Winter food habits of the pine marten in Colorado

Eighteen pine marten ( Martes americana ) stomachs and 29 intestinal tracts, collected between October 1983 and March 1984 from northern Colorado, were examined for food items. Voles ( Microtus spp.) occurred most frequently, followed by shrews ( Sorex spp.), insects, and vegetative matter.     

Cattail decline at Farmington Bay Waterfowl Management Area

For the last seven years, 1969 to 1976, a steady decline of cattails ( Typha latifolia L.) has been observed at Farmington Bay Waterfowl Management Area, Davis County, Utah. Several parameters of Farmington Bay's environment that could cause or enhance a decline of the marshland vegetation were studied. These parameters included temperature, pH, phenols, oil and grease, heavy metals, fungus pathogens, and salt water intrusion from the Great Salt Lake. Elevated soluble salt concentrations were found to be responsible for the decline. Cattails are weakened or killed when they are exposed to soluble salt concentrations greater than 5.0 gm/liter, and there is a significant (1 percent level) negative correlation ( - 0.68) between soluble salt concentration and cattail height. Symptoms of elevated salt concentrations include stunted growth, leaf tip necrosis (burning), and occasional browning of an entire cattail clone. Furthermore, those salt concentrations that cause physiological stress in cattails also facilitate the growth of a decomposition fungus, Chaetophoma confluens. This fungus causes a rot consisting of irregularly scattered lesions on the surface of the rhizomes and was consistently isolated from rhizomes of declining plants.       

Controls on radial growth of mountain big sagebrush and implications for climate change

Mountain big sagebrush ( Artemisia tridentata Nutt. ssp. vaseyana ) covers large areas in arid regions of western North America. Climate-change models predict a decrease in the range of sagebrush, but few studies have examined details of predicted changes on sagebrush growth and the potential impacts of these changes on the community. We analyzed effects of temperature, precipitation, and snow depth on sagebrush annual ring width for 1969 to 2007 in the Gunnison Basin of Colorado. Temperature at all times of year except winter had negative correlations with ring widths; summer temperature had the strongest negative relationship. Ring widths correlated positively with precipitation in various seasons except summer; winter precipitation had the strongest relationship with growth. Maximum snow depth also correlated positively and strongly with ring width. Multiple regressions showed that summer temperature and either winter precipitation or maximum snow depth, which recharges deeper soil horizons, are both important in controlling growth. Overall, water stress and perhaps especially maximum snow depth appear to limit growth of this species. With predicted increases in temperature and probable reduced snow depth, sagebrush growth rates are likely to decrease. If so, sagebrush populations and cover may decline, which may have substantial effects on community composition and carbon balance.     

银河系中的球状星团

球状星团是大量恒星的紧密集合,同时也是银河系中最年老的恒星系统,并在银河系形成和演化的研究中也扮演着重要的角色。但是,正如在本期的杂志     

Adriamycin-induced chromosome damage: Elevated frequencies of isochromatid aberrations in G2 and S phases

Summary Analysis of chromosomes from cells treated with adriamycin during G₂ and S phases showed a high frequency of isochromatid-type of breaks, in addition to the expected chromatid breaks. These are interpreted as independent breaks on sister chromatids because of preferential effects of the drug in specific chromosome regions. The break points are likely to be different, but morphologically such breaks would be indistinguishable from isochromatid or chromosome breaks.Supported in part by NO1-CM-53773 Division of Cancer Treatment NCI, Bethesda, Maryland, and by Research Grant No. VC-21 from American Cancer Society.     

Absorption of glycine and proline from the small intestine of rats infected withEimeria nieschulzi

Summary The absorption of glycine and proline through the jejunum and ileum of rats with anEimeria nieschulzi infection was impaired when the amino acids were presented to the mucosal surface as either a mixture or the dipeptide, glycyl-proline.     

The Srs2 helicase prevents recombination by disrupting Rad51 nucleoprotein filaments

Homologous recombination is a ubiquitous process with key functions in meiotic and vegetative cells for the repair of DNA breaks. It is initiated by the formation of single-stranded DNA on which recombination proteins bind to form a nucleoprotein filament that is active in searching for homology, in the formation of joint molecules and in the exchange of DNA strands. This process contributes to genome stability but it is also potentially dangerous to cells if intermediates are formed that cannot be processed normally and thus are toxic or generate genomic rearrangements. Cells must therefore have developed strategies to survey recombination and to prevent the occurrence of such deleterious events. In Saccharomyces cerevisiae, genetic data have shown that the Srs2 helicase negatively modulates recombination, and later experiments suggested that it reverses intermediate recombination structures. Here we show that DNA strand exchange mediated in vitro by Rad51 is inhibited by Srs2, and that Srs2 disrupts Rad51 filaments formed on single-stranded DNA. These data provide an explanation for the anti-recombinogenic role of Srs2 in vivo and highlight a previously unknown mechanism for recombination control.