Interactions of carbaryl with susceptible and multiresistant house flies (Diptera: Muscidae).

The in vivo and in vitro fate of [14C]carbaryl was compared in adult male and female house flies from an insecticide-susceptible (S) strain and a resistant (R) strain with multiple resistance to different classes of insecticides. Cuticular penetration of topically applied carbaryl (0.01 microgram/insect) was very rapid and rates were essentially the same among males and females of both strains. Rates of penetration were dramatically reduced as the concentration of applied carbaryl was increased over a range of 0.01-5.0 micrograms/insect. In vivo and in vitro tests demonstrated that the R strain had an enhanced capability for the metabolic degradation of carbaryl. In evaluations of topical toxicity and in vitro metabolic degradation, coadministration of the metabolic synergists piperonyl butoxide (a microsomal oxidase inhibitor) and S,S,S-tributyl phosphorothioate (DEF, an esterase inhibitor) with carbaryl provided conclusive evidence that microsomal oxidases were the major factor in enhanced metabolism and that hydrolytic enzymes had only a minor effect. Studies of the in vitro inhibition of acetylcholinesterase (AChE) activity by carbaryl demonstrated that there was no difference between males and females of a given strain and that the R strain AChE was considerably less sensitive to inhibition. These tests also indicated that homogenates of brains from the R strain contained more than one form of AChE with different sensitivities to the inhibitor. This information and results of toxicity tests with other insecticides suggest that the R strain is not homozygous in its resistance to carbaryl.     

Classifying genotypic data from plant breeding trials: a preliminary investigation using repeated checks

Summary Several subjective choices must be made when classifying genotypes based on data from plant breeding trials. One choice involves the method used to weight the contribution each environment makes to the classification. A second involves the use of either genotype-means for each environment or genotypevalues for each block, i.e., considering each block to be a different environment. Another involves whether environments (or blocks) in which genotypes are nonsignificantly different should be included or excluded from such classifications. An alternative to the use of raw or standardized data, is proposed in which each environment is weighted by a discrimination index (DI) that is based on the concept of repeatability. In this study the effect of three weighting methods (raw, standardized and DI), the choice of using environments or blocks, and the choice of including or excluding environments or blocks in which genotypic effects were not significant, were considered in factorial combination to give 12 options. A data set comprised of five check cultivars each repeated six times in each of three blocks at six environments was used. The effect of these options on the ability of a hierarchical clustering technique to correctly classify the repeats into five groups, each consisting of all the six repeats of a particular check cultivar, was investigated. It was found that the DI weighting method generally led to better recovery of the known structure. Using block data rather than environmental data also improved structure recovery for each of the three weighting methods. The exclusive use of environments in which genotypic effects were significant decreased structure recovery while the contrary generally occurred for blocks. The best structure recovery was obtained from the DI weighting applied to blocks (whether genotypes were significant or not).     

Plasmid-associated sensitivity of Bacillus thuringiensis to UV light.

Spores and vegetative cells of Bacillus thuringiensis were more sensitive to UV light than were spores or cells of plasmid-cured B. thuringiensis strains or of the closely related Bacillus cereus. Introduction of B. thuringiensis plasmids into B. cereus by cell mating increased the UV sensitivity of the cells and spores. Protoxins encoded by one or more B. thuringiensis plasmids were not involved in spore sensitivity, since a B. thuringiensis strain conditional for protoxin accumulation was equally sensitive at the permissive and nonpermissive temperatures. In addition, introduction of either a cloned protoxin gene, the cloning vector, or another plasmid not containing a protoxin gene into a plasmid-cured strain of B. thuringiensis all increased the UV sensitivity of the spores. Although the variety of small, acid-soluble proteins was the same in the spores of all strains examined, the quantity of dipicolinic acid was about twice as high in the plasmid-containing strains, and this may account for the differences in UV sensitivity of the spores. The cells of some strains harboring only B. thuringiensis plasmids were much more sensitive than cells of any of the other strains, and the differences were much greater than observed with spores.     

Crenation and cupping of the red cell: A new theoretical approach. Part II. Cupping

Typical, axisymmetrical cup shaped cells have been carefully measured and the shapes analyzed mathematically. The results show that the strain energy of a cup shaped cell is always higher than that of a biconcave cell except when the two layers of the membrane involved in resistance to bending are free to slide over one another. This is true whether intrinsic curvature of the membrane is positive, negative or zero. If the two layers can slide over one another, the cup shape becomes the lower energy form. Shear resistance, if appreciable, must cause the cup cell to buckle. Photomicrographs of cup shaped cells show buckled configurations characteristic of those of a partly deflated thin-walled rubber ball, which is a similar object having a low ratio of bending/shear strength.In light of these findings, the cup shape of the red cell can no longer be considered as evidence of intrinsic membrane curvature of opposite sign to that of the crenated cell, but appears to indicate a phase change either in the hydrophobic interior of the bimolecular membrane or in some equivalent interface.     

Phenotypic changes in the chemistry of Aspergillus nidulans: Influence of culture conditions on mycelial composition

A quantitative study was made of macromolecular (nucleic acids, protein), carbohydrate and mineral (magnesium, potassium and phosphorus) components of Aspergillus nidulans in glucose limited chemostat cultures, under varying conditions of dilution rate, temperature, pH and NaCl concentration.The overall mineral content showed greatest variation in response to changes in culture salinity, which also affected the mycelial carbohydrate content. Concomitant and opposite changes in the conent of cations and carbohydrates under conditions of increasing salinity may be interpreted in terms of mycelial osmoregulation. Slight variations in DNA content but gross fluctuations in the level of RNA were noted under the different cultural conditions examined. Co-ordinate changes in RNA and Mg²⁺ contents were evident only under certain conditions: dilution rate from 0.05–0.07 h^-1 or temperature from 22–30° C. The constant molar stoichiometry between RNA and Mg²⁺ characteristic of unicellular microorganisms was not a feature of fungal growth. The protein content was most affected by shifts of temperature and reached minimal values at 25 and 50° C.The growth environment had a marked influence on the protein synthesising activity of RNA, which increased eightfold as the dilution rate was increased from 0.02–0.175 h^-1, doubled within the temperature range 20–30° C and fell by 50% between 40 and 50° C. These observations are discussed in the context of the constant ribosomal efficiency in protein synthesis hypothesis.     

Bioaccumulation of silver by a multispecies community of bacteria

A stable community of bacteria that had unusually high tolerance of soluble silver was isolated from soil by chemostat enrichment. The community consisted of three bacteria: Pseudomonas maltophilia, Staphylococcus aureus and a coryneform organism. The pseudomonas was primarly responsible for the silver resistance. The tolerance of high silver concentrations, up to 100 mM Ag⁺, was greatly reduced when the community was grown in the absence of silver. Pseudomonas maltophilia comprised approximately 50% by numbers of the community when grown in chemostats in the presence or absence of Ag⁺ but large fluctuations occurred in population sizes of the other two bacteria; the S. aureus population was small (less than 1%) in the presence of Ag⁺ but comparised a third of the total numbers when Ag⁺ was omitted from the medium. Silver-resistant respiration of the silveradapted community was significant even when it was confronted with high concentrations of Ag⁺. In contrast the respiration of the coryneform organism and particularly S. aureus was highly sensitive to silver. The inhibition constants for silver-sensitive respiration were 0.78 mM and 0.04 mM for silver acclimatized and nonacclimatized communities respectively.The community had great capacity for silver bioaccumulation. Maximum concentrations of over 300 mg silver per g dry weight of biomass were recorded at an accumulation rate of 21 mg Ag⁺ h^-1 (g biomass)^-1. The extent of silver removal from solution was a function of initial concentration of silver; at low external concentrations (ca. 1 mM) all the silver was rapidly removed from solution, at high concentrations (ca. 12 mM) 84% removal occurred in 15 h.