Taking the pulse of snowmelt: in situ sensors reveal seasonal, event and diurnal patterns of nitrate and dissolved organic matter variability in an upland forest stream

Highly resolved time series data are useful to accurately identify the timing, rate, and magnitude of solute transport in streams during hydrologically dynamic periods such as snowmelt. We used in situ optical sensors for nitrate (NO₃ ^?) and chromophoric dissolved organic matter fluorescence (FDOM) to measure surface water concentrations at 30?min intervals over the snowmelt period (March 21–May 13, 2009) at a 40.5 hectare forested watershed at Sleepers River, Vermont. We also collected discrete samples for laboratory absorbance and fluorescence as well as δ¹⁸O–NO₃ ^? isotopes to help interpret the drivers of variable NO₃ ^? and FDOM concentrations measured in situ. In situ data revealed seasonal, event and diurnal patterns associated with hydrological and biogeochemical processes regulating stream NO₃ ^? and FDOM concentrations. An observed decrease in NO₃ ^? concentrations after peak snowmelt runoff and muted response to spring rainfall was consistent with the flushing of a limited supply of NO₃ ^? (mainly from nitrification) from source areas in surficial soils. Stream FDOM concentrations were coupled with flow throughout the study period, suggesting a strong hydrologic control on DOM concentrations in the stream. However, higher FDOM concentrations per unit streamflow after snowmelt likely reflected a greater hydraulic connectivity of the stream to leachable DOM sources in upland soils. We also observed diurnal NO₃ ^? variability of 1–2?μmol?l^?1 after snowpack ablation, presumably due to in-stream uptake prior to leafout. A comparison of NO₃ ^? and dissolved organic carbon yields (DOC, measured by FDOM proxy) calculated from weekly discrete samples and in situ data sub-sampled daily resulted in small to moderate differences over the entire study period (?4 to 1% for NO₃ ^? and ?3 to ?14% for DOC), but resulted in much larger differences for daily yields (?66 to +27% for NO₃ ^? and ?88 to +47% for DOC, respectively). Despite challenges inherent in in situ sensor deployments in harsh seasonal conditions, these data provide important insights into processes controlling NO₃ ^? and FDOM in streams, and will be critical for evaluating the effects of climate change on snowmelt delivery to downstream ecosystems.     

Use of an absorbable membrane to position biologically inductive materials in the periprosthetic space of cemented joints

A device is presented that positions ultrahigh molecular weight polyethylene (UHMWPE) debris against periprosthetic bone surfaces. This can facilitate the study of aseptic loosening associated with cemented joint prostheses by speeding the appearance of this debris within the periprosthetic space. The device, composed of a 100 microm thick bioabsorbable membrane impregnated with 1.4 x 10(9) sub-micron particles of UHMWPE debris, is positioned on the endosteum of the bone prior to the insertion of the cemented orthopedic implant. An in vitro pullout study and an in vivo canine pilot study were performed to investigate its potential to accelerate "time to aseptic loosening" of cemented prosthetic joints. Pullout studies characterized the influence of the membrane on initial implant fixation. The tensile stresses (mean+/-std.dev.) required to withdraw a prosthesis cemented into canine femurs with and without the membrane were 1.15+/-0.3 and 1.54+/-0.01 MPa, respectively; these findings were not significantly different (p > 0.4). The in vivo pilot study, involving five dogs, was performed to evaluate the efficacy of the debris to accelerate loosening in a canine cemented hip arthroplasty. Aseptic loosening and lameness occurred within 12 months, quicker than the 30 months reported in a retrospective clinical review of canine hip arthroplasty.     

Spiro-naphthyridinone piperidines as inhibitors of S. aureus and E. coli enoyl-ACP reductase (FabI)

Spiropiperidine naphthyridinone inhibitors of Staphylococcus aureus and Escherichia coli FabI have been prepared. Compounds 14a and 14c were identified as having sub-nanomolar E. coli FabI activity and are among the most potent FabI inhibitors yet described. The structural model of 14a bound to E. coli FabI is shown.     

<Emphasis Type="Italic">MlAG12</Emphasis>: a <Emphasis Type="Italic">Triticum timopheevii</Emphasis>-derived powdery mildew resistance gene in common wheat on chromosome 7AL

Wheat powdery mildew is an economically important disease in cool and humid environments. Powdery mildew causes yield losses as high as 48% through a reduction in tiller survival, kernels per head, and kernel size. Race-specific host resistance is the most consistent, environmentally friendly and, economical method of control. The wheat (Triticum aestivum L.) germplasm line NC06BGTAG12 possesses genetic resistance to powdery mildew introgressed from the AAGG tetraploid genome Triticum timopheevii subsp. armeniacum. Phenotypic evaluation of F₃ families derived from the cross NC06BGTAG12/‘Jagger’ and phenotypic evaluation of an F₂ population from the cross NC06BGTAG12/‘Saluda’ indicated that resistance to the ‘Yuma’ isolate of powdery mildew was controlled by a single dominant gene in NC06BGTAG12. Bulk segregant analysis (BSA) revealed simple sequence repeat (SSR) markers specific for chromosome 7AL segregating with the resistance gene. The SSR markers Xwmc273 and Xwmc346 mapped 8.3 cM distal and 6.6 cM proximal, respectively, in NC06BGTAG12/Jagger. The multiallelic Pm1 locus maps to this region of chromosome 7AL. No susceptible phenotypes were observed in an evaluation of 967 F₂ individuals in the cross NC06BGTAG12/‘Axminster’ (Pm1a) which indicated that the NC06BGTAG12 resistance gene was allelic or in close linkage with the Pm1 locus. A detached leaf test with ten differential powdery mildew isolates indicated the resistance in NC06BGTAG12 was different from all designated alleles at the Pm1 locus. Further linkage and allelism tests with five other temporarily designated genes in this very complex region will be required before giving a permanent designation to this gene. At this time the gene is given the temporary gene designation MlAG12.     

<Emphasis Type="Italic">Calycogonium bairdianum</Emphasis> (Melastomataceae: Miconieae), a new species from the Cordillera Central,Dominican Republic

Calycogonium bairdianum, a new species, is here described from the Cordillera Central of the Dominican Republic. It is compared to C. impressum, to which it is likely related. Although Calycogonium is not monophyletic, C. bairdianum and C. impressum may be related to other species in the genus that exhibit acarodomatia formed by hairs at the two major vein junctions on the leaf abaxial surface, a likely synapomorphy. Calycogonium bairdianum is distinguished from C. impressum by its relatively glabrous (vs. pubescent) and larger leaves (i.e., usually [2.9–]4.5–8.1 cm vs. 2.1–3.7 cm long) with veins that are plane to only slightly impressed adaxially (vs. more strongly impressed).     

Divalent cations increase lipid order in erythrocytes and susceptibility to secretory phospholipase A2

Elevated concentrations of intracellular calcium in erythrocytes increase membrane order and susceptibility to secretory phospholipase A2. We hypothesize that calcium aids the formation of domains of ordered lipids within erythrocyte membranes by interacting directly with the inner leaflet of the cell membrane. The interface of these domains with regions of more fluid lipids may create an environment with weakened neighbor-neighbor interactions that would facilitate phospholipid migration into the active site of bound secretory phospholipase A2. This hypothesis was investigated by determining the effects of seven other divalent ions on erythrocyte membrane properties. Changes in membrane order were assessed with steady-state fluorescence spectroscopy and two-photon microscopy with an environment-sensitive probe, laurdan. Each ion increased apparent membrane order in model membranes and in erythrocytes when introduced with an ionophore, suggesting that direct binding to the inner face of the membrane accounts for the effects of calcium on membrane fluidity. Furthermore, the degree to which ions affected membrane properties correlated with the ionic radius and electronegativity of the ions. Lastly, erythrocytes became more susceptible to enzyme hydrolysis in the presence of elevated intracellular levels of nickel and manganese, but not magnesium. These differences appeared related to the ability of the ions to induce a transition in erythrocyte shape.     

New species and records of Laboulbeniales from the subantarctic islands of New Zealand

Until now Rhachomyces kenodactyli Balazuc & W. Rossi has been the only species of Laboulbeniales known to occur on Coleoptera in the Bounty, Antipodes, Auckland, Campbell and Snares Islands, which lie 48° to 35° S. Four new species (Diphymyces depressus, Diphymyces leschenii, Laboulbenia subantarctica and Laboulbenia loxomeri) and five new records for the subantarctic (Cucujomyces phycophilus, Diphymyces penicillifer, Laboulbenia sp. 1, Rhachomyces sp. 1 and Teratomyces sp. 1) are reported, increasing the known number of taxa tenfold. An expanded geographic range for Rhachomyces kenodactyli is reported. A relatively high percentage (12%) of known beetle species in the subantarctic serve as hosts for Laboulbeniales. This host utilization rate is higher than that in tropical and north temperate regions. The high proportion of intertidal coleopteran taxa in the subantarctic fauna probably accounts for the greater number of host species utilized. Fungi on intertidal beetles (Omaliinae [Staphylinidae], Oopterus [Carabidae] and Kenodactylus audouini [Carabidae]) are known from many host individuals and collections, while those on terrestrial species are known from few, and in some cases, a single collection or host. The sporadic occurrence of some species encountered increases the likelihood that a few species of Laboulbeniales on Coleoptera probably remain undiscovered in the region.     

Mitochondrial DNA mutations as a fundamental mechanism in physiological declines associated with aging

The hypothesis that mitochondrial DNA damage accumulates and contributes to aging was proposed decades ago. Only recently have technological advancements, which facilitate microanalysis of single cells or portions of cells, revealed that mtDNA deletion mutations and, perhaps, single nucleotide mutations accumulate to physiologically relevant levels in the tissues of various species with age. Although a link between single nucleotide mutations and physiological consequences in aging tissue has not been established, the accumulation of deletion mutations in skeletal muscle fibres has been associated with sarcopenia. Different, and apparently random, deletion mutations are specific to individual fibres. However, the mtDNA deletion mutation within a phenotypically abnormal region of a fibre is the same, suggesting a selection, amplification and clonal expansion of the initial deletion mutation. mtDNA deletion mutations within a muscle fibre are associated with specific electron transport system abnormalities, muscle fibre atrophy and fibre breakage. These data point to a causal relationship between mitochondrial DNA mutations and the age-related loss of muscle mass.     

Impaired renal NaCl absorption in mice lacking the ROMK potassium channel,a model for type II Bartter's syndrome

ROMK is an apical K(+) channel expressed in the thick ascending limb of Henle (TALH) and throughout the distal nephron of the kidney. Null mutations in the ROMK gene cause type II Bartter's syndrome, in which abnormalities of electrolyte, acid-base, and fluid-volume homeostasis occur because of defective NaCl reabsorption in the TALH. To understand better the pathogenesis of type II Bartter's syndrome, we developed a mouse lacking ROMK and examined its phenotype. Young null mutants had hydronephrosis, were severely dehydrated, and approximately 95% died before 3 weeks of age. ROMK-deficient mice that survived beyond weaning grew to adulthood; however, they had metabolic acidosis, elevated blood concentrations of Na(+) and Cl(-), reduced blood pressure, polydipsia, polyuria, and poor urinary concentrating ability. Whole kidney glomerular filtration rate was sharply reduced, apparently as a result of hydronephrosis, and fractional excretion of electrolytes was elevated. Micropuncture analysis revealed that the single nephron glomerular filtration rate was relatively normal, absorption of NaCl in the TALH was reduced but not eliminated, and tubuloglomerular feedback was severely impaired. These data show that the loss of ROMK in the mouse causes perturbations of electrolyte, acid-base, and fluid-volume homeostasis, reduced absorption of NaCl in the TALH, and impaired tubuloglomerular feedback.