Correlation between Supercoiling and Conformational Motions of the Bacterial Flagellar Filament

The bacterial flagellar filament is a very large macromolecular assembly of a single protein, flagellin. Various supercoiled states of the filament exist, which are formed by two structurally different conformations of flagellin in different ratios. We investigated the correlation between supercoiling of the protofilaments and molecular dynamics in the flagellar filament using quasielastic and elastic incoherent neutron scattering on the picosecond and nanosecond timescales. Thermal fluctuations in the straight L- and R-type filaments were measured and compared to the resting state of the wild-type filament. Amplitudes of motion on the picosecond timescale were found to be similar in the different conformational states. Mean-square displacements and protein resilience on the 0.1 ns timescale demonstrate that the L-type state is more flexible and less resilient than the R-type, whereas the wild-type state lies in between. Our results provide strong support that supercoiling of the protofilaments in the flagellar filament is determined by the strength of molecular forces in and between the flagellin subunits.     

Integration of transhumant pastoralism and irrigated agriculture in semi-arid East Africa

Agricultural development projects in the fertile and most well-watered areas of arid and semiarid Africa usually deny access to nomadic pastoralists whose production system and livelihood depend upon such areas in the dry season and during frequent droughts. The result can be degradation of range resources through overgrazing, and greater vulnerability of pastoralists. Recent calls for compatible land use schemes or nonexclusionary agricultural development projects in the context of pastoralist transhumance, suggest allowing pastoralists structured access to project sites in the dry season in order to utilize forage and water supplies. This paper examines the capacity of an irrigation scheme to support the seasonal influx of transhumant livestock in dry seasons of varying severity. The livestock carrying capacity of the existing mosaic of land use patterns and practices is used in the determination of the proportional areas of land use needed to absorb large seasonal concentrations of livestock.     

Real‐Time Investigation of Intercalation and Structure Evolution in Printed Polymer:Fullerene Bulk Heterojunction Thin Films

The complex intermixing morphology is critical for the performance of the nanostructured polymer:fullerene bulk heterojunction (BHJ) solar cells. Here, time resolved in situ grazing incidence X‐ray diffraction and grazing incidence small angle X‐ray scattering are used to track the structure formation of BHJ thin films formed from the donor polymer poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) with different fullerene derivative acceptors. The formation of stable bimolecular crystals through the intercalation of fullerene molecules between the side chains of polymer crystallites is investigated. Such systems exhibit more efficient exciton dissociation but lower photo‐conductance and faster decay of charges. On the basis of the experimental observations, intercalation obviously takes place before or with the formation of the crystalline polymer domains. It results in more stable structures whose volume remains constant upon further drying. Three distinct periods of drying are observed and the formation of unidimensional fullerene channels along the π‐stacking direction of polymer crystallites is confirmed.     

Physicochemical characterization of silicon-containing glycolipids by DSC,FT-Raman spectroscopy and X-ray diffraction

Derivatives of dimethylalkylchlorosilanes are novel substances which may be used in formulations for drug targeting. In order to design their properties it is essential to perform physicochemical characterization. For this purpose, a combination of differential scanning calorimetry (DSC), FT-Raman spectroscopy and X-ray diffraction is well suited. For the starting material dimethyloctadecylchlorosilane (DMOC), the assignment of Raman bands is discussed. The influence of sugar-containing head groups on the structures of the hydrocarbon chains of 1-O-(dimethyldodecylsilyl)-[2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside] and 1-O-(dimethyloctadecylsilyl)-[2,3,4,6-tetra-O-acetyl-beta-D-glucopyranoside] was investigated using the band position of the symmetric methylene mode. The temperature dependence of conformationally sensitive bands in the CH(2)-stretching region (2800-2900 cm(-1)), C-C-stretching region (1000-1150 cm(-1)) and CH(3)-rocking region (830-900 cm(-1)) was studied to characterize the state of order of the alkyl chains. Using X-ray diffraction, the repeating distances of layered structures was determined. The phase transitions occurring were found to be completely reversible. The subcell of DMOC shows an orthorhombic perpendicular packing structure in the crystalline state.     

Particle films for suppression of the codling moth (Lepidoptera: Tortricidae) in apple and pear orchards

Studies were conducted in 1997 and 1998 to evaluate the effects of three particle film formulations consisting of kaolin and adjuvants on neonate larvae, ovipositing adult females, and eggs of the codling moth, Cydia pomonella (L.). Neonate larval walking speed, fruit discovery rate, and fruit penetration rate on apple host plants coated with particle films were significantly lower than on host plants without particle films in laboratory assays. Females oviposited less on host plants covered with a particle film residue than on untreated plants in laboratory choice and no-choice tests. Hatch rate of codling moth neonate larvae was unaffected by particle films sprayed on host plants either before or after oviposition. Fruit infestation rates were significantly reduced on particle film-treated trees compared with untreated trees for both first- and second-generation codling moth in field trials in both apple and pear orchards. Particle films appear to be a promising supplemental control approach for codling moth in orchards where moth density is high, and may represent a stand-alone method where moth densities are lower.     

Functional constraints on nest characteristics of pebble mounds of breeding male hornyhead chub Nocomis biguttatus

Breeding male hornyhead chub Nocomis biguttatus constructed nests in areas with relatively high but less than maximum flow rate and greater than average water depth. Nests comprised c. 3000 pebbles for a total mass of 11 kg. Males selected pebbles of smaller diameter but higher density than pebbles in the immediate vicinity. Thus, nests balanced the risk of mound erosion and energetic cost of nest construction with the benefits of protection from egg predators and a stable internal flow rate for oxygenation. These data help establish environmental management goals for the conservation of N. biguttatus and the lotic ecosystems dependent upon them.     

Dynamic maintenance of asymmetric meiotic spindle position through Arp2/3-complex-driven cytoplasmic streaming in mouse oocytes

Mature?mammalian?oocytes?are?poised?for?completing?meiosis?II (MII) on fertilization by positioning the spindle close to an actomyosin-rich cortical cap. Here, we show that the Arp2/3 complex localizes to the cortical cap in a Ran-GTPase-dependent manner and nucleates actin filaments in the cortical cap and a cytoplasmic actin network. Inhibition of Arp2/3 activity leads to rapid dissociation of the spindle from the cortex. Live-cell imaging and spatiotemporal image correlation spectroscopy analysis reveal that actin filaments flow continuously away from the Arp2/3-rich cortex, driving a cytoplasmic streaming expected to exert a net pushing force on the spindle towards the cortex. Arp2/3 inhibition not only diminishes this actin flow and cytoplasmic streaming but also enables a reverse streaming driven by myosin-II-based cortical contraction, moving the spindle away from the cortex. Thus, the asymmetric MII spindle position is dynamically maintained as a result of balanced forces governed by the Arp2/3 complex.