Snow depth manipulation and its influence on soil frost and water dynamics in a northern hardwood forest

Climate change will likelyresult in warmer winter temperatures leading toless snowfall in temperate forests. Thesechanges may lead to increases in soil freezingbecause of lack of an insulating snow cover andchanges in soil water dynamics during theimportant snowmelt period. In this study, wemanipulated snow depth by removing snow for twowinters, simulating the late development of thesnowpack as may occur with global warming, toexplore the relationships between snow depth,soil freezing, soil moisture, and infiltration.We established four sites, each with two pairedplots, at the Hubbard Brook Experimental Forest(HBEF) in New Hampshire, U.S.A. and instrumentedall eight plots with soil and snow thermistors,frost tubes, soil moisture probes, and soillysimeters. For two winters, we removed snowfrom the designated treatment plots untilFebruary. Snow in the reference plots wasundisturbed. The treatment winters (1997/1998 and1998/1999) were relatively mild, withtemperatures above the seasonal norm and snowdepths below average. Results show the treatedplots accumulated significantly less snow andhad more extensive soil frost than referenceplots. Snow depth was a strong regulator ofsoil temperature and frost depth at all sites.Soil moisture measured by time domainreflectometry probes and leaching volumescollected in lysimeters were lower in thetreatment plots in March and April compared tothe rest of the year. The ratio of leachatevolumes collected in the treatment plots tothat in the reference plots decreased as thesnow ablation seasons progressed. Our data showthat even mild winters with low snowfall,simulated by snow removal, will result inincreased soil freezing in the forests at theHBEF. Our results suggest that a climate shifttoward less snowfall or a shorter duration ofsnow on the ground will produce increases insoil freezing in northern hardwood forests.Increases in soil freezing will haveimplications for changes in soil biogeochemicalprocesses.     

Oligonucleotide biological activity: Relationship to the cell cycle and nuclear transport

Previous studies suggest that oligodeoxynucleotide (ODN) cellular uptake is cell cycle-dependent which may have important implications in cancer cell targeting. To further our understanding of ODN transport and activity, this study examines the relationships between the cell cycle, ODN cellular uptake, intracellular transport, and activity. An antisense c-myc ODN 21-mer was used to study ODN cellular uptake in Rauscher erythroleukemia cells synchronized by either chemical methods or flow cytometry. ODN uptake was examined using subcellular fractionation and confocal fluorescence microscopy. Western blot analysis was used to measure ODN-mediated decreases in c-myc protein levels. Intracellular ODN distribution and extent of uptake was influenced by the phase of the cell cycle, but the mechanism of uptake was not. The relative activity of the antisense ODN was positively correlated to ODN distribution to the cytosol, but negatively correlated to total cellular uptake. Although ODN total cellular uptake is positively influenced by the cell cycle, retention of the ODN in the cytosol (presumably extra-vesicularly) appeared to be relevant in determining the activity of an antisense ODN. Novel methods to target cytosol-acting drugs to the cytoplasm may therefore be warrented.     

Wall-associated processing of extracellular enzymes of Staphylococcus simulans biovar staphylolyticus

Staphylococcus simulans biovar staphylolyticus produces a staphylolytic glycylglycine endopeptidase (lysostaphin) and a micrococcolytic endo-β-N-acetylglucosaminidase (hexosaminidase) as proenzymes that are proteolytically processed through multiple intermediates to their mature forms by an extracellular sulfhydryl protease. Analysis of protease production by immunoblots using antiserum prepared against purified protease and by renaturing activity gels using gelatin as the substrate has revealed that the lysostaphin-processing protease also is produced as a proenzyme, which appears to be autocatalytically processed. Very little proprotease could be detected in supernatants from cultures of S. simulans biovar staphylolyticus, which suggested that the protein was being processed before it was released to the culture medium. Analysis of wall-associated proteins revealed that processing of proprotease occurred primarily in the cell wall. Furthermore, processing of prolysostaphin and prohexosaminidase also occurred in the cell wall matrix.     

Drosophila Wee1 interacts with members of the gammaTURC and is required for proper mitotic-spindle morphogenesis and positioning

BACKGROUND: Wee1 kinases delay entry into mitosis by phosphorylating and inactivating cyclin-dependent kinase 1 (Cdk1). Loss of this activity in many systems, including Drosophila, leads to premature mitotic entry. RESULTS: We report here that Drosophila Wee1 (dwee1) mutant embryos show mitotic-spindle defects that include ectopic foci of microtubule organization, formation of multipolar spindles from adjacent centrosome pairs, and promiscuous interactions between neighboring spindles. Furthermore, centrosomes are displaced from the embryo cortex in dwee1 mutants. These defects are not observed to the same extent in embryos in which nuclei also enter mitosis prematurely as a result of a lack of checkpoint control or in embryos with elevated Cdk1 activity. dWee1 physically interacts with members of the gamma-tubulin ring complex (gammaTuRC), and gamma-tubulin is phosphorylated in a dwee1-dependent manner in embryo extracts. CONCLUSIONS: Some of the abnormalities in dwee1 mutant embryos cannot be explained by premature entry into mitosis or bulk elevation of Cdk1 activity. Instead, dWee1 is also required for phosphorylation of gamma-tubulin, centrosome positioning, and mitotic-spindle integrity. We propose a model to account for these requirements.     

Expanding the genetic code of Drosophila melanogaster

Genetic code expansion for unnatural amino acid mutagenesis has, until recently, been limited to cell culture. We demonstrate the site-specific incorporation of unnatural amino acids into proteins in Drosophila melanogaster at different developmental stages, in specific tissues and in a subset of cells within a tissue. This approach provides a foundation for probing and controlling processes in this established metazoan model organism with a new level of molecular precision.     

Rangewide landscape genetics of an endemic Pacific northwestern salamander

A species' genetic structure often varies in response to ecological and landscape processes that differ throughout the species' geographic range, yet landscape genetics studies are rarely spatially replicated. The Cope's giant salamander (Dicamptodon copei) is a neotenic, dispersal‐limited amphibian with a restricted geographic range in the Pacific northwestern USA. We investigated which landscape factors affect D. copei gene flow in three regions spanning the species' range, which vary in climate, landcover and degree of anthropogenic disturbance. Least cost paths and Circuitscape resistance analyses revealed that gene flow patterns vary across the species' range, with unique combinations of landscape variables affecting gene flow in different regions. Populations in the northern coastal portions of the range had relatively high gene flow, largely facilitated by stream and river networks. Near the southeastern edge of the species' range, gene flow was more restricted overall, with relatively less facilitation by streams and more limitation by heat load index and fragmented forest cover. These results suggested that the landscape is more difficult for individuals to disperse through at the southeastern edge of the species' range, with terrestrial habitat desiccation factors becoming more limiting to gene flow. We suggest that caution be used when attempting to extrapolate landscape genetic models and conservation measures from one portion of a species' range to another.     

Mechanistic studies of the yeast polyamine oxidase Fms1: kinetic mechanism, substrate specificity, and pH dependence

The flavoprotein oxidase Fms1 from Saccharomyces cerevisiae catalyzes the oxidation of spermine and N(1)-acetylspermine to yield spermidine and 3-aminopropanal or N-acetyl-3-aminopropanal. The kinetic mechanism of the enzyme has been determined with both substrates. The initial velocity patterns are ping-pong, consistent with reduction being kinetically irreversible. Reduction of Fms1 by either substrate is biphasic. The rate constant for the rapid phase varies with the substrate concentration, with limiting rates for reduction of the enzyme of 126 and 1410 s(-1) and apparent K(d) values of 24.3 and 484 μM for spermine and N(1)-acetylspermine, respectively. The rapid phase is followed by a concentration-independent phase that is slower than turnover. The reaction of the reduced enzyme with oxygen is monophasic, with a rate constant of 402 mM(-1) s(-1) with spermine at 25 °C and 204 mM(-1) s(-1) with N(1)-acetylspermine at 4 °C and pH 9.0. This step is followed by rate-limiting product dissociation. The k(cat)/K(amine)-pH profiles are bell-shaped, with an average pK(a) value of 9.3 with spermine and pK(a) values of 8.3 and 9.6 with N(1)-acetylspermine. Both profiles are consistent with the active forms of substrates having two charged nitrogens. The pH profiles for the rate constant for flavin reduction show pK(a) values of 8.3 and 7.2 for spermine and N(1)-acetylspermine, respectively, for groups that must be unprotonated; these pK(a) values are assigned to the substrate N4. The k(cat)/K(O(2))-pH profiles show pK(a) values of 7.5 for spermine and 6.8 for N(1)-acetylspermine. With both substrates, the k(cat) value decreases when a single residue is protonated.