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Emons AMC, Wolters-Arts AMC, Traas JA, Derksen J. The effect of colchicine on microtubules and microfibrils in root hairs. ACTA ACUST UNITED AC 2015. [DOI: 10.1111/j.1438-8677.1990.tb01442.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- A. M. C. Emons
- Department of Experimental Botany; University of Nijmegen; Toernooiveld 6525 ED Nijmegen The Netherlands
| | - A. M. C. Wolters-Arts
- Department of Experimental Botany; University of Nijmegen; Toernooiveld 6525 ED Nijmegen The Netherlands
| | - J. A. Traas
- Department of Experimental Botany; University of Nijmegen; Toernooiveld 6525 ED Nijmegen The Netherlands
| | - J. Derksen
- Department of Experimental Botany; University of Nijmegen; Toernooiveld 6525 ED Nijmegen The Netherlands
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2
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Derksen J, Wilms FHA, Pierson ES. The plant cytoskeleton: its significance in plant development. ACTA ACUST UNITED AC 2015. [DOI: 10.1111/j.1438-8677.1990.tb01441.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- J. Derksen
- Department of Experimental Botany; University of Nijmegen; Toernooiveld NL-6525 ED Nijmegen The Netherlands
| | - F. H. A. Wilms
- Department of Experimental Botany; University of Nijmegen; Toernooiveld NL-6525 ED Nijmegen The Netherlands
| | - E. S. Pierson
- Department of Experimental Botany; University of Nijmegen; Toernooiveld NL-6525 ED Nijmegen The Netherlands
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3
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Emons AMC, Derksen J. MICROFIBRILS, MICROTUBULES AND MICROFILAMENTS OF THE TRICHOBLAST OF EQUISETUM HYEMALE. ACTA ACUST UNITED AC 2015. [DOI: 10.1111/j.1438-8677.1986.tb01293.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- A. M. C. Emons
- Department of Botany; University of Nijmegen; Toernooiveld 6525 ED Nijmegen The Netherlands
| | - J. Derksen
- Department of Botany; University of Nijmegen; Toernooiveld 6525 ED Nijmegen The Netherlands
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4
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Affiliation(s)
- A. M. C. Emons
- Department of Plant Cytology and Morphology; Wageningen Agricultural University; Arboretumlaan 4 6703 BD Wageningen The Netherlands
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5
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Wang W, Wang L, Chen C, Xiong G, Tan XY, Yang KZ, Wang ZC, Zhou Y, Ye D, Chen LQ. Arabidopsis CSLD1 and CSLD4 are required for cellulose deposition and normal growth of pollen tubes. JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:5161-77. [PMID: 21765162 PMCID: PMC3193019 DOI: 10.1093/jxb/err221] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Revised: 06/20/2011] [Accepted: 06/20/2011] [Indexed: 05/19/2023]
Abstract
The cell wall is important for pollen tube growth, but little is known about the molecular mechanism that controls cell wall deposition in pollen tubes. Here, the functional characterization of the pollen-expressed Arabidopsis cellulose synthase-like D genes CSLD1 and CSLD4 that are required for pollen tube growth is reported. Both CSLD1 and CSLD4 are highly expressed in mature pollen grains and pollen tubes. The CSLD1 and CSLD4 proteins are located in the Golgi apparatus and transported to the plasma membrane of the tip region of growing pollen tubes, where cellulose is actively synthesized. Mutations in CSLD1 and CSLD4 caused a significant reduction in cellulose deposition in the pollen tube wall and a remarkable disorganization of the pollen tube wall layers, which disrupted the genetic transmission of the male gametophyte. In csld1 and csld4 single mutants and in the csld1 csld4 double mutant, all the mutant pollen tubes exhibited similar phenotypes: the pollen tubes grew extremely abnormally both in vitro and in vivo, which indicates that CSLD1 and CSLD4 are not functionally redundant. Taken together, these results suggest that CSLD1 and CSLD4 play important roles in pollen tube growth, probably through participation in cellulose synthesis of the pollen tube wall.
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Affiliation(s)
- Wei Wang
- State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Li Wang
- State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Chen Chen
- State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Guangyan Xiong
- Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
| | - Xiao-Yun Tan
- State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Ke-Zhen Yang
- State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Zi-Chen Wang
- State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Yihua Zhou
- Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
| | - De Ye
- State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Li-Qun Chen
- State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China
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6
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Diotallevi F, Mulder BM, Grasman J. On the robustness of the geometrical model for cell wall deposition. Bull Math Biol 2009; 72:869-95. [PMID: 20041352 DOI: 10.1007/s11538-009-9472-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2008] [Accepted: 10/15/2009] [Indexed: 11/28/2022]
Abstract
All plant cells are provided with the necessary rigidity to withstand the turgor by an exterior cell wall. This wall is composed of long crystalline cellulose microfibrils embedded in a matrix of other polysaccharides. The cellulose microfibrils are deposited by mobile membrane bound protein complexes in remarkably ordered lamellar textures. The mechanism by which these ordered textures arise, however, is still under debate. The geometrical model for cell wall deposition proposed by Emons and Mulder (Proc. Natl. Acad. Sci. 95, 7215-7219, 1998) provides a detailed approach to the case of cell wall deposition in non-growing cells, where there is no evidence for the direct influence of other cellular components such as microtubules. The model successfully reproduces even the so-called helicoidal wall; the most intricate texture observed. However, a number of simplifying assumptions were made in the original calculations. The present work addresses the issue of the robustness of the model to relaxation of these assumptions, by considering whether the helicoidal solutions survive when three aspects of the model are varied. These are: (i) the shape of the insertion domain, (ii) the distribution of lifetimes of individual CSCs, and (iii) fluctuations and overcrowding. Although details of the solutions do change, we find that in all cases the overall character of the helicoidal solutions is preserved.
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Affiliation(s)
- F Diotallevi
- FOM Institute for Atomic and Molecular Physics (AMOLF), Kruislaan 407, 1098SJ Amsterdam, The Netherlands
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7
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Arabidopsis cortical microtubules position cellulose synthase delivery to the plasma membrane and interact with cellulose synthase trafficking compartments. Nat Cell Biol 2009; 11:797-806. [PMID: 19525940 DOI: 10.1038/ncb1886] [Citation(s) in RCA: 458] [Impact Index Per Article: 30.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2009] [Accepted: 05/20/2009] [Indexed: 01/10/2023]
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8
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Intracellular Organization: A Prerequisite for Root Hair Elongation and Cell Wall Deposition. PLANT CELL MONOGRAPHS 2009. [DOI: 10.1007/978-3-540-79405-9_4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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9
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Nielsen E. Plant Cell Wall Biogenesis During Tip Growth in Root Hair Cells. PLANT CELL MONOGRAPHS 2009. [DOI: 10.1007/978-3-540-79405-9_11] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Lindeboom J, Mulder BM, Vos JW, Ketelaar T, Emons AMC. Cellulose microfibril deposition: coordinated activity at the plant plasma membrane. J Microsc 2008; 231:192-200. [PMID: 18778417 DOI: 10.1111/j.1365-2818.2008.02035.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Plant cell wall production is a membrane-bound process. Cell walls are composed of cellulose microfibrils, embedded inside a matrix of other polysaccharides and glycoproteins. The cell wall matrix is extruded into the existing cell wall by exocytosis. This same process also inserts the cellulose synthase complexes into the plasma membrane. These complexes, the nanomachines that produce the cellulose microfibrils, move inside the plasma membrane leaving the cellulose microfibrils in their wake. Cellulose microfibril angle is an important determinant of cell development and of tissue properties and as such relevant for the industrial use of plant material. Here, we provide an integrated view of the events taking place in the not more than 100 nm deep area in and around the plasma membrane, correlating recent results provided by the distinct field of plant cell biology. We discuss the coordinated activities of exocytosis, endocytosis, and movement of cellulose synthase complexes while producing cellulose microfibrils and the link of these processes to the cortical microtubules.
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Affiliation(s)
- J Lindeboom
- Laboratory of Plant Cell Biology, Wageningen University, Arboretumlaan 4, 6703 BD, Wageningen, The Netherlands
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11
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Diotallevi F, Mulder B. The cellulose synthase complex: a polymerization driven supramolecular motor. Biophys J 2007; 92:2666-73. [PMID: 17237206 PMCID: PMC1831695 DOI: 10.1529/biophysj.106.099473] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We present a biophysical model for the propulsion of the cellulose synthase complex, the motile transmembrane protein complex responsible for the biosynthesis of cellulose microfibrils, the dominant architectural component of the cell walls of higher plants. Our model identifies the polymerization and the crystallization of the cellulose chains as the combined driving forces and elucidates the role of polymer flexibility and membrane elasticity as force transducers. The model is elaborated using both stochastic simulations and a simplified analytical treatment. On the basis of the model and approximate values for the relevant physical constants, we estimate the speed of the cellulose synthase complex to be in the range v(p) approximately 10(-9)-10(-8) m/s, consistent with the recently reported experimental value of 5.8 x 10(-9) m/s.
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Affiliation(s)
- Fabiana Diotallevi
- FOM Institute for Atomic and Molecular Physics AMOLF, 1098 SJ Amsterdam, The Netherlands
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12
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Baskin TI. On the alignment of cellulose microfibrils by cortical microtubules: a review and a model. PROTOPLASMA 2001; 215:150-71. [PMID: 11732054 DOI: 10.1007/bf01280311] [Citation(s) in RCA: 241] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The hypothesis that microtubules align microfibrils, termed the alignment hypothesis, states that there is a causal link between the orientation of cortical microtubules and the orientation of nascent microfibrils. I have assessed the generality of this hypothesis by reviewing what is known about the relation between microtubules and microfibrils in a wide group of examples: in algae of the family Characeae, Closterium acerosum, Oocystis solitaria, and certain genera of green coenocytes and in land plant tip-growing cells, xylem, diffusely growing cells, and protoplasts. The salient features about microfibril alignment to emerge are as follows. Cellulose microfibrils can be aligned by cortical microtubules, thus supporting the alignment hypothesis. Alignment of microfibrils can occur independently of microtubules, showing that an alternative to the alignment hypothesis must exist. Microfibril organization is often random, suggesting that self-assembly is insufficient. Microfibril organization differs on different faces of the same cell, suggesting that microfibrils are aligned locally, not with respect to the entire cell. Nascent microfibrils appear to associate tightly with the plasma membrane. To account for these observations, I present a model that posits alignment to be mediated through binding the nascent microfibril. The model, termed templated incorporation, postulates that the nascent microfibril is incorporated into the cell wall by binding to a scaffold that is oriented; further, the scaffold is built and oriented around either already incorporated microfibrils or plasma membrane proteins, or both. The role of cortical microtubules is to bind and orient components of the scaffold at the plasma membrane. In this way, spatial information to align the microfibrils may come from either the cell wall or the cell interior, and microfibril alignment with and without microtubules are subsets of a single mechanism.
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Affiliation(s)
- T I Baskin
- Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211, USA
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13
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Brett CT. Cellulose microfibrils in plants: biosynthesis, deposition, and integration into the cell wall. INTERNATIONAL REVIEW OF CYTOLOGY 2000; 199:161-99. [PMID: 10874579 DOI: 10.1016/s0074-7696(00)99004-1] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Cellulose occurs in all higher plants and some algae, fungi, bacteria, and animals. It forms microfibrils containing the crystalline allomorphs, cellulose I alpha and I beta. Cellulose molecules are 500-15,000 glucose units long. What controls molecular size is unknown. Microfibrils are elongated by particle rosettes in the plasma membrane (cellulose synthase complexes). The precursor, UDP-glucose, may be generated from sucrose at the site of synthesis. The biosynthetic mechanism may involve lipid-linked intermediates. Cellulose synthase has been purified from bacteria, but not from plants. In plants, disrupted cellulose synthase may form callose. Cellulose synthase genes have been isolated from bacteria and plants. Cellulose-deficient mutants have been characterised. The deduced amino acid sequence suggests possible catalytic mechanisms. It is not known whether synthesis occurs at the reducing or nonreducing end. Endoglucanase may play a role in synthesis. Nascent cellulose molecules associate by Van der Waals and hydrogen bonds to form microfibrils. Cortical microtubules control microfibril orientation, thus determining the direction of cell growth. Self-assembly mechanisms may operate. Microfibril integration into the wall occurs by interactions with matrix polymers during microfibril formation.
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Affiliation(s)
- C T Brett
- Plant Molecular Science Group, Institute of Biomedical and Life Sciences, University of Glasgow, United Kingdom
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Emons AM, Mulder BM. How the deposition of cellulose microfibrils builds cell wall architecture. TRENDS IN PLANT SCIENCE 2000; 5:35-40. [PMID: 10637660 DOI: 10.1016/s1360-1385(99)01507-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Cell walls, the extracytoplasmic matrices of plant cells, consist of an ordered array of cellulose microfibrils embedded in a matrix of polysaccharides and glycoproteins. This construction is reminiscent of steel rods in reinforced concrete. How a cell organizes these ordered textures around itself, creating its own desirable environment, is a fascinating question. We believe that nature adopted an economical solution to this design problem: it exploits the geometrical constraints imposed by the shape of the cell and the limited space in which microfibrils are deposited, enabling the wall textures essentially to 'build themselves'. This does not imply that the cell cannot control its wall texture. On the contrary, the cell has ample regulatory mechanisms to control wall texture formation by controlling the insertion of synthases and the distance between individual microfibrils within a wall lamella.
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Affiliation(s)
- A M Emons
- aLaboratory of Experimental Plant Morphology and Cell Biology, Dept of Plant Sciences, Wageningen University, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands.
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Ha MA, Apperley DC, Evans BW, Huxham IM, Jardine WG, Viëtor RJ, Reis D, Vian B, Jarvis MC. Fine structure in cellulose microfibrils: NMR evidence from onion and quince. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 1998; 16:183-90. [PMID: 22507135 DOI: 10.1046/j.1365-313x.1998.00291.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
It has been controversial for many years whether in the cellulose of higher plants, the microfibrils are aggregates of 'elementary fibrils', which have been suggested to be about 3.5 nm in diameter. Solid-state NMR spectroscopy was used to examine two celluloses whose fibril diameters had been established by electron microscopy: onion (8-10 nm, but containing 40% of xyloglucan as well as cellulose) and quince (2 nm cellulose core). Both of these forms of cellulose contained crystalline units of similar size, as estimated from the ratio of surface to interior chains, and the time required for proton magnetisation to diffuse from the surface to the interior. It is suggested that the onion microfibrils must therefore be constructed from a number of cellulose subunits 2 nm in diameter, smaller than the 'elementary fibrils' envisaged previously. The size of these subunits would permit a hexagonal arrangement resembling the cellulose synthase complex.
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Affiliation(s)
- M A Ha
- Chemistry Department, Glasgow University, Glasgow G12 8QQ, UK, EPSRC Solid-state NMR Service, Durham University, Durham DH1 3LE, UK, and INRA Laboratoire de Pathologie Végétale, 16, rue Claude Bernard, 75231 Paris, France
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16
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Emons AM, Mulder BM. The making of the architecture of the plant cell wall: how cells exploit geometry. Proc Natl Acad Sci U S A 1998; 95:7215-9. [PMID: 9618565 PMCID: PMC22784 DOI: 10.1073/pnas.95.12.7215] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Cell wall deposition is a key process in the formation, growth, and differentiation of plant cells. The most important structural components of the wall are long cellulose microfibrils, which are synthesized by synthases embedded in the plasma membrane. A fundamental question is how the microfibrils become oriented during deposition at the plasma membrane. The current textbook explanation for the orientation mechanism is a guidance system mediated by cortical microtubules. However, too many contraindications are known in secondary cell walls for this to be a universal mechanism, particularly in the case of helicoidal arrangements, which occur in many situations. An additional construction mechanism involves liquid crystalline self-assembly [A. C. Neville (1993) Biology of Fibrous Composites: Development Beyond the Cell Membrane (Cambridge Univ. Press, Cambridge, U.K.)], but the required amount of bulk material that is able to equilibrate thermally is not normally present at any stage of the wall deposition process. Therefore, we have asked whether the complex ordered texture of helicoidal cell walls can be formed in the absence of direct cellular guidance mechanisms. We propose that they can be formed by a mechanism that is based on geometrical considerations. It explains the genesis of the complicated helicoidal texture and shows that the cell has intrinsic, versatile tools for creating a variety of textures. A compelling feature of the model is that local rules generate global order, a typical phenomenon of life.
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Affiliation(s)
- A M Emons
- Department of Plant Sciences, Laboratory of Plant Cytology and Morphology, Wageningen Agricultural University, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands
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Emons AMC, Kieft H. Comparison of embryogenic and non-embryogenic suspension cells of maize by means of freeze-fracturing. ACTA ACUST UNITED AC 1990. [DOI: 10.1016/0739-6260(90)90135-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Abstract
Direct freezing procedures have enabled us to visualize distinctive intramembrane particle ring structures in the cytoplasmic membranes of peritrichously flagellated bacteria by means of freeze-fracture electron microscopy. These structures were identified as flagellar motor components because their distribution matched that of flagella, and because they were absent in non-flagellated mutants of Escherichia coli. Particle rings were present in both the Gram-positive Streptococcus and the Gram-negative E. coli. In E. coli, a non-functional mocha operon produced flagellated but immotile cells lacking the particle rings. Simultaneous introduction of the motA and motB genes, led to recovery of both motility and the ring structures but neither gene alone was sufficient. The concomitant loss of the rings and motility is consistent with the ring particles having a central role in the flagellar motor.
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Affiliation(s)
- S Khan
- Department of Anatomy, Albert Einstein College of Medicine, Bronx, NY 10461
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19
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Occurrence of rosettes in the ER membrane of young Funaria hygrometrica protonemata. Naturwissenschaften 1987. [DOI: 10.1007/bf00446099] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Emons AM, van Maaren N. Helicoidal cell-wall texture in root hairs. PLANTA 1987; 170:145-151. [PMID: 24232872 DOI: 10.1007/bf00397882] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/1986] [Accepted: 08/08/1986] [Indexed: 06/02/2023]
Abstract
It is shown that root hairs of most aquatic plants have a helicoidal cell-wall texture. Cell walls of root hairs of the aquatic/marshland plant Ranunculus lingua, however, have an axial microfibril alignment. The occurrence of a helicoidal wall texture is not limited to root hairs of aquatic plants: the terrestrial plant Zebrina purpusii has a helicoidal root-hair wall texture, too. With the exception of the grasses, the occurrence of root hairs with helicoidal cell walls pertains to species with predetermined root-hair-forming cells, trichoblasts. The rotation mode of the helicoid is species-specific. The average angle between fibrils of adjacent lamellae varies from 23° to 40°. In Hydrocharis morsus-ranae, cortical microtubules have a net-axial orientation and thus do not parallel nascent microfibrils. The deposition of the helicoidal cell wall is discussed.
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Affiliation(s)
- A M Emons
- Department of Botany, University of Nijmegen, NL-6525 ED, Nijmegen, The Netherlands
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Kroh M, Knuiman B. Exocytosis in non-plasmolyzed and plasmolyzed tobacco pollen tubes : A freeze-fracture study. PLANTA 1985; 166:287-299. [PMID: 24241509 DOI: 10.1007/bf00401164] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/1985] [Accepted: 04/17/1985] [Indexed: 06/02/2023]
Abstract
Exocytosis occurring during deposition of secondary wall material was studied by freeze-fracturing ultrarapidly frozen non-plasmolyzed and plasmolyzed tobacco pollen tubes. The secondary wall of tobacco pollen tubes shows a random orientation of microfibrils. This was observed directly on fractures through the tube wall and indirectly as imprints of microfibrils on fracture faces of the plasma membrane of non-plasmolyzed tubes. About half of the plasmatic fracture faces from non-plasmolyzed and plasmolyzed pollen tubes carried hexagonal arrays of intramembraneous particles in between randomly distributed particles. Deposition of secondary wall material was often accompanied by an undulated plasma membrane and the presence of membrane-bound vesicles in invaginations of the plasma membrane, between the plasma membrane and secondary wall and-especially in plasmolyzed tubes-within the secondary wall of tube flanks and wall cap. The findings are discussed in connection with published schemes of membrane behaviour during exocytosis.
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Affiliation(s)
- M Kroh
- Department of Botany, University of Nijmegen, Toernooiveld, NL-6525 ED, Nijmegen, The Netherlands
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