The role of recombination in transfection of B. subtilis

Summary A comparative study of transfection with four different phage DNAs is being presented. Two types of transfection systems are distinguished, one with nearly linear dependence of the number of infective centers produced on the concentration of the phage DNA, the other type displaying multihit dose response. Studies of genetic recombination in transfection show that in systems of the latter type two (SPP 1) or three (SP 50) input genomes have to cooperate in a recombination event prior to replication. This obligatory process, termed primary recombination, is exclusively mediated by the host recombination system and cannot be effected by the phage recombination system.     

QUANTITATIVE CHANGES WITH AGE IN THE DNA CONTENT OF METHYLAZOXYMETHANOL-INDUCED MICROENCEPHALIC RAT BRAIN1

Abstract— DNA synthesis in methylazoxymethanol (MAM)-treated foetal brain was reduced during the first 3 days after the injection of the compound into the mother rat. The MAM-treated brain grew at almost the normal rate after this period, but the reduction in DNA persisted through maturity of the animal. This difference in DNA content between normal and microencephalic brain was restricted to the cerebral hemispheres. The major increase in DNA content of prenatal brain occurred in the cerebrum, whereas the postnatal increase took place in the cerebellum. jH-Labelled MAM was incorporated more extensively into foetal brain DNA than into RNA. The half-life of the MAM-modified nucleic acids was 4–5 days. We suggest that removal of necrotic cells from the brain may account for the rapid loss of label from nucleic acids.     

3D finite element analysis of uniaxial cell stretching: from image to insight

Mechanical forces play an important role in many microbiological phenomena such as embryogenesis, regeneration, cell proliferation and differentiation. Micromanipulation of cells in a controlled environment is a widely used approach for understanding cellular responses with respect to external mechanical forces. While modern micromanipulation and imaging techniques provide useful optical information about the change of overall cell contours under the impact of external loads, the intrinsic mechanisms of energy and signal propagation throughout the cell structure are usually not accessible by direct observation. This work deals with the computational modelling and simulation of intracellular strain state of uniaxially stretched cells captured in a series of images. A nonlinear elastic finite element method on tetrahedral grids was applied for numerical analysis of inhomogeneous stretching of a rat embryonic fibroblast 52 (REF 52) using a simplified two-component model of a eukaryotic cell consisting of a stiffer nucleus surrounded by a softer cytoplasm. The difference between simulated and experimentally observed cell contours is used as a feedback criterion for iterative estimation of canonical material parameters of the two-component model such as stiffness and compressibility. Analysis of comparative simulations with varying material parameters shows that (i) the ratio between the stiffness of cell nucleus and cytoplasm determines intracellular strain distribution and (ii) large deformations result in increased stiffness and decreased compressibility of the cell cytoplasm. The proposed model is able to reproduce the evolution of the cellular shape over a sequence of observed deformations and provides complementary information for a better understanding of mechanical cell response.     

Worldwide correlations of mechanical properties and green wood density

? Premise of the study: The density of wood is highly correlated with the ability of stems and roots to resist bending or twisting, which is important for evaluating the mechanical behavior of trees. It also provides a measure of carbon storage, which is an important variable in modeling ecosystem processes and tree construction costs. However, most measurements of the density and mechanical properties of wood have little direct bearing on understanding the biomechanics of living plants because they are based on kiln- or air-dried samples. ? Methods: Here, we present and analyze the relationships between four important mechanical properties (Young's modulus, the modulus of rupture, and the maximum strength in shearing and in compression) and the density of green wood (i.e., wood at 50% moisture content) from a worldwide, taxonomically broad spectrum of 161 species. ? Key results: These data indicate that each of the mechanical properties disproportionately increases across species with increasing green wood density, i.e., stems composed of denser green wood are disproportionately stiffer and stronger than stems with equivalent cross-sections composed of less dense green wood. ? Conclusions: Although denser wood may have a higher carbon construction cost, the mechanical benefits of denser woods likely outweigh the extra cost.     

Endothelin Receptor Antagonist Preserves Microvascular Perfusion and Reduces Ischemic Brain Damage Following Permanent Focal Ischemia

Synthesis and release of the potent vasoconstrictor peptide endothelin-1 (ET-1) increases following cerebral ischemia and has previously been shown to mediate the delayed hypoperfusion associated with transient global ischemia. In this study we assessed the impact of ET-1 on perfusion and infarct volume in a focal model of cerebral ischemia by use of the selective ET(A) receptor antagonist Ro 61-1790 (affinity for ET(A) receptor 1000 fold greater than ETB receptor). Control rats subjected to permanent middle cerebral artery occlusion (MCAO) showed extensive reductions in microvascular perfusion 4 h post-MCAO that were significantly attenuated by Ro 61-1790 pretreatment (10 mg/kg, i.v.). Ro 61-1790 concomitantly and significantly reduced the ischemic lesion volume in the same animals. This effect was maintained 24 h post-MCAO providing that the animals received additional i.v. injections of 5 mg/kg Ro 61-1790 at 5 h and 8 h after MCAO. These findings demonstrate that ET(A) receptor antagonism partially preserves tissue perfusion following focal ischemia and that this effect is associated with significant neuroprotection. The results also support the hypothesis that vasoactive mediators, and ET-1 in particular, are important contributors to the pathogenesis of cerebral ischemic injury.     

Damped oscillations of the giant reed Arundo donax (Poaceae)

The slender upright culms of the giant reed (Arundo donax L.) are often exposed to dynamic wind loads causing significant swaying. The giant reed has slightly tapered hollow stems (4-6 m high) with flat leaves and an extensive underground rhizomatous system with solid branches bearing adventitious roots. Quantitative analyses of videorecordings prove that A. donax responds to dynamic deflections of the stem with damped harmonic bending oscillations. The logarithmic decrement can be used to calculate the relative damping, as a measure of the plant's capacity to dissipate vibrational energy. Plants with leaves have a significantly higher damping compared to plants without leaves. A comparison of the relative damping of plants with and without leaves shows that this finding is only partly due to aerodynamic resistance of the leaves. Structural damping also contributes considerably to the overall damping of the foliate A. donax stem. By stepwise removal of the underground plant organs the influence of rhizome, roots, and soil on the vibrational behavior was determined. The data indicate that underground plant organs as well as leaf sheaths covering the nodes have no significant influence on damping.