Temperature and precipitation controls over leaf‐ and ecosystem‐level CO2 flux along a woody plant encroachment gradient

Conversion of grasslands to woodlands may alter the sensitivity of CO₂ exchange of individual plants and entire ecosystems to air temperature and precipitation. We combined leaf‐level gas exchange and ecosystem‐level eddy covariance measurements to quantify the effects of plant temperature sensitivity and ecosystem temperature responses within a grassland and mesquite woodland across seasonal precipitation periods. In so doing, we were able to estimate the role of moisture availability on ecosystem temperature sensitivity under large‐scale vegetative shifts. Optimum temperatures (T_opt) for net photosynthetic assimilation (A) and net ecosystem productivity (NEP) were estimated from a function fitted to A and NEP plotted against air temperature. The convexities of these temperature responses were quantified by the range of temperatures over which a leaf or an ecosystem assimilated 50% of maximum NEP (Ω₅₀). Under dry pre‐ and postmonsoon conditions, leaf‐level Ω₅₀ in C₃ shrubs were two‐to‐three times that of C₄ grasses, but under moist monsoon conditions, leaf‐level Ω₅₀ was similar between growth forms. At the ecosystems‐scale, grassland NEP was more sensitive to precipitation, as evidenced by a 104% increase in maximum NEP at monsoon onset, compared to a 57% increase in the woodland. Also, woodland NEP was greater across all temperatures experienced by both ecosystems in all seasons. By maintaining physiological function across a wider temperature range during water‐limited periods, woody plants assimilated larger amounts of carbon. This higher carbon‐assimilation capacity may have significant implications for ecosystem responses to projected climate change scenarios of higher temperatures and more variable precipitation, particularly as semiarid regions experience conversions from C₄ grasses to C₃ shrubs. As regional carbon models, CLM 4.0, are now able to incorporate functional type and photosynthetic pathway differences, this work highlights the need for a better integration of the interactive effects of growth form/functional type and photosynthetic pathway on water resource acquisition and temperature sensitivity.     

Multivariate regulation of soil CO2 and N2O pulse emissions from agricultural soils

Climate and land‐use models project increasing occurrence of high temperature and water deficit in both agricultural production systems and terrestrial ecosystems. Episodic soil wetting and subsequent drying may increase the occurrence and magnitude of pulsed biogeochemical activity, affecting carbon (C) and nitrogen (N) cycles and influencing greenhouse gas (GHG) emissions. In this study, we provide the first data to explore the responses of carbon dioxide (CO₂) and nitrous oxide (N₂O) fluxes to (i) temperature, (ii) soil water content as percent water holding capacity (%WHC), (iii) substrate availability throughout, and (iv) multiple soil drying and rewetting (DW) events. Each of these factors and their interactions exerted effects on GHG emissions over a range of four (CO₂) and six (N₂O) orders of magnitude. Maximal CO₂ and N₂O fluxes were observed in environments combining intermediate %WHC, elevated temperature, and sufficient substrate availability. Amendments of C and N and their interactions significantly affected CO₂ and N₂O fluxes and altered their temperature sensitivities (Q₁₀) over successive DW cycles. C amendments significantly enhanced CO₂ flux, reduced N₂O flux, and decreased the Q₁₀ of both. N amendments had no effect on CO₂ flux and increased N₂O flux, while significantly depressing the Q₁₀ for CO₂, and having no effect on the Q₁₀ for N₂O. The dynamics across DW cycles could be attributed to changes in soil microbial communities as the different responses to wetting events in specific group of microorganisms, to the altered substrate availabilities, or to both. The complex interactions among parameters influencing trace gas fluxes should be incorporated into next generation earth system models to improve estimation of GHG emissions.     

Correlating Function and Imaging Measures of the Medial Longitudinal Fasciculus

Objective

To test the validity of diffusion tensor imaging (DTI) measures of tissue injury by examining such measures in a white matter structure with well-defined function, the medial longitudinal fasciculus (MLF). Injury to the MLF underlies internuclear ophthalmoparesis (INO).

Methods

40 MS patients with chronic INO and 15 healthy controls were examined under an IRB-approved protocol. Tissue integrity of the MLF was characterized by DTI parameters: longitudinal diffusivity (LD), transverse diffusivity (TD), mean diffusivity (MD) and fractional anisotropy (FA). Severity of INO was quantified by infrared oculography to measure versional disconjugacy index (VDI).

Results

LD was significantly lower in patients than in controls in the medulla-pons region of the MLF (p < 0.03). FA was also lower in patients in the same region (p < 0.0004). LD of the medulla-pons region correlated with VDI (R = -0.28, p < 0.05) as did FA in the midbrain section (R = 0.31, p < 0.02).

Conclusions

This study demonstrates that DTI measures of brain tissue injury can detect injury to a functionally relevant white matter pathway, and that such measures correlate with clinically accepted evaluation indices for INO. The results validate DTI as a useful imaging measure of tissue integrity.     

Two-dimensional crystallization of human vitamin K-dependent gamma-glutamyl carboxylase

Planar-tubular two-dimensional (2D) crystals of human vitamin K-dependent gamma-glutamyl carboxylase grow in the presence of dimyristoyl phosphatidylcholine (DMPC). Surprisingly, these crystals form below the phase transition temperature of DMPC and at the unusually low molar lipid-to-protein (LPR) ratio of 1, while 2D crystals are conventionally grown above the phase transition temperature of the reconstituting lipid and significantly higher LPRs. The crystals are up to 0.75 microm in the shorter dimension of the planar tubes and at least 1 microm in length. Due to the planar-tubular nature of the crystals, two lattices are present. These are rotated by nearly 90 degrees in respect to each other. The ordered arrays exhibit p12(1) plane group symmetry with unit cell dimensions of a=83.7 A, b=76.6 A, gamma=91 degrees. Projection maps calculated from images of negatively stained and electron cryo-microscopy samples reveal the human vitamin K-dependent gamma-glutamyl carboxylase to be a monomer.     

A computational study on the influence of catheter-delivered intravascular probes on blood flow in a coronary artery model

Catheter-delivered intravascular probes are widely used in clinical practice to measure coronary arterial velocity and pressure, but the artefactual effect of the probe on the variables being measured is not well characterised. A coronary artery was simulated with a 180 degrees curved tube 3mm in diameter and the effect of catheters of different diameters was modelled numerically under pulsatile flow conditions. The presence of a catheter increased pressure by 1.3-4.3 mmHg depending on its diameter, and reduced velocity-pressure phase-lag. For an ultrasound sample volume 5mm downstream from the probe tip, the underestimation in velocity measurement attributed to catheter blockage is approximately 15-21% for an average inlet velocity of 0.1m/s. The velocity measurement error is lower at higher mean flow velocity. Accuracy of clinical velocity measurements could be improved by moving the sample volume farther downstream from the probe tip, because the centrifugal pressure gradient intrinsic to the curvature promotes re-development of flow.     

HIV-1 Nef associates with p22-phox, a component of the NADPH oxidase protein complex

Altered neutrophil function may contribute to the development of AIDS during the course of HIV infection. It has been described that Nef, a regulatory protein from HIV, can modulate superoxide production in other cells, therefore altered superoxide production in neutrophils from HIV infected patients, could be secondary to a direct effect of Nef on components of the NADPH oxidase complex. In this work, we describe that Nef, was capable of increasing superoxide production in human neutrophils. Furthermore, a specific association between Nef and p22-phox, a membrane component of the NADPH oxidase complex, was found. We propose that this association may reflect a capability of Nef to modulate by direct association, the enzymatic complex responsible for one of the most efficient innate defense mechanisms in phagocytes, contributing to the pathogenesis of the disease.     

Haploinsufficiency of TAB2 Causes Congenital Heart Defects in Humans

Congenital heart defects (CHDs) are the most common major developmental anomalies and the most frequent cause for perinatal mortality, but their etiology remains often obscure. We identified a locus for CHDs on 6q24-q25. Genotype-phenotype correlations in 12 patients carrying a chromosomal deletion on 6q delineated a critical 850 kb region on 6q25.1 harboring five genes. Bioinformatics prioritization of candidate genes in this locus for a role in CHDs identified the TGF-β-activated kinase 1/MAP3K7 binding protein 2 gene (TAB2) as the top-ranking candidate gene. A role for this candidate gene in cardiac development was further supported by its conserved expression in the developing human and zebrafish heart. Moreover, a critical, dosage-sensitive role during development was demonstrated by the cardiac defects observed upon titrated knockdown of tab2 expression in zebrafish embryos. To definitively confirm the role of this candidate gene in CHDs, we performed mutation analysis of TAB2 in 402 patients with a CHD, which revealed two evolutionarily conserved missense mutations. Finally, a balanced translocation was identified, cosegregating with familial CHD. Mapping of the breakpoints demonstrated that this translocation disrupts TAB2. Taken together, these data clearly demonstrate a role for TAB2 in human cardiac development.     

Effects of copper on branchial ionoregulation in the rainbow trout,Salmo gairdneri Richardson

Summary Hard- and softwater acclimated adult rainbow trout were statically exposed to copper (12.5, 25, 50, 100, and 200 ppb) for two, 12 h periods at neutral and pH 5.0. Unidirectional Na⁺, and Cl⁻, and net Na⁺, Cl⁻, K⁺, and ammonia fluxes were monitored as a measure of branchial ionoregulatory disturbance. Copper concentrations as low as 12.5 ppb led to measurable ion losses. Net Na⁺, Cl⁻, and K⁺ losses were concentration dependent and unaffected by prior acclimation to either hard- or softwater at both neutral pH and pH 5. From 12.5 to 50 ppb net NaCl losses arose primarily as a result of the inhibition ofJ _in, and at higher concentrations,J _out was also stimulated. In softwater,J _in was more resistant to inhibition than in hardwater. However, in hardwater,J _out recovered to normal levels during the second 12 h period, but no such recovery was found in softwater. Plasma NaCl was inversely correlated with [copper], while plasma glucose and ammonia increased with [copper]. At pH 5.0 and [copper] from 12.5 to 50 ppb, H⁺ contributed significantly to the total ion loss, while at 100 and 200 ppb, ion losses were no greater at pH 5.0 than at neutral pH. In no case were the effects of copper and H⁺ strictly additive.     

Functional diversity within the rudimentary locus of Drosophila melanogaster

Summary The rudimentary locus of Drosophila melanogaster is shown to be at least bifunctional. Mutants in different regions of the locus have either no CPSase or no ATCase activity; some mutants lack both activities. The results are discussed in correlation with the complementation and genetic map of the locus.Supported by National Research Council of Canada, grant A-1764 and National Cancer Institute of Canada, grant 6051 to D. T. Suzuki.Researcher, Centre National de la Recherche Scientifique, France and recipient of European Molecular Biology Organization Fellowship.