Extensive Reorientation Research Articles

Changes in the orientations of cellulose microfibrils during the development of collenchyma cell walls of celery (Apium graveolens L.).

During development, cellulose microfibrils in collenchyma walls become increasingly longitudinal, as determined by small-angle X-ray scattering, despite the walls maintaining a fine structure indicative of a crossed-polylamellate structure. Collenchyma cells have thickened primary cell walls and provide mechanical support during plant growth. During their development, these cells elongate and their walls thicken considerably. We used microscopy and synchrotron small-angle X-ray scattering to study changes in the orientations of cellulose microfibrils that occur during development in the walls of collenchyma cells present in peripheral strands in celery (Apium graveolens) petioles. Transmission electron microscopy showed that the walls consisted of many lamellae (polylamellate), with lamellae containing longitudinally oriented cellulose microfibrils alternating with microfibrils oriented at higher angles. The lamellae containing longitudinally oriented microfibrils predominated at later stages of development. Nevertheless, transmission electron microscopy of specially stained, oblique sections provided evidence that the cellulose microfibrils were ordered throughout development as crossed-polylamellate structures. These results are consistent with our synchrotron small-angle X-ray scattering results that showed the cellulose microfibrils become oriented increasingly longitudinally during development. Some passive reorientation of cellulose microfibrils may occur during development, but extensive reorientation throughout the wall would destroy ordered structures. Atomic force microscopy and field emission scanning electron microscopy were used to determine the orientations of newly deposited cellulose microfibrils. These were found to vary widely among different cells, which could be consistent with the formation of crossed-polylamellate structures. These newly deposited cellulose microfibrils are deposited in a layer of pectic polysaccharides that lies immediately outside the plasma membrane. Overall, our results show that during development of collenchyma walls, the cellulose microfibrils become increasingly longitudinal in orientation, yet organized, crossed-polylamellate structures are maintained.

Mesozoic hydrothermal impact on Rotliegende and Bunter immature sandstones of the High Rhine trough and its adjacent eastern area (southern Black Forest, Germany)

The Mesozoic hydrothermal and geodynamic evolution of a complex region of the European crust is studied here on immature and highly reactive Rotliegende and Bunter sandstones of the intramontane High Rhine trough (southern Black Forest) and its adjacent eastern area bounded by the Upper Rhine Graben and the Alpine foreland. Microscopic observations outline varied degrees of illitization of detrital feldspar grains, muscovite flakes and illite particles. XRD analysis shows that the clay fractions are dominated by illite with minor illite/smectite mixed-layered minerals of R3 and R1 ordering. The chemical composition of these minerals is controlled by precursor minerals, since the illitic material inherited its chemical components from detrital muscovite and illite. Towards the centre of the trough, the sandstones were more strongly affected by the hydrothermal impact, showing extensive replacement of feldspar grains by Al-rich illite. K–Ar dating of the authigenic illite-type material points to multiple hydrothermal alteration episodes. A Late Jurassic event at 147 Ma seems to have affected extensively the study area, especially towards the centre of the trough. At the periphery of the trough, relics of an Early Jurassic activity are likely preserved. An additional Early Cretaceous hydrothermal event seems to have occurred locally near Schopfheim and next to the Rhine Graben boundary fault long before its main rifting phase. The 147 Ma event was obtained also nearby in the previously investigated Breisgau–Schramberg, Offenburg–Teinach and Baden–Baden troughs and is characteristic for the Black Forest and some other areas outside this region. It concludes obviously a period of regional hydrothermal activities between 160 and 145 Ma, whereas the Early Jurassic and Cretaceous signatures are also known throughout Central and Western Europe, suggesting repeated fluid pulses. The hydrothermal flows were controlled by reactivated basement faults due to periods of extensive reorientation of the tectonic stress during the break-up of Pangaea. Illitization was triggered by hot and low saline solutions of about 180 °C and < 10 wt.% NaCl eq, whereas a later fluid pulse of about 80 °C and >20 wt.% NaCl eq caused quartz overgrowth. Fluid flows delivered by the long lasting orogeny of the nearby Alps were probably limited towards the Black Forest. Becoming part of the European margin of the Tethys in the Mesozoic, the pre-Alp area evidently developed a separate fluid-flow system.

Multiscale Mechanics of Fibrin Clots

Although we know a great deal about the structure, properties and many functions of fibrin(ogen), we still know very little about the microscopic and molecular origins of the clot's mechanical properties, even though they are necessary for its functions, since hemostasis is essentially a mechanical process. In addition, it has been shown that individuals who have myocardial infarction at an early age tend to form very stiff clots. We have carried out studies at different levels of structure and integrated the results through a model that demonstrates that fibrin clot mechanical properties are manifestations of the observed mechanical characteristics of fibrin(ogen) molecules. By stretching whole fibrin clots with an extensional rheometer, we observed fibrin's remarkable extensibility with a mechanical response that was initially linear with an increase in stiffness at larger elongation, above two-fold. These results are consistent with the large extensibility that has been observed in single fibrin fibers and may also play a role in the mechanics of blood clots at high strain, as in arterial blood flow. Furthermore, we found that protein structural transitions are required even at lower elongations. Some of the corresponding structural changes in the clots with stretching up to about four-fold were observed by electron microscopy. Scanning electron microscopy of the clots revealed extensive reorientation of the fibers making up the clots in the direction of applied stress. The orientational order was quantified from the scanning electron microscope images using a custom, automated image analysis algorithm that calculates a network order parameter, revealing a high degree of alignment for stretched, initially unoriented fibrin gels. Crosssections of stretched clots were examined by transmission electron microscopy. The most striking change observed was a huge (up to 10-fold) decrease in volume with stretching, with aggregation or bundling of fibers. Basic features of the mechanics of single fibrin fibers are known. These measurements have recently been extended to the level of single molecules using atomic force microscopy. When factor XIIIa-ligated fibrinogen oligomers were stretched by atomic force microscopy, the coiled-coils were found to unfold first under force. Until now, these observations at the molecular and fiber levels have not been correlated with the behavior of whole fibrin clots. These levels of structure were bridged through small angle X-ray fiber diffraction patterns obtained from fibrin clots, since the primary peaks in the X-ray diffraction pattern correspond to the characteristic 22.5 nm repeat distance in fibrin fibers arising from the molecular packing. In contrast to some earlier reported results, there was no change in periodicity with stretching. Instead, these peaks broadened as the sample was stretched, consistent with structural disruptions like protein unfolding while the position of the 22.5 nm peak corresponding to the fibrin repeat remained constant. Since all of these measurements are quantitative, we developed a constitutive model, including all of the features observed, that suggests that the whole clot and fiber mechanical properties are a consequence of coiled-coil unfolding. All together, this study has allowed us to develop a truly multiscale understanding of fibrin mechanics that reveals how clots or thrombi, even though they are made up of relatively stiff fibers, can still have large extensibility that allows them to withstand large strains and open and permeable structures such that they are readily lysed. Understanding how the network, fiber, and molecular properties give rise to fibrin mechanics could contribute to designs of tougher or more extensible clots or lead to new strategies for breaking up clots or making them less occlusive.

Direct observation of the solvent reorientation dynamics in the “twisted” intramolecular charge-transfer process of cyanophenyldisilane–water cluster by transient infrared spectroscopy

The solvent reorientation dynamics of the intramolecular charge-transfer (ICT) process of the (p-cyanophenyl)pentamethyldisilane-H(2)O (CPDS-H(2)O) cluster was investigated by transient infrared (IR) absorption spectroscopy. Transient IR bands of two distinct charge-transfer (CT) states appeared in both the OH and the CN-stretching vibration regions. Analyses of the IR spectra and the time profiles of the transient bands revealed that the ICT process of the CPDS-H(2)O cluster proceeds in two steps. The first step is a transition from a photo-prepared locally excited (LE) state to the CT state, which is accompanied by a minor reorientation of the H(2)O moiety. In contrast, the second step is an extensive reorientation process of the H(2)O molecule in the CT state. These two reorientation processes exhibit very distinct pico- and nano-second time scales. In the latter case, a relatively slow time constant of 2 ns was related to a large geometric change in the orientation.

Affine Versus Non-Affine Fibril Kinematics in Collagen Networks: Theoretical Studies of Network Behavior

The microstructure of tissues and tissue equivalents (TEs) plays a critical role in determining the mechanical properties thereof. One of the key challenges in constitutive modeling of TEs is incorporating the kinematics at both the macroscopic and the microscopic scale. Models of fibrous microstructure commonly assume fibrils to move homogeneously, that is affine with the macroscopic deformation. While intuitive for situations of fibril-matrix load transfer, the relevance of the affine assumption is less clear when primary load transfer is from fibril to fibril. The microstructure of TEs is a hydrated network of collagen fibrils, making its microstructural kinematics an open question. Numerical simulation of uniaxial extensile behavior in planar TE networks was performed with fibril kinematics dictated by the network model and by the affine model. The average fibril orientation evolved similarly with strain for both models. The individual fibril kinematics, however, were markedly different. There was no correlation between fibril strain and orientation in the network model, and fibril strains were contained by extensive reorientation. As a result, the macroscopic stress given by the network model was roughly threefold lower than the affine model. Also, the network model showed a toe region, where fibril reorientation precluded the development of significant fibril strain. We conclude that network fibril kinematics are not governed by affine principles, an important consideration in the understanding of tissue and TE mechanics, especially when load bearing is primarily by an interconnected fibril network.

INTERCULTURAL HERMENEUTICS-CONTEXTUAL EXEGESIS

A MODEL FOR 21ST CENTURY EXEGESIS [*] 1. On the situation of from an ecumenical perspective The ecumenical movement began over a hundred years ago with the enthusiastic vision of evangelizing the whole world within a generation. The world mission conference in Edinburgh in 1910 brought together 1200 representatives of missionary societies and churches, but these included only 18 representatives of young churches in the Southern hemisphere. It was recognized that to reach this lofty goal, an important task would be translation of the Bible into local languages, especially in Asia and Africa. This was undertaken in response to a strong impetus from the national Bible societies which had been founded in the 19th century, and in continuation of the work which they had already done. In the decades around the turn of the century, Protestant missions distributed hundreds of thousands of Bibles in the Southern hemisphere. [1] As a result of these efforts, the world mission conferences which followed could record a steadily growing number of delegates from the colonial regions, with a sharp increase in their participation in the World Council of Churches after the end of the colonial era. For the churches, the period of decolonization was marked at first by the complete handing over of church leadership functions to indigenous theologians. These theologians, however, though trained in European theology, soon began thinking in terms of their own cultures and life contexts, and undertook to try to inculturate and contextualize the gospel. In addition, a large number of genuinely indigenous churches were founded, in some cases theologically very different from one another. Theologians from Africa, Asia and Latin America began to organize themselves into national, continental (e.g. the All-African Conference of Churches, AACC) and intercontinental conferences (e.g. the Ecumenical Association of Third World Theologians, EATWOT), from wh ich they could confidently bring their own perspectives into the ecumenical debate. At the end of the 20th century, we are beginning to speak of a shift in the centre of gravity of Christianity [2] away from the increasingly rich nations of the Northern hemisphere, towards the populations of the economically dependent nations of the Southern hemisphere. Even though the majority of Christians today do live in Africa, Asia and Latin America -- and not in Europe and North America, as they did at the beginning of the 20th century -- this observation is not true only from a numerical viewpoint. The interpretation of the Bible in the countries of the South, and the accompanying developments in worship, teaching and the life of faith, point to an extensive re-orientation and re-focussing of Christianity. In spite of all confessional differences, a common denominator of churches and theology in the Southern hemisphere could be said to be their perspective as economically disadvantaged and impoverished peoples who live by their unshakeable experience of the presence of God. 2. Challenges After almost 200 years of efforts by national and international Bible societies, the Bible has been partially or fully translated into a great many existing languages. These translations represent interpretations which are the result of processes of understanding taking place within specific socio-linguistic contexts. In view of the diversity of contemporary inculturation processes, one may ask how Christians are to communicate among themselves. Even though ecumenical as a whole represents a living commentary on the one Bible, it can hardly be considered a uniform community of readers worldwide. Instead, the ecumenical community must be seen as made up of many communities of interpretation, each with its own specific cultural and contextual characteristics. One faith -- different faces. But can the members of the ecumenical Christian family look one another in the eye and see in the face of the other, which may be deep black, pale white or in-between, a sister or brother who is their equal? …

Large-Scale Movement of Elongation Factor G and Extensive Conformational Change of the Ribosome during Translocation

Elongation factor (EF) G promotes tRNA translocation on the ribosome. We present three-dimensional reconstructions, obtained by cryo–electron microscopy, of EF-G-ribosome complexes before and after translocation. In the pretranslocation state, domain 1 of EF-G interacts with the L7/12 stalk on the 50S subunit, while domain 4 contacts the shoulder of the 30S subunit in the region where protein S4 is located. During translocation, EF-G experiences an extensive reorientation, such that, after translocation, domain 4 reaches into the decoding center. The factor assumes different conformations before and after translocation. The structure of the ribosome is changed substantially in the pretranslocation state, in particular at the head-to-body junction in the 30S subunit, suggesting a possible mechanism of translocation.

ON BASIC DIRECTIONS OF ENVIRONMENTAL POLICY IN THE USSR

A brief review of recent developments in environmental thinking in the USSR sets the stage for a critique of an important (if implicit) tenet of the policy of intensification in economic development—that the spatial concentration of productive capacity and population in area cities and urban agglomerations will promote environmental protection efforts by affording economics of scale and agglomeration in the development of pollution control technologies. Comprehensive, broadly based environmental studies must be undertaken in conjunction with analyses of the spatial efficiency of production, so that such assumptions can be tested prior to any extensive reorientation of population and economic activity (translated by Andrew R. Bond).