Sementes/metabolismo , Xilanos/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Parede Celular/metabolismo , Celulose/metabolismo , Genes Reporter , Glicosiltransferases/genética , Microfibrilas/química , Microfibrilas/metabolismo , Mutação , Pectinas/metabolismo , Pentosiltransferases/genética , Filogenia , Mucilagem Vegetal/química , Polímeros/química , Polímeros/metabolismo , Polissacarídeos/metabolismo , Sementes/genética , Análise de Sequência de DNA , Xilanos/química , Xilema/genética , Xilema/metabolismo
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