Sperm ultrastructure of five species of the Neotropical ant genus Pseudomyrmex (Hymenoptera: Formicidae)

The seminal vesicles of adult males of five species of Pseudomyrmex were prepared for light and transmission electron microscopy. The Pseudomyrmex spermatozoa are long and slender with similar morphology. The head region has an acrosome and a nucleus. In all the studied species, two morphologically distinct types of acrosomal vesicles were observed, a long structure, as observed in all known ants, and a pear‐shaped one, never before observed in ants. The nucleus is elongated and both condensed and loose chromatin are present. The flagellum has an axoneme, a centriolar adjunct, two mitochondrial derivatives and two accessory bodies. The centriolar, the mitochondrial derivatives and the accessory bodies are similar to observations in most ant species that have been studied. The axoneme presents an uncommon 9 + 9 + 1 microtubule arrangement and the central microtubule has 13 protofilaments. The acrosomal dimorphism and the different levels of chromatin organization are exclusive characteristics of Pseudomyrmex. Furthermore, the 9 + 9 + 1 microtubule arrangement is different from all Hymenoptera, as well as from most insects, which present a 9 + 9 + 2 arrangement. These new morphological characters that are specific to Pseudomyrmex, are valuable synapomorphies of the genus and can be used in taxonomic characterization of the Pseudomyrmecinae subfamily and in phylogenetic analyses in Formicidae family.     

Fertility interactions in Drosophila: Theoretical model and experimental tests

The results of 11 experiments with Drosophila species show that fertility is not a reducible property: the fertility of a mating pair cannot be predicted from the average fertility of the two genotypes involved. We propose a model of fertility selection that does not assume additivity (or multiplicativity) but assumes random mating and that the genotypic frequencies are in Hardy-Weinberg equilibrium. Numerical simulations show that removal of the assumption of Hardy-Weinberg frequencies does not significantly change the equilibrium frequencies predicted by the model.     

Time-resolved spectroscopy of the blue fluorescence of spinach leaves

When excited by ultraviolet radiation, leaves of a great number of species of higher plants exhibit emission of blue fluorescence, comparable in intensity to the red emission of chlorophyll. The fluorescence decay of the blue emission of spinach leaves recorded by single photon counting techniques is decomposed into exponential components and it is shown that at least three different components are present. The lifetime of the three components does not show significant variations with the excitation or emission wavelengths. The excitation and emission spectra of each component were determined. The nature of the chemical compounds which cause this emission is discussed in relation to these spectra.     

The fate of the fusarium mycotoxin zearalenone in maize cell suspension cultures

The fusarium mycotoxin zearalenone was transformed in cell suspension cultures of Zea mays giving α- and β-zearalenol and the β-D-glu cos ides of zearalenone and α- and β-zearalenol. The structure of zearalenone-4-β-D-glucopyranoside was determined by liquid — chromatography-mass spectrometry and specific hydrolysis with β-glucosidase. α- and β-zearalenol and their glucosides were identified by co chromatography using tic and HPLC and glucosidase — treatment Up to 50% of the mycotoxin added was bound to a non extractable or “bound” residue fraction. After treating this residue by a sequential cell wall fractionation procedure, zearalenone was found to be bound mainly to starch, hemicellulose, and lignin fractions.     

Repeated transfer of small RNA virus populations leading to balanced fitness with infrequent stochastic drift

The population dynamics of RNA viruses have an important influence on fitness variation and, in consequence, on the adaptative potential and virulence of this ubiquitous group of pathogens. Earlier work with vesicular stomatitis virus showed that large population transfers were reproducibly associated with fitness increases, whereas repeated transfers from plaque to plaque (genetic bottlenecks) lead to losses in fitness. We demonstrate here that repeated five-plaque to five-plaque passage series yield long-term fitness stability, except for occasional stochastic fitness jumps. Repeated five-plaque passages regularly alternating with two consecutive large population transmissions did not cause fitness losses, but did limit the size of fitness gains that would otherwise have occurred. These results underscore the profound effects of bottleneck transmissions in virus evolution.     

Gene transfer is a major factor in bacterial evolution

Lateral gene transfer in four strains of Salmonella enterica has been assessed using genomic subtraction. Strain LT2 (subspecies I serovar Typhimurium) chromosomal DNA was used as target and subtracted by three subspecies I strains of serovars Typhimurium (S21), Muenchen (S71), Typhi (M229), and a subspecies V strain (M321). Data from probing random cosmids of LT2 DNA with preparations of the residual LT2 DNA after subtraction were used to estimate the amounts of LT2 DNA not able to hybridize to strains S21, S71, M229, and M321 to be in the range of 84-106, 191-355, 305-629, and 778-1,286 kb, respectively. Several lines of evidence indicate that most of this DNA is from genes not present in strain M321 and not from genes that have diverged in sequence. The amounts correlate with the divergence of the four strains as revealed by multilocus enzyme electrophoresis and sequence variation of housekeeping genes. Sequence of 39 of the fragments from the M321 subtracted residual LT2 DNA revealed only six inserts of known gene function with evidence of both gain and loss of genes during the development of S. enterica clones. Sixteen of the 39 segments have 45% or lower G+C content, below the species average, but over half are within the normal range for the species. We conclude that even within a species, clones may differ by up to 20% of chromosomal DNA, indicating a major role for lateral transfer, and that on the basis of G+C content, a significant proportion of the DNA is from distantly related species.      

Identification of Endothelin Receptor Subtype (ETB) in Human Cerebral Cortex Using Subtype-Selective Ligands

Abstract: Specific endothelin (ET) binding sites were characterized in membranes prepared from human cerebral cortices using binding assay and cross-linking analysis. The presence of immunoreactive (IR) ET-1 was studied by radioimmunoassay. Saturation binding experiments revealed that the K _D and B _max for ¹²⁵I-ET-1 and ¹²⁵l-ET-3 to membranes from gray matter were 25 ± 6 pM and 115 ± 15 fmol/mg of protein and 24 ± 5 p M and 108 ± 13 fmol/mg of protein, respectively. Similar results were obtained for white matter. In the presence of 10 n M sarafotoxin-6c, which is selective for ET_B receptors, ¹²⁵I-ET-1 and ¹²⁵l-ET-3 binding was totally abolished. However, in the presence of 1 μ M BQ123, which is selective for ET_Areceptors, both bindings were not affected. These results suggest that the human cerebral cortex contains only ET_Breceptors. Cross-linking of ¹²⁵I-ET-1 and ¹²⁵l-ET-3 to membranes with disuccinimidyl suberate resulted in the labeling of two bands of 48 and 31 kDa. Concentrations of IR-ET-1 in the gray and white matter were 7.0 ± 3.2 and 2.5 ± 1.7 fmol/g wet weight, respectively. The demonstration of high-affinity ET_B receptors and the presence of IRET-1 suggest that the peptide may act as a neurotransmitter or neuromodulator in the human cerebral cortex.     

Characterization of Blue-Green Fluorescence in the Mesophyll of Sugar Beet (Beta vulgaris L.) Leaves Affected by Iron Deficiency

Protease C1, an enzyme from soybean (Glycine max [L.] Merrill cv Amsoy 71) seedling cotyledons, was previously determined to be the enzyme responsible for the initial degradation of the alpha' and alpha subunits, but not the beta subunit, of beta-conglycinin storage protein. The sizes of the proteolytic products generated by the action of protease C1 suggest that the cleavage sites on the alpha' and alpha subunits of beta-conglycinin may be located in their N-terminal domain, which is not found in the beta subunit of beta-conglycinin. To check this hypothesis, storage proteins from other plant species that are homologous to either the alpha'/alpha or the beta subunit of beta-conglycinin were tested as substrates. As expected, the convicilin from pea (Pisum sativum), a protein homologous to the alpha' and alpha subunits of beta-conglycinin, was digested by protease C1. The vicilins from pea as well as vicilins from adzuki bean (Vigna angularis), garden bean (Phaseolus vulgaris), black-eyed pea (Vigna unguiculata), and mung bean (Vigna radiata), storage proteins that are homologous to the beta subunit of soybean beta-conglycinin, were not degraded by protease C1. Degradation of soybean beta-conglycinin involves a sequential attack of the alpha subunit at multiple sites, culminating in the formation of a stable intermediate of 53.5 kD and a final product of 48.0 kD. The cleavage sites resulting in this formation of the intermediates and final product were determined by N-terminal analysis. These were compared to the known amino acid sequences of the three beta-conglycinin subunits. Results showed these two polypeptides to be generated by proteolysis of the alpha subunit at regions bearing long strings of acidic amino acid residues.