The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
L. Andrew Staehelin - One of the best experts on this subject based on the ideXlab platform.
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Electron tomographic analysis of post-meiotic cytokinesis during pollen development in Arabidopsis thaliana
Planta, 2004Co-Authors: Marisa S. Otegui, L. Andrew StaehelinAbstract:The mechanism of Cell wall formation after male meiosis was studied in microsporocytes of Arabidopsis thaliana (L.) Heynh. by means of thin-section and immuno-electron microscopy and dual-axis electron tomography of high-pressure-frozen/freeze-substituted Cells. The Cellularization of four-nucleate microsporocytes involves a novel type of Cell Plate, called a post-meiotic-type Cell Plate. As in the syncytial endosperm, the microsporocyte Cell Plates assemble in association with mini-phragmoplasts. However, in contrast to the endosperm Cell Plates, post-meiotic type Cell Plates arise simultaneously across the entire division plane. Vesicles are transported along mini-phragmoplast microtubules by putative kinesin proteins and, prior to fusion, they become connected together by 24-nm-long linkers that resemble exocyst complexes. These vesicles fuse with each other to form wide tubules and wide tubular networks. In contrast to endosperm Cell Plates, the wide tubular networks in microsporocytes completely lack callose and do not appear to be constricted by dynamin rings. The most peripheral wide tubular networks begin to fuse with the plasma membrane before the more central Cell Plate assembly sites become integrated into a coherent Cell Plate. Fusion with the parental plasma membrane triggers callose synthesis and the wide tubular domains are converted into convoluted sheets. As the peripheral convoluted sheets accumulate callose and arabinogalactan proteins, they are converted into stub-like projections, which grow centripetally, i.e. toward the interior of the syncytium, fusing with the wide tubular networks already assembled in the division plane. We also demonstrate that the ribosome-excluding Cell Plate assembly matrix is delivered to the mini-phragmoplast with the first vesicles, and encompasses all the linked vesicles and intermediate stages in Cell Plate formation.
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Three-Dimensional Analysis of Syncytial-Type Cell Plates during Endosperm Cellularization Visualized by High Resolution Electron Tomography
The Plant Cell, 2001Co-Authors: Marisa S. Otegui, Sebastian Y. Bednarek, David N. Mastronarde, Byung-ho Kang, L. Andrew StaehelinAbstract:The three-dimensional architecture of syncytial-type Cell Plates in the endosperm of Arabidopsis has been analyzed at ∼6-nm resolution by means of dual-axis high-voltage electron tomography of high-pressure frozen/freeze-substituted samples. Mini-phragmoplasts consisting of microtubule clusters assemble between sister and nonsister nuclei. Most Golgi-derived vesicles appear connected to these microtubules by two molecules that resemble kinesin-like motor proteins. These vesicles fuse with each other to form hourglass-shaped intermediates, which become wide (∼45 nm in diameter) tubules, the building blocks of wide tubular networks. New mini-phragmoplasts also are generated de novo around the margins of expanding wide tubular networks, giving rise to new foci of Cell Plate growth, which later become integrated into the main Cell Plate. Spiral-shaped rings of the dynamin-like protein ADL1A constrict but do not fission the wide tubules at irregular intervals. These rings appear to maintain the tubular geometry of the network. The wide tubular network matures into a convoluted fenestrated sheet in a process that involves increases of 45 and 130% in relative membrane surface area and volume, respectively. The proportionally larger increase in volume appears to reflect callose synthesis. Upon fusion with the parental plasma membrane, the convoluted fenestrated sheet is transformed into a planar fenestrated sheet. This transformation involves clathrin-coated vesicles that reduce the relative membrane surface area and volume by ∼70%. A ribosome-excluding matrix encompasses the Cell Plate membranes from the fusion of the first vesicles until the onset of the planar fenestrated sheet formation. We postulate that this matrix contains the molecules that mediate Cell Plate assembly.
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Syncytial-type Cell Plates: a novel kind of Cell Plate involved in endosperm Cellularization of Arabidopsis.
The Plant Cell, 2000Co-Authors: Marisa S. Otegui, L. Andrew StaehelinAbstract:Cell wall formation in the syncytial endosperm of Arabidopsis was studied by using high-pressure-frozen/freeze-substituted developing seeds and immunocytochemical techniques. The endosperm Cellularization process begins at the late globular embryo stage with the synchronous organization of small clusters of oppositely oriented microtubules (∼10 microtubules in each set) into phragmoplast-like structures termed mini-phragmoplasts between both sister and nonsister nuclei. These mini-phragmoplasts produce a novel kind of Cell Plate, the syncytial-type Cell Plate, from Golgi-derived vesicles ∼63 nm in diameter, which fuse by way of hourglass-shaped intermediates into wide (∼45 nm in diameter) tubules. These wide tubules quickly become coated and surrounded by a ribosome-excluding matrix; as they grow, they branch and fuse with each other to form wide tubular networks. The mini-phragmoplasts formed between a given pair of nuclei produce aligned tubular networks that grow centrifugally until they merge into a coherent wide tubular network with the mini-phragmoplasts positioned along the network margins. The individual wide tubular networks expand laterally until they meet and eventually fuse with each other at the sites of the future Cell corners. Transformation of the wide tubular networks into noncoated, thin (∼27 nm in diameter) tubular networks begins at multiple sites and coincides with the appearance of clathrin-coated budding structures. After fusion with the syncytial Cell wall, the thin tubular networks are converted into fenestrated sheets and Cell walls. Immunolabeling experiments show that the Cell Plates and Cell walls of the endosperm differ from those of the embryo and maternal tissue in two features: their xyloglucans lack terminal fucose residues on the side chain, and callose persists in the Cell walls after the Cell Plates fuse with the parental plasma membrane. The lack of terminal fucose residues on xyloglucans suggests that these Cell wall matrix molecules serve both structural and storage functions.
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Caffeine inhibits Cell Plate formation by disrupting membrane reorganization just after the vesicle fusion step
Protoplasma, 1996Co-Authors: A. Lacey Samuels, L. Andrew StaehelinAbstract:We have re-examined the effects of caffeine on Cell Plate formation in synchronized tobacco BY-2 Cells by means of cryofixation, immunocytochemistry, and calcium staining techniques. Because cryofixation preserves structural intermediates of Cell Plates that are not seen in chemically fixed Cells, this methodology has enabled us to define not only when caffeine acts but also which assembly steps are inhibited. Caffeine acts at an early stage of cytokinesis, just after the Golgi-derived vesicles have arrived at the Cell equator and begun to fuse with each other via thin (20 nm) membrane tubules. This initial round of fusions produces a delicate membrane network which in control Cells is rapidly converted in a more substantial tubulo-vesicular network covered by a thick, fuzzy coat on its cytoplasmic surface. Caffeine disrupts the conversion of the fragile, thin, fusion tube-generated membrane network into the more stable tubulo-vesicular network, the assembly of its fuzzy coat, and the budding of clathrin-coated vesicles from its surface. Normally, the tubulo-vesicular network also provides the structural framework for calcium-dependent callose synthases that deposit a callose layer over the lumenal surface of the Cell Plate membranes. In the presence of caffeine, no stabilizing callose layer is formed, and the thin tubule membrane network fragments into vesicles of variable sizes. Cell Plates in caffeine-treated Cells stained with chlortetracycline, a fluorescent stain of membrane-associated calcium, also display a significant reduction in fluorescence at the Cell Plate, suggesting a major decrease in Cell Plate membrane-associated calcium. However, this latter finding needs to be confirmed by more sophisticated calcium measuring techniques. Current theories of the mechanism of action of caffeine, including its ability to disrupt local calcium gradients, are discussed within the new ultrastructural context that this study provides. Our findings, finally, suggest a new method for isolating just fused but not further matured Cell Plate forming vesicles for biochemical studies.
Marisa S. Otegui - One of the best experts on this subject based on the ideXlab platform.
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Electron tomographic analysis of post-meiotic cytokinesis during pollen development in Arabidopsis thaliana
Planta, 2004Co-Authors: Marisa S. Otegui, L. Andrew StaehelinAbstract:The mechanism of Cell wall formation after male meiosis was studied in microsporocytes of Arabidopsis thaliana (L.) Heynh. by means of thin-section and immuno-electron microscopy and dual-axis electron tomography of high-pressure-frozen/freeze-substituted Cells. The Cellularization of four-nucleate microsporocytes involves a novel type of Cell Plate, called a post-meiotic-type Cell Plate. As in the syncytial endosperm, the microsporocyte Cell Plates assemble in association with mini-phragmoplasts. However, in contrast to the endosperm Cell Plates, post-meiotic type Cell Plates arise simultaneously across the entire division plane. Vesicles are transported along mini-phragmoplast microtubules by putative kinesin proteins and, prior to fusion, they become connected together by 24-nm-long linkers that resemble exocyst complexes. These vesicles fuse with each other to form wide tubules and wide tubular networks. In contrast to endosperm Cell Plates, the wide tubular networks in microsporocytes completely lack callose and do not appear to be constricted by dynamin rings. The most peripheral wide tubular networks begin to fuse with the plasma membrane before the more central Cell Plate assembly sites become integrated into a coherent Cell Plate. Fusion with the parental plasma membrane triggers callose synthesis and the wide tubular domains are converted into convoluted sheets. As the peripheral convoluted sheets accumulate callose and arabinogalactan proteins, they are converted into stub-like projections, which grow centripetally, i.e. toward the interior of the syncytium, fusing with the wide tubular networks already assembled in the division plane. We also demonstrate that the ribosome-excluding Cell Plate assembly matrix is delivered to the mini-phragmoplast with the first vesicles, and encompasses all the linked vesicles and intermediate stages in Cell Plate formation.
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Three-Dimensional Analysis of Syncytial-Type Cell Plates during Endosperm Cellularization Visualized by High Resolution Electron Tomography
The Plant Cell, 2001Co-Authors: Marisa S. Otegui, Sebastian Y. Bednarek, David N. Mastronarde, Byung-ho Kang, L. Andrew StaehelinAbstract:The three-dimensional architecture of syncytial-type Cell Plates in the endosperm of Arabidopsis has been analyzed at ∼6-nm resolution by means of dual-axis high-voltage electron tomography of high-pressure frozen/freeze-substituted samples. Mini-phragmoplasts consisting of microtubule clusters assemble between sister and nonsister nuclei. Most Golgi-derived vesicles appear connected to these microtubules by two molecules that resemble kinesin-like motor proteins. These vesicles fuse with each other to form hourglass-shaped intermediates, which become wide (∼45 nm in diameter) tubules, the building blocks of wide tubular networks. New mini-phragmoplasts also are generated de novo around the margins of expanding wide tubular networks, giving rise to new foci of Cell Plate growth, which later become integrated into the main Cell Plate. Spiral-shaped rings of the dynamin-like protein ADL1A constrict but do not fission the wide tubules at irregular intervals. These rings appear to maintain the tubular geometry of the network. The wide tubular network matures into a convoluted fenestrated sheet in a process that involves increases of 45 and 130% in relative membrane surface area and volume, respectively. The proportionally larger increase in volume appears to reflect callose synthesis. Upon fusion with the parental plasma membrane, the convoluted fenestrated sheet is transformed into a planar fenestrated sheet. This transformation involves clathrin-coated vesicles that reduce the relative membrane surface area and volume by ∼70%. A ribosome-excluding matrix encompasses the Cell Plate membranes from the fusion of the first vesicles until the onset of the planar fenestrated sheet formation. We postulate that this matrix contains the molecules that mediate Cell Plate assembly.
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Syncytial-type Cell Plates: a novel kind of Cell Plate involved in endosperm Cellularization of Arabidopsis.
The Plant Cell, 2000Co-Authors: Marisa S. Otegui, L. Andrew StaehelinAbstract:Cell wall formation in the syncytial endosperm of Arabidopsis was studied by using high-pressure-frozen/freeze-substituted developing seeds and immunocytochemical techniques. The endosperm Cellularization process begins at the late globular embryo stage with the synchronous organization of small clusters of oppositely oriented microtubules (∼10 microtubules in each set) into phragmoplast-like structures termed mini-phragmoplasts between both sister and nonsister nuclei. These mini-phragmoplasts produce a novel kind of Cell Plate, the syncytial-type Cell Plate, from Golgi-derived vesicles ∼63 nm in diameter, which fuse by way of hourglass-shaped intermediates into wide (∼45 nm in diameter) tubules. These wide tubules quickly become coated and surrounded by a ribosome-excluding matrix; as they grow, they branch and fuse with each other to form wide tubular networks. The mini-phragmoplasts formed between a given pair of nuclei produce aligned tubular networks that grow centrifugally until they merge into a coherent wide tubular network with the mini-phragmoplasts positioned along the network margins. The individual wide tubular networks expand laterally until they meet and eventually fuse with each other at the sites of the future Cell corners. Transformation of the wide tubular networks into noncoated, thin (∼27 nm in diameter) tubular networks begins at multiple sites and coincides with the appearance of clathrin-coated budding structures. After fusion with the syncytial Cell wall, the thin tubular networks are converted into fenestrated sheets and Cell walls. Immunolabeling experiments show that the Cell Plates and Cell walls of the endosperm differ from those of the embryo and maternal tissue in two features: their xyloglucans lack terminal fucose residues on the side chain, and callose persists in the Cell walls after the Cell Plates fuse with the parental plasma membrane. The lack of terminal fucose residues on xyloglucans suggests that these Cell wall matrix molecules serve both structural and storage functions.
H. Ozaki - One of the best experts on this subject based on the ideXlab platform.
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Cell-Plate-line/bit-line complementary sensing (CBCS) architecture for ultra low-power DRAMs
IEEE Journal of Solid-State Circuits, 1996Co-Authors: T. Hamamoto, Y. Morooka, M. Asakura, H. OzakiAbstract:In the realization of gigabit scale DRAMs, one of the most serious problems is how to reduce the array power consumption without degradation of the operating margin and other characteristics. This paper proposes a new array architecture called Cell-Plate-line/bit-line complementary sensing (CBCS) architecture which realizes drastic array power reduction for both read/write operations and refresh operations, and develops a large readout voltage difference on the bit-line and Cell-Plate-line. For read/write operations, the array power reduces to only 0.2%, and for refresh operations becomes 36%, This architecture requires no unique process technology and no additional chip area. Using a test device with a 64-Mb DRAM process, the basic operation has been successfully demonstrated. This new memory core design realizes a high-density DRAM suitable for the 1-Gb level and beyond with power consumption significantly reduced.
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Cell-Plate-line and bit-line complementarily sensed (CBCS) architecture for ultra low-power non-destructive DRAMs
Digest of Technical Papers. Symposium on VLSI Circuits., 1995Co-Authors: T. Hamamoto, Y. Morooka, M. Asakura, H. OzakiAbstract:In order to develop very high density DRAMs, the reduction of memory-array current, accounting for over 80% of total chip current, must be given serious consideration. As the number of activated sense-amplifiers (SAs) increase, the amount of consumed charge on bit-lines (BLs) increases accordingly. This paper describes a novel circuit design, called Cell-Plate-Line and Bit-Line Complementarily Sensed (CBCS) Architecture. Only the selected SA of a whole array is activated, thereby reducing array read/write current to below 1% compared with conventional ones. Furthermore, refresh operation can easily be executed and the array refresh current is reduced to below 50% without loss of the read-out differential signal.
S. Saito - One of the best experts on this subject based on the ideXlab platform.
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a 60 ns 1 mb nonvolatile ferroelectric memory with a nondriven Cell Plate line write read scheme
International Solid-State Circuits Conference, 1996Co-Authors: H. Koike, T. Otsuki, T. Kimura, M. Fukuma, Y. Hayashi, Y. Maejima, N. Tanabe, K. Amantuma, T. Masuki, S. SaitoAbstract:This paper proposes three circuit technologies for achieving mega-bit-class nonvolatile ferroelectric RAMs (NVFRAMs). The proposed nondriven Cell Plate line write/read scheme (NDP scheme) accomplishes fast write/read operation equivalent to that of DRAMs. Problems and countermeasures in introducing this scheme into NVFRAMs are also discussed. A proposed optimized C/sub B//C/sub S/ Cell array design method provides a relationship between bit line capacitance C/sub B/ and memory Cell capacitance C/sub S/, which must be satisfied for read operations. Also reported is a reference voltage generator circuit that uses a dummy memory Cell. This circuit can generate an accurate reference voltage despite the variety of capacitors with differing characteristics that are contained in the NVFRAM. A 1-Mb NVFRAM prototype featuring the above technologies has been fabricated, using a 1.0-/spl mu/m CMOS process. This chip has an access time of 60 ns and a die size of 15.7/spl times/5.79 mm/sup 2/.
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A 60 ns 1 Mb nonvolatile ferroelectric memory with non-driven Cell Plate line write/read scheme
1996 IEEE International Solid-State Circuits Conference. Digest of TEchnical Papers ISSCC, 1996Co-Authors: H. Koike, T. Otsuki, T. Kimura, M. Fukuma, Y. Hayashi, Y. Maejima, K. Amanuma, N. Tanabe, T. Matsuki, S. SaitoAbstract:With increase in the capacity of nonvolatile memories, the range of their use has been widening. A nonvolatile ferroelectric RAM (NVFRAM) based on a 1-transistor and 1-capacitor (1T/1C) memory Cell has potential for fast-access time and small-chip size comparable with a DRAM. However, previously reported NVFRAMs are still slower than ordinary DRAMs, since driving a Cell-Plate line in NVFRAMs is slow. To avoid this, a non-driven Cell Plate line write/read scheme (NDP scheme) is presented which leads to NVFRAMs with as fast access time as DRAMs.
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A 60-ns 1-Mb nonvolatile ferroelectric memory with a nondriven Cell Plate line write/read scheme
IEEE Journal of Solid-State Circuits, 1996Co-Authors: H. Koike, T. Otsuki, T. Kimura, M. Fukuma, Y. Hayashi, Y. Maejima, N. Tanabe, K. Amantuma, T. Masuki, S. SaitoAbstract:This paper proposes three circuit technologies for achieving mega-bit-class nonvolatile ferroelectric RAMs (NVFRAMs). The proposed nondriven Cell Plate line write/read scheme (NDP scheme) accomplishes fast write/read operation equivalent to that of DRAMs. Problems and countermeasures in introducing this scheme into NVFRAMs are also discussed. A proposed optimized C/sub B//C/sub S/ Cell array design method provides a relationship between bit line capacitance C/sub B/ and memory Cell capacitance C/sub S/, which must be satisfied for read operations. Also reported is a reference voltage generator circuit that uses a dummy memory Cell. This circuit can generate an accurate reference voltage despite the variety of capacitors with differing characteristics that are contained in the NVFRAM. A 1-Mb NVFRAM prototype featuring the above technologies has been fabricated, using a 1.0-/spl mu/m CMOS process. This chip has an access time of 60 ns and a die size of 15.7/spl times/5.79 mm/sup 2/.
T. Hamamoto - One of the best experts on this subject based on the ideXlab platform.
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Cell-Plate-line/bit-line complementary sensing (CBCS) architecture for ultra low-power DRAMs
IEEE Journal of Solid-State Circuits, 1996Co-Authors: T. Hamamoto, Y. Morooka, M. Asakura, H. OzakiAbstract:In the realization of gigabit scale DRAMs, one of the most serious problems is how to reduce the array power consumption without degradation of the operating margin and other characteristics. This paper proposes a new array architecture called Cell-Plate-line/bit-line complementary sensing (CBCS) architecture which realizes drastic array power reduction for both read/write operations and refresh operations, and develops a large readout voltage difference on the bit-line and Cell-Plate-line. For read/write operations, the array power reduces to only 0.2%, and for refresh operations becomes 36%, This architecture requires no unique process technology and no additional chip area. Using a test device with a 64-Mb DRAM process, the basic operation has been successfully demonstrated. This new memory core design realizes a high-density DRAM suitable for the 1-Gb level and beyond with power consumption significantly reduced.
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Cell-Plate-line and bit-line complementarily sensed (CBCS) architecture for ultra low-power non-destructive DRAMs
Digest of Technical Papers. Symposium on VLSI Circuits., 1995Co-Authors: T. Hamamoto, Y. Morooka, M. Asakura, H. OzakiAbstract:In order to develop very high density DRAMs, the reduction of memory-array current, accounting for over 80% of total chip current, must be given serious consideration. As the number of activated sense-amplifiers (SAs) increase, the amount of consumed charge on bit-lines (BLs) increases accordingly. This paper describes a novel circuit design, called Cell-Plate-Line and Bit-Line Complementarily Sensed (CBCS) Architecture. Only the selected SA of a whole array is activated, thereby reducing array read/write current to below 1% compared with conventional ones. Furthermore, refresh operation can easily be executed and the array refresh current is reduced to below 50% without loss of the read-out differential signal.