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Transverse Orientation (transverse + orientation)
Selected AbstractsMicrotubule-dependent motility and orientation of the cortical endoplasmic reticulum in elongating characean internodal cellsCYTOSKELETON, Issue 3 2009Ilse Foissner Abstract Motility of the endoplasmic reticulum (ER) is predominantly microtubule- dependent in animal cells but thought to be entirely actomyosin-dependent in plant cells. Using live cell imaging and transmission electron microscopy to examine ER motility and structural organization in giant internodal cells of characean algae, we discovered that at the onset of cell elongation, the cortical ER situated near the plasma membrane formed a tight meshwork of predominantly transverse ER tubules that frequently coaligned with microtubules. Microtubule depolymerization increased mesh size and decreased the dynamics of the cortical ER. In contrast, perturbing the cortical actin array with cytochalasins did not affect the transverse orientation but decreased mesh size and increased ER dynamics. Our data suggest that myosin-dependent ER motility is confined to the ER strands in the streaming endoplasm, while the more sedate cortical ER uses microtubule-based mechanisms for organization and motility during early stages of cell elongation. We show further that the ER has an inherent, NEM-sensitive dynamics which can be altered via interaction with the cytoskeleton and that tubule formation and fusion events are cytoskeleton-independent. Cell Motil. Cytoskeleton 2009. © 2009 Wiley-Liss, Inc. [source] The stress,life fatigue behaviour of aluminium alloy foamsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2000McCullough The tension,tension and compression,compression nominal stress versus fatigue life responses of Alulight closed cell aluminium alloy foams have been measured for the compositions Al,1Mg,0.6Si and Al,1Mg,10Si (wt %), and for relative densities in the range 0.1,0.4. The fatigue strength of each foam increases with the relative density and with the mean applied stress, and is greater for the transverse orientation than for the longitudinal orientation. Under both tension,tension and compression,compression loading the dominant cyclic deformation mode appears to be material ratchetting; consequently, the fatigue life is highly sensitive to the magnitude of the applied stress. A micromechanical model is given to predict the dependence of life upon stress level and relative density. Panels containing a central hole were found to be notch insensitive for both tension,tension and compression,compression fatigue loading: the net-section strength equals the unnotched strength. [source] Disruption of Cortical Microtubules by Overexpression of Green Fluorescent Protein-Tagged ,-Tubulin 6 Causes a Marked Reduction in Cell Wall SynthesisJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 1 2006David H. Burk Abstract It has been known that the transverse orientation of cortical microtubules (MTs) along the elongation axis is essential for normal cell morphogenesis, but whether cortical MTs are essential for normal cell wall synthesis is still not clear. In the present study, we have investigated whether cortical MTs affect cell wall synthesis by direct alteration of the cortical MT organization in Arabidopsis thaliana. Disruption of the cortical MT organization by expression of an excess amount of green fluorescent protein-tagged ,-tubulin 6 (GFP-TUA6) in transgenic Arabidopsis plants was found to cause a marked reduction in cell wall thickness and a decrease in the cell wall sugars glucose and xylose. Concomitantly, the stem strength of the GFP-TUA6 overexpressors was markedly reduced compared with the wild type. In addition, expression of excess GFP-TUA6 results in an alteration in cell morphogenesis and a severe effect on plant growth and development. Together, these results suggest that the proper organization of cortical MTs is essential for the normal synthesis of plant cell walls. (Managing editor: Wei Wang) [source] Effect of steady torque twisting on the orientation of cortical microtubules in the epidermis of the sunflower hypocotylPLANT BIOLOGY, Issue 4 2008J. Elsner Abstract Orientation of cortical microtubules (cMTs) is suggested to be affected by mechanical stress existing in cell walls. However, in mutants exhibiting helical (chiral) growth, there is a correlation between orientation of cMTs in outer tissues and helical growth direction. The aim of this research was to examine the effect of a chiral mechanical stimulation on cMTs. For this purpose, the orientation of cMTs was investigated in hypocotyls subjected to either a right- or a left-handed twist, resulting from a steady torque. cMTs were visualised in fixed material using the immunofluorescence method. The cMTs in untouched control hypocotyls were mostly transverse with respect to the cell long axis. In immobilised, but not twisted control hypocotyls, the transverse orientation was also most frequent, while applied twisting resulted in a change in cMT orientation from transverse to oblique. The data provide additional evidence that changes in tissue stress can be reorganized by cortical microtubules. [source] Biomechanics of the Fractured Medial Coronoid Process and the Isolated Anconeal Process in the Canine Elbow JointANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 2005J. Maierl Introduction:, Elbow dysplasia is one of the most important orthopaedic diseases of the canine elbow joint. The medial coronoid process (MCP) and the anconeal process (AP) are involved with a high incidence. Aims:, The aim of this study was to clarify whether these processes are especially loaded resulting in osteoarthrosis. Material and Methods:, Elbow joints were examined from dogs of various breeds, with a body weight over 20 kg and an age ranging from 1 to 12 years. Only joints without damage to the articular cartilage have been included in this investigation. Articular surfaces have been evaluated macroscopically, subchondral bone density (long-term loading) and split-lines (long-term tensile loading) have been determined. Results:, In the humeral fossa olecrani, there was a distinct impression on the inner side of the lateral compared to the medial epicondyle. In the ulna, the MCP was much greater than the lateral coronoid indicating that the medial process has to support the humeral condyle to a higher extent. Subchondral split lines with a transverse orientation in the fossa olecrani gave evidence of long-term transverse tensile loading in this area. Split lines on the MCP were oriented radially as if the lateral edge was bent downwards. Subchondral bone density in the fossa olecrani was higher towards the lateral epicondyle in comparison to the medial. Furthermore, there was a bone density maximum on the medial part of the humeral condyle opposite of the MCP with its very high density. Discussion:, Gait analyses showed that there is a transverse, medially oriented force of up to 4% bodyweight acting on the paw during midstance. As the carpus is stable when slightly hyperextended during midstance loading there is a long lever arm from the ground up to an assumed rotation centre in the depth of the trochlear notch. The medially directed ground reaction force slightly rotates the forearm inwards causing a bending moment about the elbow joint, which leads to an increased pressure of the AP and the MCP. This bending in addition to sagittal loading is the reason for the high susceptibility of the MCP and AP. [source] Role of particle size in till-fabric characteristics: systematic variation in till fabric from Vestari-Hagafellsjökull, IcelandBOREAS, Issue 4 2007Simon J. Carr Till-fabric analysis has often been used to interpret glacier flow directions and subglacial dynamics using vector-based statistics, but recent data suggest that such analysis may also effectively indicate former glacier dynamics. The results of a fabric investigation of subglacially strained till deposited during a surge of Vestari-Hagafellsjökull, Iceland, are presented. Till fabric was collected at four sites within a limited area where ice-flow direction during deposition was known from subglacial bedforms at the site. Analysis was carried out on elongate grains (axial ratio <1.5:1) at seven size fractions, with the a-axis length ranging from 0.25 to 32 mm. The largest grains tend to be parallel to ice flow, whereas smaller grains reflect a mix of parallel and transverse orientations. The implications of these data for the role and validity of till-fabric analysis are discussed, with reference to vector analyses and the compilation of fabric shape envelopes. It is noted that, in contrast to laboratory experimental data, neither March nor Jeffery mechanisms explain the fabric configurations reported. It is concluded that a standardized approach is necessary for collecting fabric data, and in many situations analysis of data populations at a range of particle sizes is desirable. [source] | ||||||||||