The Experts below are selected from a list of 495 Experts worldwide ranked by ideXlab platform
William J Lucas - One of the best experts on this subject based on the ideXlab platform.
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overexpression of arabidopsis Plasmodesmata germin like proteins disrupts root growth and development
The Plant Cell, 2012Co-Authors: Byungkook Ham, Byungho Kang, Fanchang Zeng, William J LucasAbstract:In plants, a population of non-cell-autonomous proteins (NCAPs), including numerous transcription factors, move cell to cell through Plasmodesmata (PD). In many cases, the intercellular trafficking of these NCAPs is regulated by their interaction with specific PD components. To gain further insight into the functions of this NCAP pathway, coimmunoprecipitation experiments were performed on a tobacco (Nicotiana tabacum) Plasmodesmal-enriched cell wall protein preparation using as bait the NCAP, pumpkin (Cucurbita maxima) PHLOEM PROTEIN16 (Cm-PP16). A Cm-PP16 interaction partner, Nt-PlasmodesmaL GERMIN-LIKE PROTEIN1 (Nt-PDGLP1) was identified and shown to be a PD-located component. Arabidopsis thaliana putative orthologs, PDGLP1 and PDGLP2, were identified; expression studies indicated that, postgermination, these proteins were preferentially expressed in the root system. The PDGLP1 signal peptide was shown to function in localization to the PD by a novel mechanism involving the endoplasmic reticulum-Golgi secretory pathway. Overexpression of various tagged versions altered root meristem function, leading to reduced primary root but enhanced lateral root growth. This effect on root growth was corrected with an inability of these chimeric proteins to form stable PD-localized complexes. PDGLP1 and PDGLP2 appear to be involved in regulating primary root growth by controlling phloem-mediated allocation of resources between the primary and lateral root meristems.
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Plasmodesmata bridging the gap between neighboring plant cells
Trends in Cell Biology, 2009Co-Authors: William J Lucas, Byungkook Ham, Jae-yean KimAbstract:Land plants have developed highly sophisticated intercellular channels called Plasmodesmata (PD) that mediate the cell-to-cell trafficking of signaling molecules, including non-cell autonomous proteins (NCAPs) and RNAs. Until recently, the biological significance of this position-dependent intercellular signaling system was underestimated, as only a limited number of endogenous NCAPs had been discovered. However, identification of an ever-increasing population of NCAPs suggests that the PD communication pathway is involved in diverse biological processes, ranging from development to pathogen defense. The identification of components involved in Plasmodesmal structure and associated signaling molecules is now yielding novel insights into the evolution and function of PD in mediating the trafficking of non-cell-autonomous information macromolecules. Important future challenges are to build a detailed model for the Plasmodesmal supramolecular complex and to further elucidate the molecular and cellular aspects of this novel plant cell-to-cell communication pathway.
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Movement of Macromolecules in Plant Cells Through Plasmodesmata
Science's STKE : signal transduction knowledge environment, 2006Co-Authors: Richard A. Jorgensen, William J LucasAbstract:Plasmodesmata are intercellular organelles in plants that allow the passage of molecules between plant cells. Movement through Plasmodesmata may allow transcription factors expressed in one cell to move into adjacent cells, thereby regulating gene expression non-cell autonomously. The two animations illustrate (i) movement of a protein through an individual Plasmodesma and (ii) an experiment to detect the movement of the transcription factor through Plasmodesmata from the L1 layer of a plant meristem into the L2 and L3 layers. These two animations would be useful in teaching plant biology or plant development or a cell biology class discussing mechanisms of intercellular transport.
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a subclass of plant heat shock cognate 70 chaperones carries a motif that facilitates trafficking through Plasmodesmata
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Koh Aoki, Friedrich Kragler, Beatriz Xoconostlecazares, William J LucasAbstract:Plasmodesmata establish a pathway for the trafficking of non-cell-autonomously acting proteins and ribonucleoprotein complexes. Plasmodesmal enriched cell fractions and the contents of enucleate sieve elements, in the form of phloem sap, were used to isolate and characterize heat shock cognate 70 (Hsc70) chaperones associated with this cell-to-cell transport pathway. Three Cucurbita maxima Hsc70 chaperones were cloned and functional and sequence analysis led to the identification of a previously uncharacterized subclass of non-cell-autonomous chaperones. The highly conserved nature of the heat shock protein 70 (Hsp70) family, in conjunction with mutant analysis, permitted the characterization of a motif that allows these Hsc70 chaperones to engage the Plasmodesmal non-cell-autonomous translocation machinery. Proof of concept that this motif is necessary for Hsp70 gain-of-movement function was obtained through the engineering of a human Hsp70 that acquired the capacity to traffic through Plasmodesmata. These results are discussed in terms of the roles likely played by this subclass of Hsc70 chaperones in the trafficking of non-cell-autonomous proteins.
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rice phloem thioredoxin h has the capacity to mediate its own cell to cell transport through Plasmodesmata
Planta, 1998Co-Authors: Yutaka Ishiwatari, Toru Fujiwara, K C Mcfarland, Keisuke Nemoto, Hiroaki Hayashi, Mitsuo Chino, William J LucasAbstract:Rice (Oryza sativa L.) phloem sieve tubes contain RPP13-1, a thioredoxin h protein that moves around the plant via the translocation stream. Such phloem-mobile proteins are thought to be synthesized in the companion cells prior to being transferred, through Plasmodesmata, to the enucleate sieve-tube members. In this study, in-situ hybridization experiments confirmed that expression of RPP13-1 is restricted to companion cells within the mature phloem. To test the hypothesis that RPP13-1 enters the sieve tube, via Plasmodesmata, recombinant RPP13-1 was expressed in Escherichia coli, extracted, purified and fluorescently labeled with fluorescein isothiocyanate (FITC) for use in microinjection experiments into tobacco (Nicotiana tabacum L.) mesophyll cells. The FITC-RPP13-1 moved from the injected cell into surrounding cells, whereas the E. coli thioredoxin, an evolutionary homolog of RPP13-1, when similarly labeled and injected, failed to move in this same experimental system. In addition, co-injection of RPP13-1 and FITC-dextrans established that RPP13-1 can induce an increase in Plasmodesmal size exclusion limit to a value greater than 9.4 but less than 20 kDa. Nine mutant forms of RPP13-1 were constructed and tested for their capacity to move from cell to cell; two such mutants were found to be incapable of movement. Crystal-structure prediction studies were performed on wild-type and mutant RPP13-1 to identify the location of structural motifs required for protein trafficking through Plasmodesmata. These studies are discussed with respect to Plasmodesmal-mediated transport of macromolecules within the companion cell-sieve tube complex.
Vitaly Citovsky - One of the best experts on this subject based on the ideXlab platform.
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The Plasmodesmal Localization Signal of TMV MP Is Recognized by Plant Synaptotagmin SYTA
American Society for Microbiology, 2018Co-Authors: Cheng Yuan, Sondra G. Lazarowitz, Vitaly CitovskyAbstract:Plant viruses cross the barrier of the plant cell wall by moving through intercellular channels, termed Plasmodesmata, to invade their hosts. They accomplish this by encoding movement proteins (MPs), which act to alter Plasmodesmal gating. How MPs target to Plasmodesmata is not well understood. Our recent characterization of the first Plasmodesmal localization signal (PLS) identified in a viral MP, namely, the MP encoded by the Tobamovirus Tobacco mosaic virus (TMV), now provides the opportunity to identify host proteins that recognize this PLS and may be important for its Plasmodesmal targeting. One such candidate protein is Arabidopsis synaptotagmin A (SYTA), which is required to form endoplasmic reticulum (ER)-plasma membrane contact sites and regulates the MP-mediated trafficking of begomoviruses, tobamoviruses, and potyviruses. In particular, SYTA interacts with, and regulates the cell-to-cell transport of, both TMV MP and the MP encoded by the Tobamovirus Turnip vein clearing virus (TVCV). Using in planta bimolecular fluorescence complementation (BiFC) and yeast two-hybrid assays, we show here that the TMV PLS interacted with SYTA. This PLS sequence was both necessary and sufficient for interaction with SYTA, and the Plasmodesmal targeting activity of the TMV PLS was substantially reduced in an Arabidopsis syta knockdown line. Our findings show that SYTA is one host factor that can recognize the TMV PLS and suggest that this interaction may stabilize the association of TMV MP with Plasmodesmata.Plant viruses use their movement proteins (MPs) to move through host intercellular connections, Plasmodesmata. Perhaps one of the most intriguing, yet least studied, aspects of this transport is the MP signal sequences and their host recognition factors. Recently, we have described the Plasmodesmal localization signal (PLS) of the Tobacco mosaic virus (TMV) MP. Here, we identified the Arabidopsis synaptotagmin A (SYTA) as a host factor that recognizes TMV MP PLS and promotes its association with the Plasmodesmal membrane. The significance of these findings is two-fold: (i) we identified the TMV MP association with the cell membrane at Plasmodesmata as an important PLS-dependent step in Plasmodesmal targeting, and (ii) we identified the plant SYTA protein that specifically recognizes PLS as a host factor involved in this step
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Plasmodesmata-associated proteins: can we see the whole elephant?
Plant signaling & behavior, 2014Co-Authors: Shoko Ueki, Vitaly CitovskyAbstract:Encased in rigid cell walls, plant cells have evolved unique channel structures, Plasmodesma (Pd), to create a pathway for molecular exchange between adjacent cells. Pd are basically cytoplasmic channels through the cell wall, which are lined by plasma membrane, and contain a modified strand of ER that spans them. These structures provide cytoplasmic and membrane continuity between connected cells, and that continuity is utilized for short and long distance molecular trafficking. Pd sphincters, made from constricting the Pd openings by outer layers of callose, together with the ER strand that occludes the Pd lumen set the upper limit for the size of molecules that can freely diffuse through the cytoplasmic component of the Pd channel. This limit, called the size exclusion limit (SEL), is a major factor that restricts macromolecular transport through Pd.
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Tobacco mosaic virus: a pioneer of cell-to-cell movement.
Philosophical transactions of the Royal Society of London. Series B Biological sciences, 1999Co-Authors: Vitaly CitovskyAbstract:Cell–to–cell movement of tobacco mosaic virus (TMV) is used to illustrate macromolecular traffic through plant intercellular connections, the Plasmodesmata. This transport process is mediated by a specialized viral movement protein, P30. In the initially infected cell, P30 is produced by transcription of a subgenomic RNA derived from the invading virus. Presumably, P30 then associates with a certain proportion of the viral RNA molecules, sequestering them from replication and mediating their transport into neighbouring uninfected host cells. This nucleoprotein complex is targeted to Plasmodesmata, possibly via interaction with the host cell cytoskeleton. Prior to passage through a Plasmodesma, the Plasmodesmal channel is dilated by the movement protein. It is proposed that targeting of P30–TMV RNA complexes to Plasmodesmata involves binding to a specific cell wall–associated receptor molecule. In addition, a cell wall–associated protein kinase, phosphorylates P30 at its carboxy–terminus and minimizes P30–induced interference with Plasmodesmatal permeability during viral infection.
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transport of proteins and nucleic acids through Plasmodesmata
Annual review of plant physiology and plant molecular biology, 1997Co-Authors: Soumitra Ghoshroy, Robert T Lartey, Jinsong Sheng, Vitaly CitovskyAbstract:▪ Abstract Despite a potentially key role in cell-to-cell communication, plant intercellular connections—the Plasmodesmata—have long been a biological “black box.” Little is known about their protein composition, regulatory mechanisms, or transport pathways. However, recent studies have shed some light on Plasmodesmal function. These connections have been shown to actively traffic proteins and protein–nucleic acid complexes between plant cells. This review describes these transport processes—specifically, cell-to-cell movement of plant viruses as well as endogenous cellular proteins—and discusses their possible mechanism(s). For comparison and to provide a broader perspective on the Plasmodesmal transport process, the current model for nuclear import, the only other known example of transport of large proteins and protein–nucleic acid complexes through a membrane pore, is summarized. Finally, the function of Plasmodesmata as communication boundaries within plant tissue is discussed.
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Transport of protein—nucleic acid complexes within and between plant cells
Membrane Protein Transport, 1995Co-Authors: Vitaly Citovsky, Patricia ZambryskiAbstract:Publisher Summary In eukaryotic organisms, nucleic acid molecules are constantly transported between the nucleus and the cytoplasm. This transport includes nuclear export and import of RNAs and nuclear import of retrotransposable elements and invading viruses. Higher plants have an additional nucleic acid transport system that allows infectious viral genomes to be transported between adjacent host cells. Nuclear import and Plasmodesmal transport of nucleic acids in plants exhibit several structural and functional similarities. This chapter focuses on two processes of nucleic acid transport in plants: (1) the transport of Agrobacterium single-stranded (ss) DNA through nuclear pores and (2) the movement of tobacco mosaic virus (TMV) genomic RNA through plant intercellular connections, the Plasmodesmata. Both processes involve single-stranded nucleic acids that are transported as complexes with specialized transport proteins. These proteins bind ssDNA and RNA, producing thin unfolded filaments of protein–nucleic acid transport complexes. In addition to shaping nucleic acid molecules in a transferable form, the transport proteins also provide specific signals for targeting and interaction with the nuclear pores or Plasmodesmal channels.
Andy Maule - One of the best experts on this subject based on the ideXlab platform.
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Opportunities and successes in the search for Plasmodesmal proteins
Protoplasma, 2011Co-Authors: Christine Faulkner, Andy MauleAbstract:The proteinaceous composition of Plasmodesmata (PDs) is a puzzle for which pieces have proven particularly difficult to find. This review describes the numerous approaches that have been undertaken in the search for PD-associated proteins and what each has contributed to our understanding of PD structure and function. These approaches include immunolocalisation of known proteins, proteomic characterisation of PD-enriched tissue fractions, high-throughput screens of random cDNAs and mutant screens. In addition to components of the cytoskeleton, novel proteins with predicted or unknown functions have been identified. Many of these have properties that relate to the symplastic and/or apoplastic faces of the plasma membrane. Mutant screens have identified proteins involved in previously unconnected cell pathways such as ROS signalling, implicating ROS in PD formation and regulation. Proteins associated with callose synthesis and degradation have also been identified and characterised, providing considerable weight to the hypothesis that callose deposition around the neck of the PD pore is one mechanism by which the PD aperture is regulated. The techniques described in this review have been developed such that it is to be expected that a considerable number of new PD proteins will be identified in coming years to fill in further detail of the structure and functional mechanisms of these dynamic pores.
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control of arabidopsis meristem development by thioredoxin dependent regulation of intercellular transport
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Yoselin Benitezalfonso, Carole L Thomas, Andy Maule, Michelle Cilia, Adrianna San K Roman, Stephen Hearn, David JacksonAbstract:Cell-to-cell transport in plants occurs through cytoplasmic channels called “Plasmodesmata” and is regulated by developmental and environmental factors. Callose deposition modulates Plasmodesmal transport in vivo, but little is known about the mechanisms that regulate this process. Here we report a genetic approach to identify mutants affecting Plasmodesmal transport. We isolated 5 mutants, named gfp arrested trafficking (gat), affected in GFP unloading from the phloem into the meristem. gat1 mutants were seedling lethal and carried lesions in an m-type thioredoxin that is expressed in non-green plastids of meristems and organ primordia. Callose and hydrogen peroxide accumulated in gat1 mutants, and WT plants subjected to oxidative conditions phenocopied the gat1 trafficking defects. Ectopic expression of GAT1 in mature leaves increased Plasmodesmal permeability and led to a delay in senescence and flowering time. We propose a role for the GAT1 thioredoxin in the redox regulation of callose deposition and symplastic permeability that is essential for meristem maintenance in Arabidopsis.
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Plasmodesmata 2004. Surfing the Symplasm
Plant physiology, 2005Co-Authors: Christine Faulkner, Andy Maule, Jeri Brandom, Karl J. OparkaAbstract:Communication between cells is necessary to coordinate plant development and physiology, and is modulated in response to environmental signals and pathogen attack. Plasmodesmata (PDs; singular Plasmodesma), plasma membrane-lined channels that cross the cell wall, are key components of this
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Ultrastructural and Temporal Observations of the Potyvirus Cylindrical Inclusions (CIs) Show That the CI Protein Acts Transiently in Aiding Virus Movement
Virology, 1998Co-Authors: I. M. Roberts, Daowen Wang, Kim Findlay, Andy MauleAbstract:A systematic ultrastructural study across the edge of an advancing infection in pea seed-borne mosaic potyvirus-infected pea cotyledons showed the cylindrical inclusion (CI) protein to exist in transient functional states. Initially, the characteristic CI pinwheel inclusion bodies were positioned centrally over the Plasmodesmal apertures (including those of Plasmodesmata connected to the previously infected cell), in agreement with a proposed role in virus movement (Carrington et al., 1998, Plant J., 13, in press). The viral coat protein was associated with these structures and was seen within the modified Plasmodesma, most notably in a continuous channel that passed along the axis of the pinwheel and through the Plasmodesma. The CI protein was not detected within the Plasmodesmal cavities. Later in the infection (i.e., behind the zone of active virus replication) the CI was no longer associated with cell walls, or with coat protein, and showed signs of structural degeneration. In contrast, the coat protein remained within Plasmodesmal cavities. The role of the CI in assisting virus movement is not known but the presence of the CI was linked with an apparent transient reduction in callose in the vicinity of the Plasmodesmata.
Jung-youn Lee - One of the best experts on this subject based on the ideXlab platform.
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Sphingolipid biosynthesis modulates Plasmodesmal ultrastructure and phloem unloading
Nature Plants, 2019Co-Authors: Dawei Yan, Shri Yadav, Andrea Paterlini, William Nicolas, Ilya Belevich, Magali Grison, Anne Vaten, Leila Karami, Sedeer El-showk, Jung-youn LeeAbstract:During phloem unloading, multiple cell-to-cell transport events move organic substances to the root meristem. Although the primary unloading event from the sieve elements to the phloem pole pericycle has been characterized to some extent, little is known about post-sieve element unloading. Here, we report a novel gene, PHLOEM UNLOADING MODULATOR (PLM), in the absence of which Plasmodesmata-mediated symplastic transport through the phloem pole pericycle–endodermis interface is specifically enhanced. Increased unloading is attributable to a defect in the formation of the endoplasmic reticulum–plasma membrane tethers during Plasmodesmal morphogenesis, resulting in the majority of pores lacking a visible cytoplasmic sleeve. PLM encodes a putative enzyme required for the biosynthesis of sphingolipids with very-long-chain fatty acid. Taken together, our results indicate that post-sieve element unloading involves sphingolipid metabolism, which affects Plasmodesmal ultrastructure. They also raise the question of how and why Plasmodesmata with no cytoplasmic sleeve facilitate molecular trafficking.
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Arabidopsis callose synthases CalS1/8 regulate Plasmodesmal permeability during stress
Nature Plants, 2016Co-Authors: Weier Cui, Jung-youn LeeAbstract:In response to biotic or abiotic stress, plants can regulate cell–cell communication by modulating Plasmodesmal permeability. Here the authors show that callose synthases CalS1/8 are involved in this process. Plants need to cope with biotic and abiotic stress through well-coordinated cell-to-cell communication to survive as sedentary organisms. Environmental challenges such as wounding, low temperature, oxidative states and pathogen infection are known to affect the symplasmic molecular exchange between plant cells determined by Plasmodesmal permeability. However, the signalling pathways and mechanisms by which different environmental stressors affect Plasmodesmal permeability are not well understood. Here we show that regulating callose accumulation at Plasmodesmal channels is a common strategy to alter Plasmodesmal permeability under both pathogen infection and mechanical wounding stress. We have identified Arabidopsis callose synthase 1 ( CalS1 ) and CalS8 as key genes involved in this process, and have integrated these new players into both known and novel signalling pathways that control responses to biotic and abiotic stress. Our studies provide experimental data that indicate the presence of specialized pathways tuned to respond to particular stressors, and new insights into how plants regulate Plasmodesmata in response to environmental assaults.
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Plasmodesmata in integrated cell signalling insights from development and environmental signals and stresses
Journal of Experimental Botany, 2014Co-Authors: Ross Sager, Jung-youn LeeAbstract:To survive as sedentary organisms built of immobile cells, plants require an effective intercellular communication system, both locally between neighbouring cells within each tissue and systemically across distantly located organs. Such a system enables cells to coordinate their intracellular activities and produce concerted responses to internal and external stimuli. Plasmodesmata, membrane-lined intercellular channels, are essential for direct cell-to-cell communication involving exchange of diffusible factors, including signalling and information molecules. Recent advances corroborate that Plasmodesmata are not passive but rather highly dynamic channels, in that their density in the cell walls and gating activities are tightly linked to developmental and physiological processes. Moreover, it is becoming clear that specific hormonal signalling pathways play crucial roles in relaying primary cellular signals to Plasmodesmata. In this review, we examine a number of studies in which Plasmodesmal structure, occurrence, and/or permeability responses are found to be altered upon given cellular or environmental signals, and discuss common themes illustrating how Plasmodesmal regulation is integrated into specific cellular signalling pathways.
Aart J. E. Van Bel - One of the best experts on this subject based on the ideXlab platform.
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(Questions)n on phloem biology. 2. Mass flow, molecular hopping, distribution patterns and macromolecular signalling.
Plant science : an international journal of experimental plant biology, 2011Co-Authors: Aart J. E. Van Bel, Michael Knoblauch, Alexandra C. U. Furch, Jens B. Hafke, John W. PatrickAbstract:a b s t r a c t This review speculates on correlations between mass flow in sieve tubes and the distribution of photoas- similates and macromolecular signals. Since micro- (low-molecular compounds) and macromolecules are withdrawn from, and released into, the sieve-tube sap at various rates, distribution patterns of these compounds do not strictly obey mass-flow predictions. Due to serial release and retrieval trans- port steps executed by sieve tube plasma membranes, micromolecules are proposed to "hop" between sieve element/companion cell complexes and phloem parenchyma cells under source-limiting conditions (apoplasmic hopping). Under sink-limiting conditions, micromolecules escape from sieve tubes via pore- Plasmodesma units and are temporarily stored. It is speculated that macromolecules "hop" between sieve elements and companion cells using Plasmodesmal trafficking mechanisms (symplasmic hopping). We explore how differential tagging may influence distribution patterns of macromolecules and how their bidirectional movement could arise. Effects of exudation techniques on the macromolecular composition of sieve-tube sap are discussed.
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Plasmodesma 2001 On Safari through the Symplast
The Plant cell, 2002Co-Authors: Michelle Cilia, Laurence C. Cantrill, Aart J. E. Van BelAbstract:Plant cells need to communicate with each other to orchestrate lifelong development, to integrate physiological processes, and to coordinate pathogen defense responses. The transmission of intercellular signals is an important means of regulating all plant life processes, from fertilization to senescence. In this framework, Plasmodesmata (PD)— nanopores lined by plasma membrane that bridge the cytoplasm of most plant cells to their neighbors—play a pivotal role. PD function as relay stations in a unique cellular internet for the rapid exchange of water, metabolites, and even macromolecules. Exciting progress has been made in the field of Plasmodesmal research, as reported at the 4th International Plasmodesma meeting in Cape Town, South Africa, in August 2001.
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ultrastructure of minor vein phloem and assimilate export in summer and winter leaves of the symplasmically loading evergreens ajuga reptans l aucuba japonica thunb and hedera helix l
Planta, 2001Co-Authors: Gudrun Hoffmannthoma, Aart J. E. Van Bel, Katrin EhlersAbstract:Minor-vein ultrastructure and sugar export were studied in mature summer and winter leaves of the three broadleaf-evergreen species Ajuga reptans var. artropurpurescens L., Aucuba japonica Thunb. and Hedera helix L. to assess temperature effects on phloem loading. Leaves of the perennial herb Ajuga exported substantial amounts of assimilates in form of raffinose-family oligosaccharides (RFOs). Its minor-vein companion cells represent typical intermediary cells (ICs), with numerous small vacuoles and abundant Plasmodesmal connectivity to the bundle sheath. The woody plants Hedera and Aucuba translocated sucrose as the dominant sugar species, and only traces of RFOs. Their minor-vein phloem possessed a layer of highly vacuolated cells (VCs) intervening between mesophyll and sieve elements. Depending on their location and ontogeny, VCs were classified either as companion or parenchyma cells. Both cell types showed symplasmic continuity to the adjacent mesophyll tissue although at a lower Plasmodesmal frequency compared to the Ajuga ICs. p-Chloromercuribenzenesulfonic acid did not reduce leaf sugar export in any of the plants, indicating a symplasmic mode of phloem loading. Winter leaves did not show symptoms of frost injury, and the vacuolar pattern in ICs and VCs was equally prominent in both seasons. Starch accumulation as a result of reduced phloem loading was not observed to be triggered by low temperature. In contrast, high amounts of starch were found in mesophyll and bundle-sheath cells of summer leaves. Physiological data on season-dependent leaf exudation showed the maintenance of sugar export in cold-acclimated winter leaves.
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Symplasmic connections between sieve element and companion cell in the stem phloem of Vicia faba L. have a molecular exclusion limit of at least 10 kDa
Planta, 1997Co-Authors: Ronald Kempers, Aart J. E. Van BelAbstract:High-molecular-weight fluorochromes were intracellularly injected into a sieve element of the fascicular stem phloem ofVicia faba L., using a modified membrane-potential-recording pressure probe. After stabilization of the membrane potential following microelectrode impalement, either LYCH (Lucifer Yellow CH), 4.4-kDa FITC-dextran (fluoresceinisothiocyanate-dextran) conjugate, or 3-kDa, 10-kDa or 40-kDa LYCH-dextran conjugate was microinjected into the sieve element. Longitudinal fluorochrome movement across the sieve plates and lateral displacement to the companion cells was detected with all the probes except the 40-kDa conjugate. This indicates that the molecular exclusion limit of the pore/Plasmodesma units between a sieve element and a companion cell in the fascicular stem phloem ofVicia faba lies between 10 kDa and 40 kDa.