Ultrastructure of Weddellomyces epicallopisma (Dothideales, Dacampiaceae, Ascomycota), especially of its ascospores]

An ultrastructural study of Weddellomyces epicallopisma (ascomata wall, asci, ascospores and vegetative hyphae), the first done on the family Dacampiaceae, confirms most of the observations made in light microscopy. Moreover it shows that ascospores are provided with an endospore (not visible in light microscope) and that the structure of the ascospore septum is more complex. The similarity of the wall structure between the ascospore and the hyphoid appendages, developed on the upper part of the ascoma, is emphasized.     

A simplified procedure for the concentration,desalting, and thin-layer chromatography of mevalonic acid from reaction mixtures used to assay 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity

A procedure has been described for the quantitative isolation of [¹⁴C]-mevalonic acid from reaction mixtures used for the assay of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. It consists of absorbing the reaction mixtures on Whatman No. 4 filter-paper supports and concentrating the radioactive substrate and the product within a 2-mm² area of the paper by two-dimensional elution with nonpolar solvents. This procedure simultaneously results in desalting of the reaction mixture, thus facilitating an excellent thin-layer chromatographic separation of mevalonolactone uncontaminated by the radioactive substrate. Among other advantages of the method are (a) quantitative extraction of mevalonolactone, thus avoiding the necessity of using an internal standard; (b) possibility of simultaneous processing of a large number of samples with the elution being carried out overnight without frequent supervision; (c) simplicity of the technical operations involved; and (d) inexpensiveness of the materials needed for analysis.     

Sur le mode de croissance de Nuia,algue incertae sedis

The authors recall some data concerning the distribution, the ecology and the taxonomy of Nuia and describe in detail its mode of growth, distinguished by 6 different growth-forms.     

Data limited assessment of selected North American anadromous charr stocks

Charr populations are particularly susceptible to change, either from the application of harvest or environmental conditions such as climate variation. As an alternative to conventional fishery analysis, we analyze the sustainability and viability of selected North American charr stocks using a number of approaches. We compare several methods for data limited situations to determine the allowable harvest of the Ekalluk River, Paliryauk River, Halovik River, Jayco Lake and Lauchlan River Arctic Charr including Cadima’s Maximum Sustainable Production Method, Hierarchical Bayesian Surplus Production Models, a Status Quo Total Allowable Harvest method, Long-term Average Catch methods and the Depletion-Corrected Average Catch method. Each method provided a similar outcome in terms of the relative importance of stocks to the fishery. The predicted sustainable harvest of larger stocks such as the Ekalluk and Jayco varied more according to the method applied than the other stocks studied. While not a replacement for more comprehensive fishery models these methods can be useful in data poor situations.     

Spatial partitioning of the soil water resource between grass and shrub components in a West African humid savanna

Most savanna water balance models assume water partitioning between grasses and shrubs in a two-layer hypothesis, but this hypothesis has not been tested for humid savanna environments. Spatial partitioning of soil water between grasses and shrubs was investigated in a West African humid savanna by comparing the isotopic composition (oxygen-18 and deuterium) of soil water and plant stem water during rainy and dry conditions. Both grass and shrub species acquire most of their water from the top soil layer during both rainy and dry periods. A shift of water uptake pattern towards deeper horizons was observed only at the end of the dry season after shrub defoliation. The mean depth of water uptake, as determined by the isotopic signature of stem water, was consistent with grass and shrub root profiles and with changes in soil water content profiles as surveyed by a neutron probe. This provides evidence for potentially strong competition between shrubs and grasses for soil water in these humid savannas. Limited nutrient availability may explain these competitive interactions. These results enhance our understanding of shrub-grass interactions, and will contribute to models of ecosystem functioning in humid savannas.     

Building of an experimental cline with Arabidopsis thaliana to estimate herbicide fitness cost

Various management strategies aim at maintaining pesticide resistance frequency under a threshold value by taking advantage of the benefit of the fitness penalty (the cost) expressed by the resistance allele outside the treated area or during the pesticide selection "off years." One method to estimate a fitness cost is to analyze the resistance allele frequency along transects across treated and untreated areas. On the basis of the shape of the cline, this method gives the relative contributions of both gene flow and the fitness difference between genotypes in the treated and untreated areas. Taking advantage of the properties of such migration-selection balance, an artificial cline was built up to optimize the conditions where the fitness cost of two herbicide-resistant mutants (acetolactate synthase and auxin-induced target genes) in the model species Arabidopsis thaliana could be more accurately measured. The analysis of the microevolutionary dynamics in these experimental populations indicated mean fitness costs of approximately 15 and 92% for the csr1-1 and axr2-1 resistances, respectively. In addition, negative frequency dependence for the fitness cost was also detected for the axr2-1 resistance. The advantages and disadvantages of the cline approach are discussed in regard to other methods of cost estimation. This comparison highlights the powerful ability of an experimental cline to measure low fitness costs and detect sensibility to frequency-dependent variations.     

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Non-contiguous finished genome sequence of Prevotella timonensis type strain 4401737T

Prevotella timonensis strain 4401737^T is a member of the genus Prevotella, which contains anaerobic Gram-negative bacteria. It was isolated from a human breast abscess. In this work, we describe a set of features of this organism, together with the complete genome sequence and annotation. The 3,169,464 bp long genome contains 2,746 protein-coding genes and 56 RNA genes, including 3 or 4 rRNA operons.     

Mesodern-inducing factors and mesodermal patterning

Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation.