A silver impregnation method for embedded central nervous tissue of the rat

A simple and yet reliable silver impregnation method, using potassium ferrocyanide, for demonstrating nervous tissue of the rat central nervous system embedded in paraffin or paraplast is described. The method reported here is compared and discussed with earlier techniques using potassium dicyanoargentate, potassium ferrocyanide and potassium ferricyanide.     

Predicting Carriers of Ongoing Selective Sweeps without Knowledge of the Favored Allele

Methods for detecting the genomic signatures of natural selection have been heavily studied, and they have been successful in identifying many selective sweeps. For most of these sweeps, the favored allele remains unknown, making it difficult to distinguish carriers of the sweep from non-carriers. In an ongoing selective sweep, carriers of the favored allele are likely to contain a future most recent common ancestor. Therefore, identifying them may prove useful in predicting the evolutionary trajectory—for example, in contexts involving drug-resistant pathogen strains or cancer subclones. The main contribution of this paper is the development and analysis of a new statistic, the Haplotype Allele Frequency (HAF) score. The HAF score, assigned to individual haplotypes in a sample, naturally captures many of the properties shared by haplotypes carrying a favored allele. We provide a theoretical framework for computing expected HAF scores under different evolutionary scenarios, and we validate the theoretical predictions with simulations. As an application of HAF score computations, we develop an algorithm (PreCIOSS: Predicting Carriers of Ongoing Selective Sweeps) to identify carriers of the favored allele in selective sweeps, and we demonstrate its power on simulations of both hard and soft sweeps, as well as on data from well-known sweeps in human populations.     

Catabolic instability,plasmid gene deletion and recombination in Alcaligenes sp. BR60

An Alcaligenes sp. BR60, isolated from surface runoff waters of the Hyde Park industrial landfill, contained a novel 85 kb catabolic plasmid (pBR60) functional in 3-chlorobenzoate (3Cba) degradation. The plasmid exhibited a spontaneous 3.2% frequency of deletion of a 14 kb fragment specifying 3Cba degradation. The deletion mutant BR40 and mitomycin C cured strains were not able to grow on 3Cba and had reversion frequencies of less than 10^-10 cell^-1 generation^-1. Transformation or conjugation of pBR60 into cured strains restored catabolic activity. An EcoRI, BgIII, HindIII and SaII restriction map of the deletion region was constructed, and EcoRI and HindIII fragments spanning the deletion region of the plasmid were cloned in pUC18. Conjugation of resistance plasmid R 68.45 into Alcaligenes sp. BR60, with selection on antibiotics, resulted in the elimination of pBR60 and maintenance of unaltered R68.45. In 30% of the exconjugants, 3Cba degradative capacity was retained, although variation in the regulation of 3Cba degradation was observed in these strains. Hybridization of deletion region fragments to BgIII digested total DNA of BR60 and the R68.45 cured exconjugants revealed the presence of pBR60 deletion region sequences in the chromosome of exconjugants. Hybridization also revealed a repeated sequence flanking the deletion region of pBR60. Selection on 4-chlorobenzoate as a sole source of carbon and energy resulted in the isolation of 4Cba⁺ mutants of Alcaligenes sp. BR60.Abbreviations 3 and 4 Cba chlorobenzoic acid isomers and growth phenotypes - HPLC high pressure liquid chromatography - ATCC American Type Culture Collection     

Xylanase and xylosidase activities in avocado fruit

The activities of xylanase and xylosidase were demonstrated in mature avocado (Persea americana Mill.) fruits from different cultivars. When monitored on the day of harvest during the season at 1-month intervals, xylanase activity decreased and xylosidase activity increased between January and February and then remained stable until May. When monitored during the ripening process (January harvest), xylanase activity was constant, and xylosidase activity reached a peak at the climax of ethylene evolution and cellulase activity. Xylanase, which originated from Trichoderma viride and was added to the medium in which avocado discs were incubated, induced ethylene evolution.     

Adenylate cyclase responses to sucrose stimulation in membranes of pig circumvallate taste papillae.

1. Typical adenylate cyclase (AC) responses to guanine nucleotides were found in membranes of pig circumvallate (CV) taste papillae. 2. Sucrose stimulated AC activity in the CV membranes and this stimulation was GTP dependent and tissue specific. 3. The stimulatory effect of sucrose in the CV membranes was dependent on the concentration of membranes used in the AC assay. 4. This study provides the first biochemical data on cellular transduction of taste in the pig, compares positively to preliminary results in cattle and supports recent suggestions for a role of cAMP in sweet taste transduction.     

Differing amounts of genetic polymorphism in testes and male accessory glands ofDrosophila melanogaster andDrosophila simulans

We surveyed genetic polymorphism by two-dimensional gel electrophoresis of male reproductive tract proteins in 20 isofemale lines each ofDrosophila melanogaster andDrosophila simulans. After classifying 244 such proteins ofDrosophila melanogaster and 271 ofDrosophila simulans by their distribution between testes and accessory glands within the reproductive tract, significant correlations were found between genetic polymorphism and tissue distribution. In both species, gland-specific proteins were significantly more polymorphic than testis-specific proteins, as well as those found in both testes and glands. Simultaneously, inDrosophila simulans, proteins found in roughly equivalent relative abundance in both testes and glands were significantly less variable than gland-specific and testis-specific proteins, as well as those with a quantitative difference in relative abundance between testes and glands. These correlations may reflect general differences in variability between extracellular and intracellular proteins and between proteins with broad as opposed to tissue-specific distributions.We thank the Natural Sciences and Engineering Research Council of Canada for financial support (Grant A0235 to R.S.S.).     

Stomatal Movement and Sucrose Uptake by Guard Cell Protoplasts of Commelina benghalensis L.

Sucrose concentration in guard cells of epidermal strips ofCommelina benghalensis increased with stomatal opening. Sucroseuptake patterns were investigated using guard cell protoplastsof C. benghalensis. Sucrose (0.5 mM) uptake into these protoplastswas sensitive to pH, with an optimum at pH 6. Uptake of sucroseinto guard cell protoplasts was inhibited by 2,4-dinitrophenol(DNP), diethylstilbestrol (DES) and (ptrifluoromethoxy)carbonylcyanide phenylhydrozone (FCCP), while DCMU and o-phenanthrolinehad no effect on the uptake of sucrose. Fusicoccin (FC) stimulatedsucrose influx. The influence of pH and the effect of the metabolicinhibitors on the sucrose uptake into the guard cell protoplastsare consistent with an energy dependent membrane-function. (Received July 7, 1986; Accepted September 26, 1986)     

Occurrence of B-chromosomes in diploid Allium stracheyi Baker and their elimination in polyploids

Summary In a population of Allium stracheyi Baker (2n=14) growing in Darjeeling both diploids and polyploids occur. The diploids contain B-chromosomes varying from 2–10 in number. Polyploids are conspicuous by absence of B-chromosomes. These in diploids are found in the pollen mother cells and also in the pollen, and some are provided with subterminal constriction.Diploid individuals when brought from Darjeeling to Calcutta (i. e. from temperate to tropical regions) became polyploid within a month and the B-chromosomes were simultaneously lost. In order to confirm this unexpected result, the transfer experiment has been repeated thrice with fresh collections in each case and selection of diploid bulbs after cytological observation. In all cases the result has been the same. In rare cases one or two B-chromosomes were found in the polyploid cells which might represent intermediate steps of the disappearance.B-chromosomes in diploids possibly help the individual to compete with polyploids by enlarging the adaptive capacity.The sudden polyploidisation by transfer from the mountains to the plains might have been the result of a shock due to the temperature difference. The high temperature may be deleterious for the reproduction of B-chromosomes, and their degeneration products possibly contribute to cytoplasmic changes and the spindle disturbances which effect polyploidisation.