Stress-induced Vortex Line Helixing Avalanches in the Plastic Flow of a Smectic A Liquid Crystal

Dynamic surface force measurements of the response of a smectic A to layer normal stress exhibited time dependence for topological events in which single smectic layers were added or removed. Single layer-sized jumps in sample thickness had a rapid component of duration of approximately 1 second that produced most of the change in separation, but that was heralded by a slow precursor acceleration in separation, which began up to a few hundred seconds before. This avalanche-like dynamic signature is consistent with a relaxation mechanism based on the Glaberson-Clem-Bourdon instability of vortex lines (screw dislocations) in the smectic order parameter.     

Lunar clinopyroxenes: chemical composition, structural state, and texture

Single-crystal x-ray diffraction, microprobe, optical and electron optical examinations of clinopyroxenes from Apollo 11 lunar samples 10003, 10047, 10050, and 10084 show that generally the crystals are composed of (001) augitepigeonite intergrowths in varying ratios. Transmission electron micrographs reveal abundant exsolution lamellae, many only 60 A thick. In addition to the phase inhomogeneities, primary chemical inhomogeneities are clearly demonstrated. There are reciprocal relationships between calcium and iron and between Ti(4+) + 2Ai and 2Si. Our evidence suggests that a chemically inhomogeneous subcalcic C2/c augite was the only primary pyroxene from which pigeonite later exsolved.     

Correlation of phytotoxin production with pathogenicity ofStreptomyces scabies isolates from scab infected potato tubers

A total of 23 isolates obtained from scab infected potato tubers representative of six sampling areas in Eastern and Central Canada and five ATCCStreptomyces strains were screened for pathogenicity on the basis of their ability to initiate scab development on aseptically cultured minitubers and plant generated tubers. The results were then correlated with any associated generation of the scab inducing phytotoxin, Thaxtomin A. In all cases a positive correlation was demonstrated between the pathogenicity of variousStreptomyces scabies isolates and their ability to produce the phytotoxin.     

Eradication of potato virus X from potato by ribavirin treatment of cultured potato shoot tips

Ribavirin treatment of cultured potato shoot tips was tested as a means of eradicating potato virus X (PVX) from two potato cultivars. Shoot tips were cultured on liquid medium containing 0, 1, 10 or 100μg/ml ribavirin. Cultures were evaluated periodically for viability, and scored for vigor on a relative growth scale. Developed plantlets were assayed for PVX by transmission tests toGomphrena globosa. Ribavirin treatment was phytotoxic at all tested concentrations, and lethal to all cultivars treated at 100 μg/ml. Treatment also delayed plantlet development by up to 2 months at 1 and 10 μg/ml as compared with nontreated controls. PVX assays indicated that 80 and 83% of the plantlets were free of PVX following treatment with 10 μg/ml for cultivars Russet Burbank and Red McClure, respectively. Five and 6% of the plantlets developed from the 1 μg/ml treatment were PVX-free, whereas 0 and 2% of the controls were PVX-free for the same cultivars. Six to 8 months were required to develop plants from shoot-tip cultures treated with 10 μg/ml ribavirin.     

Sulfated-polysaccharide fraction from red algae Gracilaria caudata protects mice gut against ethanol-induced damage

The aim of the present study was to investigate the gastroprotective activity of a sulfated-polysaccharide (PLS) fraction extracted from the marine red algae Gracilaria caudata and the mechanism underlying the gastroprotective activity. Male Swiss mice were treated with PLS (3, 10, 30 and 90 mg·kg(-1), p.o.), and after 30 min, they were administered 50% ethanol (0.5 mL/25 g(-1), p.o.). One hour later, gastric damage was measured using a planimeter. Samples of the stomach tissue were also obtained for histopathological assessment and for assays of glutathione (GSH) and malondialdehyde (MDA). Other groups were pretreated with l-NAME (10 mg·kg(-1), i.p.), dl-propargylglycine (PAG, 50 mg·kg(-1), p.o.) or glibenclamide (5 mg·kg(-1), i.p.). After 1 h, PLS (30 mg·kg(-1), p.o.) was administered. After 30 min, ethanol 50% was administered (0.5 mL/25 g(-1), p.o.), followed by sacrifice after 60 min. PLS prevented-ethanol-induced macroscopic and microscopic gastric injury in a dose-dependent manner. However, treatment with l-NAME or glibenclamide reversed this gastroprotective effect. Administration of propargylglycine did not influence the effect of PLS. Our results suggest that PLS has a protective effect against ethanol-induced gastric damage in mice via activation of the NO/K(ATP) pathway.     

End-to-end stacking and liquid crystal condensation of 6 to 20 base pair DNA duplexes

Short complementary B-form DNA oligomers, 6 to 20 base pairs in length, are found to exhibit nematic and columnar liquid crystal phases, even though such duplexes lack the shape anisotropy required for liquid crystal ordering. Structural study shows that these phases are produced by the end-to-end adhesion and consequent stacking of the duplex oligomers into polydisperse anisotropic rod-shaped aggregates, which can order into liquid crystals. Upon cooling mixed solutions of short DNA oligomers, in which only a small fraction of the DNA present is complementary, the duplex-forming oligomers phase-separate into liquid crystal droplets, leaving the unpaired single strands in isotropic solution. In a chemical environment where oligomer ligation is possible, such ordering and condensation would provide an autocatalytic link whereby complementarity promotes the extended polymerization of complementary oligomers.     

An improved in vitro rearing system for the human head louse allows the determination of resistance to formulated pediculicides

An improved in vitro rearing system, based on a silicone-reinforced Parafilm^® M membrane, human hair tufts and reconstituted human blood, enabled the large-scale rearing of pediculicide-susceptible (EC-HL) and resistant (SF-HL and BR-HL) strains of human head lice. Developmental time differed for early instars but differences became synchronized as lice matured. Mean survivorship amongst the three strains reared in vitro were not significantly different when compared to EC-HL and SF-HL reared in vivo. The efficacies of three pediculicidal products were assessed under semi-clinical conditions using a modified version of the in vitro rearing system. Treatments of 1% permethrin in acetone, Nix^®, Rid^® or Pronto^® Plus to hair tufts following manufacturer’s instructions were highly efficacious (100% mortality) on EC-HL but differentially efficacious (62.2-84.4% mortality) on SF-HL examined eight days post-treatment. SF-HL that survived the first treatment received an identical second treatment eight days following the first treatment. Survivors (13.3-30.0%) developed to adults (10th-11th day following first treatment) and females successfully laid fertile eggs that developed to first instars. These results confirm resistance to permethrin- and pyrethrin-based pediculicide formulations in SF-HL when assessed under semi-clinical conditions and validates resistance previously determined using filter-paper contact bioassays and unformulated insecticides.     

Resistance in the highly DDT-resistant 91-R strain of Drosophila melanogaster involves decreased penetration,increased metabolism,and direct excretion

Resistance to 4,4′-dichlorodiphenyltrichloroethane (DDT) in the 91-R strain of Drosophila melanogaster is extremely high compared to the susceptible Canton-S strain (>1500 times). In addition to enhanced oxidative detoxification, the 91-R strain also has a reduced rate of DDT penetration, increased levels of reductive and conjugative metabolism, and substantially more excretion than the Canton-S strain. Contact penetration of DDT was ∼30% less with 91-R flies, which also had significantly more cuticular hydrocarbons and a thicker, more laminated cuticle compared to Canton-S flies, possibly resulting in penetration differences. DDT was metabolized ∼1.6-fold more extensively by 91-R than Canton-S flies, resulting in dichlorodiphenyldichloroethane (DDD), two unidentified metabolites and polar conjugates being formed in significantly greater amounts. 91-R flies also excreted ∼4-fold more DDT and metabolites than Canton-S flies. Verapamil pretreatment reduced the LD₅₀ value for 91-R flies topically dosed with DDT by a factor of 10-fold, indicating that the increased excretion may involve, in part, ATP-binding cassette (ABC) transporters. In summary, DDT resistance in 91-R is polyfactorial and includes reduced penetration, increased detoxification and direct excretion.     

Effects of acorn size and mass on seedling quality of northern red oak (<Emphasis Type="Italic">Quercus rubra</Emphasis>)

Oaks are not sustainable in many upland temperate forests because of poor recruitment resulting from natural regeneration. Artificial regeneration is an alternative to natural regeneration, but is difficult, in part, due to large variation in seedling quality. In this study, we examined the effects of acorn size and mass on nursery seedling morphological parameters commonly used to quantify seedling quality, and we determined if genetic factors affected these relationships. Acorns were collected from six open-pollinated orchard trees (i.e., six half-sib families), and were separated into six size classes based on acorn diameter (ranging from 1.3 to 2.5 cm). Samples from each size class were weighed for total fresh mass. Acorns were sown in a commercial bareroot nursery in Polk County, Tennessee, USA, and seedlings were grown for 1 year using nursery protocols to maximize growth. Seedling survival was generally not affected by acorn size class or mass, except one family had higher survival in the larger acorn size classes. Five of the six families had no discernable relationship between acorn size class and seedling size. Acorn mass was positively related to seedling morphology, but relationships were weak (R²?≤?0.11) and biologically insignificant. Neither acorn size nor mass could be used reliably to predict seedling survival or morphological indicators of seedling quality. We hypothesized that results were affected by an unusually long growing season and advanced fertilization regimes at the nursery, which may have negated acorn size/mass effects on seedling growth. Family affected relationships between acorn size/mass and seedling morphology, indicating that family selections could improve overall seedling quality.