The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Aart J. E. Van Bel - One of the best experts on this subject based on the ideXlab platform.
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Sieve Elements: The Favourite Habitat of Phytoplasmas.
Methods in molecular biology (Clifton N.J.), 2018Co-Authors: Aart J. E. Van BelAbstract:The sieve elements are the only plant compartments, where phytoplasmas can survive and propagate. Therefore, this chapter is focussed on the specific molecular and Cell-biological properties of the sieve element. Sieve element-Companion Cell complexes arise from (pro)cambial mother Cells induced by key genes known to be decisive for sieve-element differentiation. The special anatomy, Cell biology, and plasma-membrane outfit of sieve elements allows them to act collectively as a tube system that is able to drive a mass flow against the flow induced by transpiration. Plasmodesmal corridors are vital for the translocation of photoassimilates and systemic signals and for survival of the enucleate sieve elements. Of paramount importance is the Ca2+-dependent gating of plasmodesmata by callose and proteins. Hence, some of the complex, regulatory mechanisms to maintain Ca2+ homoeostasis in sieve elements are presented. Finally, the peculiarities of the chemical and physical sieve-element environment offered to phytoplasmas are discussed.
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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 Since micro- (low-molecular compounds) and macromolecules are withdrawn from, and released into, the sieve-tube sap at various rates, distribution patterns of these compounds do not strictly obey mass-flow predictions.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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Physiochemical Determinants of Phloem Transport
Vascular Transport in Plants, 2005Co-Authors: Aart J. E. Van Bel, Jens B. HafkeAbstract:Publisher Summary This chapter identifies several questions as to the physiochemical determinants of phloem transport. There is a general quantitative unawareness with regard to physiochemical parameters. Moreover, one must be thoughtful of potentially large differences between plant species due to disparate structural/functional conditions. The steepness of the hydraulic gradient depends on the physiological activities along the whole sieve tube stretch. Thus, diversity in modes of phloem loading, release/retrieval along the transport pathway, and in modes of phloem unloading, may have a strong impact on generation of the hydraulic pressure gradient. This recognition requires detailed studies on deployment and functioning of proteins involved in shuttling osmotic equivalents and water through the sieve element/Companion Cell (SE/CC) plasma membrane of the successive phloem zones and the structural frame of the SE/CCs in various plant groups. Furthermore, the reciprocal feedback regulation of sources and sinks and the compensatory and buffering activities of transport phloem must be investigated on the Cell-biological level.
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The Companion Cell-Specific Arabidopsis Disaccharide Carrier AtSUC2 Is Expressed in Nematode-Induced Syncytia
Plant physiology, 2003Co-Authors: Katja Juergensen, Aart J. E. Van Bel, Norbert Sauer, Joachim Scholz-starke, Paul H. Hess, Florian M. W. GrundlerAbstract:Cyst nematodes induce a metabolically highly active syncytial Cell complex in host roots. The syncytia are symplastically isolated. Because they form a strong sink, assimilates must be imported via the apoplast, thus suggesting that specific membrane-bound sugar transport proteins are expressed and activated. To identify possible candidate genes, transgenic Arabidopsis plants expressing different reporter genes under the control of different promoters from Arabidopsis sugar transporter genes were infected with the beet cyst nematode (Heterodera schachtii). With polymerase chain reaction, 13 additional sugar transporters were tested for their presence in the syncytia through the use of a syncytium-specific cDNA library. Analysis of the infected roots showed that the promoter of the sucrose (Suc) transporter AtSUC2 gene that codes for a Companion Cell-specific Suc transporter in noninfected plants was found to be expressed in syncytia. Its expression patterns in β-glucuronidase and green fluorescent protein plants were monitored. Syncytium-specific gene expression was confirmed by reverse transcriptase-polymerase chain reaction. Results support the idea that AtSUC2 mediates the transmembrane transfer of Suc. AtSUC2 is the first disaccharide carrier described to be activated by pathogens.
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Sieve elements caught in the act
Trends in Plant Science, 2002Co-Authors: Aart J. E. Van Bel, Katrin Ehlers, Michael KnoblauchAbstract:Phloem is a puzzling plant tissue owing to the unique natural defence responses of the sieve elements to any kind of mechanical manipulation. Recent non-invasive studies have enabled real-time observation of events in intact sieve tubes, including mass transport, sieve-pore sealing and conformational changes of structural proteins. These studies further highlighted the importance of the symplasmic setting for development and functioning of the sieve elements. Exchange of macromolecules between Companion Cells and sieve elements is indispensable for the survival of the sieve element, but also seems to be involved in long-distance communication. How the branched plasmodesmata between sieve element and Companion Cell function as corridors for the passage of macromolecules is an intriguing but unresolved story.
Ronald Kempers - One of the best experts on this subject based on the ideXlab platform.
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symplasmic constriction and ultrastructural features of the sieve element Companion Cell complex in the transport phloem of apoplasmically and symplasmically phloem loading species
Plant Physiology, 1998Co-Authors: Ronald Kempers, Ankie Ammerlaan, Aart J. E. Van BelAbstract:The ultrastructural features of the sieve element/Companion Cell complexes were screened in the stem phloem of two symplasmically loading (squash, [Cucurbita maxima L.] and Lythrum salicaria L.) and two apoplasmically loading (broad bean [Vicia faba L.] and Zinnia elegans L.) species. The distinct ultrastructural differences between the Companion Cells in the collection phloem of symplasmically and apoplasmically phloem-loading species continue to exist in the transport phloem. Plasmodesmograms of the stem phloem showed a universal symplasmic constriction at the interface between the sieve element/Companion Cell complex and the phloem parenchyma Cells. This contrasts with the huge variation in symplasmic continuity between Companion Cells and adjoining Cells in the collection phloem of symplasmically and apoplasmically loading species. Further, the ultrastructure of the Companion Cells in the transport phloem faintly reflected the features of the Companion Cells in the loading zone of the transport phloem. The Companion Cells of squash contained numerous small vacuoles (or vesicles), and those of L. salicaria contained a limited number of vacuoles. The Companion Cells of broad bean and Z. elegans possessed small wall protrusions. Implications of the present findings for carbohydrate processing in intact plants are discussed.
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Symplasmic Constriction and Ultrastructural Features of the Sieve Element/Companion Cell Complex in the Transport Phloem of Apoplasmically and Symplasmically Phloem-Loading Species
Plant Physiology, 1998Co-Authors: Ronald Kempers, Ankie Ammerlaan, Aart J. E. Van BelAbstract:The ultrastructural features of the sieve element/Companion Cell complexes were screened in the stem phloem of two symplasmically loading (squash, [Cucurbita maxima L.] and Lythrum salicaria L.) and two apoplasmically loading (broad bean [Vicia faba L.] and Zinnia elegans L.) species. The distinct ultrastructural differences between the Companion Cells in the collection phloem of symplasmically and apoplasmically phloem-loading species continue to exist in the transport phloem. Plasmodesmograms of the stem phloem showed a universal symplasmic constriction at the interface between the sieve element/Companion Cell complex and the phloem parenchyma Cells. This contrasts with the huge variation in symplasmic continuity between Companion Cells and adjoining Cells in the collection phloem of symplasmically and apoplasmically loading species. Further, the ultrastructure of the Companion Cells in the transport phloem faintly reflected the features of the Companion Cells in the loading zone of the transport phloem. The Companion Cells of squash contained numerous small vacuoles (or vesicles), and those of L. salicaria contained a limited number of vacuoles. The Companion Cells of broad bean and Z. elegans possessed small wall protrusions. Implications of the present findings for carbohydrate processing in intact plants are discussed.
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Symplasmic connections between sieve element and Companion Cell in the stem phloem ofVicia faba L. have a molecular exclusion limit of at least 10 kDa
Planta, 1997Co-Authors: Ronald Kempers, Aart J. E. BelAbstract:High-molecular-weight fluorochromes were intraCellularly injected into a sieve element of the fascicular stem phloem of Vicia 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 of Vicia faba lies between 10 kDa and 40 kDa.
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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.
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The Pore/Plasmodesm Unit; Key Element in the Interplay Between Sieve Element and Companion Cell
Progress in Botany, 1997Co-Authors: Aart J. E. Van Bel, Ronald KempersAbstract:The principal function of the phloem system is the long-distance transport and distribution of photosynthate. Hence, the phloem is vital for concerted growth and development of higher plants. The transport elements of the phloem are the sieve tubes, arrays of numerous units, each of which is composed of a sieve element and a Companion Cell (sieve element/Companion Cell complex or SE/CC).
Harold V.m. Van Rijen - One of the best experts on this subject based on the ideXlab platform.
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Microelectrode-recorded development of the symplasmic autonomy of the sieve element/Companion Cell complex in the stem phloem ofLupinus luteus L.
Planta, 1994Co-Authors: Aart J. E. Bel, Harold V.m. Van RijenAbstract:From the cambial stage onwards, the symplasmic autonomy of sieve element/Companion Cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma Cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intraCellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multiCellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.
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Microelectrode-recorded development of the symplasmic autonomy of the sieve element/Companion Cell complex in the stem phloem ofLupinus luteus L.
Planta, 1994Co-Authors: Aart J. E. Bel, Harold V.m. Van RijenAbstract:From the cambial stage onwards, the symplasmic autonomy of sieve element/Companion Cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma Cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intraCellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multiCellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.
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Microelectrode-recorded development of the symplasmic autonomy of the sieve element/Companion Cell complex in the stem phloem of Lupinus luteus L.
Planta, 1994Co-Authors: Aart J. E. Bel, Harold V.m. Van RijenAbstract:From the cambial stage onwards, the symplasmic autonomy of sieve element/Companion Cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma Cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intraCellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multiCellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.
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Microelectrode-recorded development of the symplasmic autonomy of the sieve element/Companion Cell complex in the stem phloem of Lupinus luteus L.
Planta, 1994Co-Authors: Aart J. E. Bel, Harold V.m. Van RijenAbstract:From the cambial stage onwards, the symplasmic autonomy of sieve element/Companion Cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma Cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intraCellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multiCellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.
Aart J. E. Bel - One of the best experts on this subject based on the ideXlab platform.
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Symplasmic connections between sieve element and Companion Cell in the stem phloem ofVicia faba L. have a molecular exclusion limit of at least 10 kDa
Planta, 1997Co-Authors: Ronald Kempers, Aart J. E. BelAbstract:High-molecular-weight fluorochromes were intraCellularly injected into a sieve element of the fascicular stem phloem of Vicia 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 of Vicia faba lies between 10 kDa and 40 kDa.
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Microelectrode-recorded development of the symplasmic autonomy of the sieve element/Companion Cell complex in the stem phloem ofLupinus luteus L.
Planta, 1994Co-Authors: Aart J. E. Bel, Harold V.m. Van RijenAbstract:From the cambial stage onwards, the symplasmic autonomy of sieve element/Companion Cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma Cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intraCellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multiCellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.
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Microelectrode-recorded development of the symplasmic autonomy of the sieve element/Companion Cell complex in the stem phloem ofLupinus luteus L.
Planta, 1994Co-Authors: Aart J. E. Bel, Harold V.m. Van RijenAbstract:From the cambial stage onwards, the symplasmic autonomy of sieve element/Companion Cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma Cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intraCellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multiCellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.
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Microelectrode-recorded development of the symplasmic autonomy of the sieve element/Companion Cell complex in the stem phloem of Lupinus luteus L.
Planta, 1994Co-Authors: Aart J. E. Bel, Harold V.m. Van RijenAbstract:From the cambial stage onwards, the symplasmic autonomy of sieve element/Companion Cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma Cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intraCellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multiCellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.
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Microelectrode-recorded development of the symplasmic autonomy of the sieve element/Companion Cell complex in the stem phloem of Lupinus luteus L.
Planta, 1994Co-Authors: Aart J. E. Bel, Harold V.m. Van RijenAbstract:From the cambial stage onwards, the symplasmic autonomy of sieve element/Companion Cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma Cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intraCellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multiCellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.
Da-peng Zhang - One of the best experts on this subject based on the ideXlab platform.
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a shift of phloem unloading from symplasmic to apoplasmic pathway is involved in developmental onset of ripening in grape berry
Plant Physiology, 2006Co-Authors: Xiaoyan Zhang, Xiuling Wang, Xiaofang Wang, Guohai Xia, Qiuhong Pan, Renchun Fan, Da-peng ZhangAbstract:It remains unclear whether the phloem unloading pathway alters to adapt to developmental transition in fleshy fruits that accumulate high level of soluble sugars. Using a combination of electron microscopy, transport of the phloem-mobile symplasmic tracer carboxyfluorescein, movement of the Companion Cell-expressed and the green fluorescent protein-tagged viral movement protein, and assays of the sucrose cleavage enzymes, the pathway of phloem unloading was studied in the berries of a hybrid grape (Vitis vinifera x Vitis labrusca). Structural investigations showed that the sieve element-Companion Cell complex is apparently symplasmically connected through plasmodesmata with surrounding parenchyma Cells throughout fruit development, though a small portion of plasmodesmata are apparently blocked in the ripening stage. Both carboxyfluorescein and the green fluorescent protein-tagged viral movement protein were released from the functional phloem strands during the early and middle stages of fruit development, whereas the two symplasmic tracers were confined to the phloem strands during the late stage. This reveals a shift of phloem unloading from symplasmic to apoplasmic pathway during fruit development. The turning point of the phloem unloading pathways was further shown to be at or just before onset of ripening, an important developmental checkpoint of grape berry. In addition, the levels of both the expression and activities of Cell wall acid invertase increased around the onset of ripening and reached a high level in the late stage, providing further evidence for an operation of the apoplasmic unloading pathway after onset of ripening. These data demonstrate clearly the occurrence of an adaptive shift of phloem unloading pathway to developmental transition from growing phase to ripening in grape berry.
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Evidence for Apoplasmic Phloem Unloading in Developing Apple Fruit
Plant Physiology, 2004Co-Authors: Ling-yun Zhang, Yi-ben Peng, Sandrine Pelleschi-travier, Ying Fan, Yan-fen Lu, Ying-min Lu, Xiu-ping Gao, Yuan-yue Shen, Serge Delrot, Da-peng ZhangAbstract:The phloem unloading pathway remains unclear in fleshy fruits accumulating a high level of soluble sugars. A structural investigation in apple fruit (Malus domestica Borkh. cv Golden Delicious) showed that the sieve element-Companion Cell complex of the sepal bundles feeding the fruit flesh is symplasmically isolated over fruit development. 14C-autoradiography indicated that the phloem of the sepal bundles was functional for unloading. Confocal laser scanning microscopy imaging of carboxyfluorescein unloading showed that the dye remained confined to the phloem strands of the sepal bundles from the basal to the apical region of the fruit. A 52-kD putative monosaccharide transporter was immunolocalized predominantly in the plasma membrane of both the sieve elements and parenchyma Cells and its amount increased during fruit development. A 90-kD plasma membrane H1-ATPase was also localized in the plasma membrane of the sieve element-Companion Cell complex. Studies of [14C]sorbitol unloading suggested that an energy-driven monosaccharide transporter may be functional in phloem unloading. These data provide clear evidence for an apoplasmic phloem unloading pathway in apple fruit and give information on the structural and molecular features involved in this process.
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Acid invertase is predominantly localized to Cell walls of both the practically symplasmically isolated sieve element/Companion Cell complex and parenchyma Cells in developing apple fruits
Plant Cell & Environment, 2001Co-Authors: Da-peng Zhang, Yanping Wang, Chaorui Duan, H. Y. YanAbstract:The acid invertase (β-fructosidase, EC 3·2·1·26) was localized at subCellular level via immunogold electron microscopy in the phloem-unloading zone of developing apple fruit. The enzyme (immunogold particles) was found to reside predominantly in the Cell walls of the sieve element/Companion Cell (SE/CC) complex, phloem parenchyma Cells and other parenchyma Cells. There was almost no gold particle found in cytoplasm and vacuole. This distribution pattern remained unchanged throughout the growing season, but the enzyme numbers varied. The density of immunogold particles increased during fruit development. The immunoblotting of soluble and insoluble acid invertases provided a supporting proof for the assays of immunolocalization. The biochemical analysis showed a predominantly Cell-wall-distributed activity of acid invertase that corresponds essentially with its amount distribution. The ultrastructural observations showed that there were numerous plasmodesmata between the parenchyma Cells, but almost no plasmodesmium between the SE/CC complex and its surrounding parenchyma Cells, practically resulting in the symplasmic isolation of the SE/CC complex. It is therefore suggested that the unloading pathway of sucrose from the SE/CC complex may be predominantly apoplasmic in the developing apple fruit, and that the unloaded sucrose may be hydrolysed by the functional acid invertase localized in the Cell wall before it is loaded in sink Cells.
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acid invertase is predominantly localized to Cell walls of both the practically symplasmically isolated sieve element Companion Cell complex and parenchyma Cells in developing apple fruits
Plant Cell and Environment, 2001Co-Authors: Da-peng Zhang, Yanping Wang, Chaorui Duan, H. Y. YanAbstract:The acid invertase (β-fructosidase, EC 3·2·1·26) was localized at subCellular level via immunogold electron microscopy in the phloem-unloading zone of developing apple fruit. The enzyme (immunogold particles) was found to reside predominantly in the Cell walls of the sieve element/Companion Cell (SE/CC) complex, phloem parenchyma Cells and other parenchyma Cells. There was almost no gold particle found in cytoplasm and vacuole. This distribution pattern remained unchanged throughout the growing season, but the enzyme numbers varied. The density of immunogold particles increased during fruit development. The immunoblotting of soluble and insoluble acid invertases provided a supporting proof for the assays of immunolocalization. The biochemical analysis showed a predominantly Cell-wall-distributed activity of acid invertase that corresponds essentially with its amount distribution. The ultrastructural observations showed that there were numerous plasmodesmata between the parenchyma Cells, but almost no plasmodesmium between the SE/CC complex and its surrounding parenchyma Cells, practically resulting in the symplasmic isolation of the SE/CC complex. It is therefore suggested that the unloading pathway of sucrose from the SE/CC complex may be predominantly apoplasmic in the developing apple fruit, and that the unloaded sucrose may be hydrolysed by the functional acid invertase localized in the Cell wall before it is loaded in sink Cells.