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ABSTRACT: The actin cytoskeleton plays an important role in root hair development. It is involved in both the delivery of growth materials
to the expanding tip of root hairs and the regulation of the area of tip growth. This review starts with a discussion of the
techniques that are available to visualize the actin cytoskeleton in fixed and in live root hair cells, including their advantages
and drawbacks. We discuss the function that the actin cytoskeleton performs during tip growth of root hairs, focusing first
on filamentous actin organization during root hair development and the response of root hairs to the rhizobial signal molecule
Nod factor, which reveals the function of actin in root hair elongation. In addition, we discuss the role of actin binding
proteins in organizing the actin cytoskeleton.
05/2010: pages 211-232;
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ABSTRACT: Cell growth requires not only production of matter, but in addition, the targeting, transport, and delivery of this matter
to the site of cell expansion. Thus, a proper organization of cell structure, the cytoarchitecture, is a necessity for cell
elongation. The actual process of cell growth in a cell under turgor pressure is Golgi vesicle membrane insertion into the
plasma membrane and, at the same time, discharge of its contents into the existing cell wall at the site of wall expansion.
If one of these prerequisites is missing, growth will not occur. Thus, the Golgi vesicle is the unit of cell growth. The tip-growing
cell with robust cell expansion at a defined site is a model system “par excellence” to study this process. In this chapter,
we discuss the so-called tip-growth unit, i.e., the assemblage of nucleus, endoplasmic reticulum, polysomes, Golgi bodies,
Golgi vesicles, exocytosis machinery, clathrin-coated vesicles, endosomes, and mitochondria that specifically accumulate in
the (sub)apical region of tip-growing root hairs, all working in concert to enable apical growth. The last paragraph of this
chapter reviews methods used for the visualization of cellulose microfibrils.
05/2010: pages 27-44;
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ABSTRACT: We formulate, implement and test a robust method of determining sphere size distributions from finite thickness planar sections. The method uses a forward approach in which populations of proposed distributions are tested against the input data and refined using a genetic algorithm. This method is then applied to a real-world data set concerning endo- and exocytotic vesicles in the apical region of tip growing pollen tubes of Arabidopsis thaliana.
Journal of Microscopy 09/2008; 231(2):257-64. · 1.63 Impact Factor
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ABSTRACT: Exocytosis and endocytosis are pivotal in many biological processes, but remain difficult to quantify. Here we combine a new algorithm for estimating vesicle size with a detailed morphological analysis of tip-growing cells, in which exocytosis is highly localized and therefore more readily quantified. Cell preservation was rendered as life-like as possible by rapid freezing. This allowed us to produce the first estimates of exocytosis rates in the root hairs and pollen tubes of the model plant Arabidopsis. To quantify exocytosis and endocytosis rates during cell growth, we measured the diameter of vesicles located in the tips of Arabidopsis root hairs and pollen tubes and the widths of cell walls and the cell lumen in longitudinal thin transmission electron microscopic sections. In addition, we measured growth velocities of Arabidopsis root hairs and pollen tubes, using video microscopy. The number of exocytotic vesicles required for cell wall expansion, and the amount of excess membrane inserted into the plasma membrane to be internalized, were estimated from the values that were obtained. The amount of excess membrane that is inserted into the plasma membrane during cell growth was estimated as 86.7% in root hairs and 79% in pollen tubes. This membrane has to be recycled by endocytosis. From counting of the total number of vesicles that is present in thin EM sections through the pollen tube tip, we estimated the average number of vesicles that is present in the tip of pollen tubes. By calculating the total amount of membrane and cell wall material that is required for continued cell growth, assuming that all vesicles are exocytotic, we estimated that pollen tubes continue to grow for 33 s when delivery of vesicles to the tip is inhibited. We arrested vesicle delivery to the tip by application of cytochalasin D. After cytochalasin D application, pollen tubes continued to grow for 30-40 s, which is in the same range as the estimated value of 33 s and shows that in this time frame, the availability of exocytotic vesicles is not a limiting factor.
Journal of Microscopy 09/2008; 231(2):265-73. · 1.63 Impact Factor
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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.
Journal of Microscopy 09/2008; 231(2):192-200. · 1.63 Impact Factor
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ABSTRACT: We analysed the presence and localization of spectrin-like proteins in nuclei of various plant tissues, using several anti-erythrocyte spectrin antibodies on isolated pea nuclei and nuclei in cells. Western blots of extracted purified pea nuclei show a cross-reactive pair of bands at 220-240 kDa, typical for human erythrocyte spectrin, and a prominent 60 kDa band. Immunolocalization by means of confocal laser scanning microscopy reveals spectrin-like proteins in distinct spots equally distributed in the nucleoplasm and over the nuclear periphery, independent of the origin of the anti-spectrin antibodies used. In some nuclei tracks of spectrin-like proteins are also observed. No signal is present in nucleoli. The amount and intensity of signal increases when nuclei were extracted, successively, with detergents, DNase I and RNase A, and high salt, indicating that the spectrin-like protein is associated with the nuclear matrix. The labelling is similar in nuclei of various plant tissues. These data are the first that show the presence and localization of spectrin-like epitopes in plant nuclei, where they may stabilize specific interchromatin domains.
Cell Biology International 02/2000; 24(7):427-38. · 1.48 Impact Factor
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In: Abstracts of the ALW/FOM/VvBBMT-meeting on molecular and cellular biophysics. - Lunteren, The Netherlands : [s.n.], 2002.
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In: Biophysics: From molecules to cell. - Lunteren : [s.n.], 2000.
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In: Book of abstracts : 6th InternationalBotanical Microscopy Meeting, St. Andrews, March 25-29, 1999. - [S.l.] : [s.n.], 1999.
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Cell. Biol. Mol. Lett. 6 (2001).
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In: Abstracts 17th European Cytoskeleton Forum. - Nyon, Switzerland : [s.n.], 2002.
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Root hairs.
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The Plant Cell 14 (2002).
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Polarity in Plants.
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In: Biophysics: From molecules to cell. - Lunteren : [s.n.], 2000.
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In: Abstr. 12th FESPP Congress. - Budapest : [s.n.], 2000.
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ABSTRACT: exocyst is an octameric vesicle tethering complex that functions upstream of SNARE mediated exocytotic vesicle fusion with the plasma membrane. All proteins in the complex have been conserved during evolution, and genes that encode the exocyst subunits are present in the genomes of all plants investigated to date. Although the plant exocyst has not been studied in great detail, it is likely that the basic function of the exocyst in vesicle tethering is conserved. Nevertheless, genomic and genetic studies suggest that the exocyst complex in plants may have more diversified roles than that in budding yeast. In this review, we compare the knowledge about the exocyst in plant cells to the well-studied exocyst in budding yeast, in order to explore similarities and differences in expression and function between these organisms, both of which have walled cells
Journal of Integrative Plant Biology 52 (2010) 2.
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ABSTRACT: Cell division, growth, and cytoplasmic organization require a dynamic actin cytoskeleton. The filamentous actin (F-actin) network is regulated by actin binding proteins that modulate actin dynamics. These actin binding proteins often have cooperative interactions [1 and 2]. In particular, actin interacting protein 1 (AIP1) is capable of capping F-actin and enhancing the activity of the small actin modulating protein, actin depolymerising factor (ADF) in vitro [1 and 3]. Here, we analyze the effect of the inducible expression of AIP1 RNAi in Arabidopsis plants to assess AIP1s role in vivo. In intercalary growing cells, the normal actin organization is disrupted, and thick bundles of actin appear in the cytoplasm. Moreover, in root hairs, there is the unusual appearance of actin cables ramifying the root hair tip. We suggest that the reduction in AIP1 results in a decrease in F-actin turnover and the promotion of actin bundling. This distortion of the actin cytoskeleton causes severe plant developmental abnormalities. After induction of the Arabidopis RNAi lines, the cells in the leaves, roots, and shoots fail to expand normally, and in the severest phenotypes, the plants die. Our data suggest that AIP1 is essential for the normal functioning of the actin cytoskeleton in plant development
Current Biology 14 (2004) 2.
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ABSTRACT: ¿ The closely related proteins AtFH4 and AtFH8 represent the group Ie clade of Arabidopsis formin homologues. The subcellular localization of these proteins and their ability to affect the actin cytoskeleton were examined. ¿ AtFH4 protein activity was identified using fluorimetric techniques. Interactions between Arabidopsis profilin isoforms and AtFH4 were assayed in vitro and in vivo using pull-down assays and yeast-2-hybrid. The subcellular localization of group Ie formins was observed with indirect immunofluorescence (AtFH4) and an ethanol-inducible green fluorescent protein (GFP) fusion construct (AtFH8). ¿ AtFH4 protein affected actin dynamics in vitro, and yeast-2-hybrid assays suggested isoform-specific interactions with the actin-binding protein profilin in vivo. Indirect immunofluorescence showed that AtFH4 localized specifically to the cell membrane at borders between adjoining cells. Expression of an AtFH8 fusion protein resulted in GFP localization to cell membrane zones, similar to AtFH4. Furthermore, aberrant expression of AtFH8 resulted in the inhibition of root hair elongation. ¿ Taken together, these data suggest that the group Ie formins act with profilin to regulate actin polymerization at specific sites associated with the cell membrane
New Phytologist 168 (2005) 3.
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[show abstract]
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ABSTRACT: We analysed the presence and localization of spectrin-like proteins in nuclei of various plant tissues, using several anti-erythrocyte spectrin antibodies on isolated pea nuclei and nuclei in cells. Western blots of extracted purified pea nuclei show a cross-reactive pair of bands at 220–240 kDa, typical for human erythrocyte spectrin, and a prominent 60 kDa band. Immunolocalization by means of confocal laser scanning microscopy reveals spectrin-like proteins in distinct spots equally distributed in the nucleoplasm and over the nuclear periphery, independent of the origin of the anti-spectrin antibodies used. In some nuclei tracks of spectrin-like proteins are also observed. No signal is present in nucleoli. The amount and intensity of signal increases when nuclei were extracted, successively, with detergents, DNase I and RNase A, and high salt, indicating that the spectrin-like protein is associated with the nuclear matrix. The labelling is similar in nuclei of various plant tissues. These data are the first that show the presence and localization of spectrin-like epitopes in plant nuclei, where they may stabilize specific interchromatin domains.
Cell Biology International 24 (2000).
