Effect of temperature on methane dynamics and evaluation of methane oxidation kinetics in shallow Arctic Alaskan lakes

Large uncertainties exist regarding the influence of ongoing climate change to microbially mediated methane cycling in arctic lakes. Specifically, the coupled response of methanogenesis (MG) and methane oxidation (Mox) to increased temperature is poorly understood. Therefore, the effect of temperature on rates of sediment MG and water column Mox in two shallow Arctic Alaskan lakes were evaluated in 2010. To understand the capacity of Mox to offset potential increases in dissolved methane concentrations, kinetics of water column Mox were also determined. Rates of MG responded positively to increased temperature with a greater influence exerted at higher incubation temperatures. Substrate-saturated Mox significantly increased with temperature and was controlled by substrate and temperature interactions. In contrast, substrate-limited Mox was not influenced by temperature and was controlled by substrate supply. Analysis of Mox kinetics pointed to a community of water column dwelling methane oxidizing bacteria that are capable of oxidizing dissolved methane concentrations far in excess of observed levels. Assuming no diffusion limitation, our results suggest that Mox will likely offset increased MG in response to elevated temperature regimes as a function of ongoing climate change.     

Substrate limitation of sediment methane flux,methane oxidation and use of stable isotopes for assessing methanogenesis pathways in a small arctic lake

Among predicted impacts of climate change in the Arctic are greater thaw depth and shifts in vegetation patterns and hydrology that are likely to increase organic carbon and nutrient loading to lakes. We measured substrate limitation of sediment methane (CH₄) flux, examined pathways of methanogenesis, and potential CH₄ oxidation using stable isotope labeled acetate in intact sediment cores from arctic lake GTH 112 (68°40′20″N, 149°14′57″W). We hypothesized that the acetoclastic pathway would dominate methanogenesis, reflecting dissolved organic carbon supply from the surrounding landscape, and that sediment CH₄ flux would be stimulated by addition of acetate. Experiments demonstrated acetate limitation of sediment CH₄ flux with short-term CH₄ flux response to availability of acetate, high rates of CH₄ oxidation, and strong dominance of the acetoclastic over the hydrogenotrophic methanogenic pathway. The experiments also indicated that isotopic fractionation effects during isotope enrichment experiments are large during methanogenesis and can alter the methanogenic pathways being investigated. Under oxic conditions, CH₄ oxidation at the sediment–water interface or in the water column is likely to account for much of diffusive CH₄ flux, but under anoxic hypolimnetic conditions and increased substrate availability, conditions that are likely to occur with climate change, sediment CH₄ flux will likely increase, with oxidation utilizing a smaller portion of sediment CH₄ production.     

Relationships between Fusarium population structure, soil nutrient status and disease incidence in field-grown asparagus

Fusarium species cause important diseases in many crops. Lack of knowledge on how Fusarium species and strains interact with their environment hampers growth management strategies to control root diseases. A field experiment involving asparagus as host plant and three phosphorus fertilization levels was designed to examine the seasonal changes and ecological relationships between Fusarium populations and their soil and plant environments. Fusarium taxa were identified and assessed using PCR-denaturing gradient electrophoresis of the EF1-alpha gene. Resulting profiles were analyzed with respect to 17 ecological parameters measured during the three main asparagus phenological phases across a growing season. Multivariate statistical analysis showed that Fusarium population structure was strongly influenced by soil P level while seasonal variation was less important. A significant relationship between Fusarium population composition and Fusarium crown and root rot incidence was also found in September. Canonical analysis further revealed significant relationships between Fusarium population structure, and plant manganese and iron contents, soil dehydrogenase activity and soil calcium concentration. If higher Fusarium crown and root rot incidence is related to the Fusarium community structure, strategies to reduce the incidence in asparagus plantations may be found through manipulation of the soil fertility.     

New roles for beta-arrestins in cell signaling: not just for seven-transmembrane receptors

beta-arrestins, originally discovered as molecules that bind to and desensitize the activated and phosphorylated form of the G protein-coupled beta2-adrenergic receptor (beta2-AR), have recently emerged as multifunctional adaptor/scaffold proteins that dynamically assemble a wide range of multiprotein complexes in response to stimulation of most seven-transmembrane receptors (7TMRs). These complexes mediate receptor signaling, trafficking, and degradation. Moreover, beta-arrestins are increasingly found to perform analogous functions for receptors from structurally diverse classes, including atypical 7TMRs such as frizzled and smoothened, the nicotinic cholinergic receptors, receptor tyrosine kinases, and cytokine receptors, thereby regulating a growing list of cellular processes such as chemotaxis, apoptosis, and metastasis.     

The emotional counting Stroop: a task for assessing emotional interference during brain imaging

The emotional counting Stroop (ecStroop) is an emotional variant of the counting Stroop. Both of these tasks require a motor response instead of a spoken response for the purpose of minimizing head movement during functional MRI (fMRI). During this task, subjects report, by button press, the number of words (1-4) that appear on a screen, regardless of word meaning. Neutral word-control trials contain common words (e.g., 'cabinet' written three times), while interference trials contain emotional words (e.g., 'murder' written three times). The degree to which this task represents a true 'Stroop' interference task, in the sense that emotional words will increase motor-response times compared with neutral words, depends upon the subjects of the study and the words that are presented. Much research on the emotional Stroop task demonstrates that interference effects are observed in psychopathological groups in response to words that are specific to their disorder, and in normal subjects when the words are related to current concerns endorsed by them. The ecStroop task described here will produce reaction time-interference effects that are comparable to the traditional color-naming emotional Stroop. This protocol can be completed in approximately 20 min per subject. The protocol described here employs neutral words and emotional words that include general-negative words, as well as words specific to combat-related trauma. However, this protocol is amenable to any emotional word lists.     

Analysis of flow cytometry DNA damage response protein activation kinetics after exposure to x rays and high-energy iron nuclei

We developed a mathematical method to analyze flow cytometry data to describe the kinetics of γ-H2AX and pATF2 phosphorylation in normal human fibroblast cells after exposure to various qualities of low-dose radiation. Previously reported flow cytometry kinetics for these DSB repair phospho-proteins revealed that distributions of intensity were highly skewed, severely limiting the detection of differences in the very low-dose range. Distributional analysis revealed significant differences between control and low-dose samples when distributions were compared using the Kolmogorov-Smirnov test. Differences in radiation quality were found in the distribution shapes and when a nonlinear model was used to relate dose and time to the decay of the mean ratio of phospho-protein intensities of irradiated samples to controls. We analyzed cell cycle phase- and radiation quality-dependent characteristic repair times and residual phospho-protein levels with these methods. Characteristic repair times for γ-H2AX were higher after exposure to iron nuclei compared to X rays in G(1) cells and in S/G(2) cells. The RBE in G(1) cells for iron nuclei relative to X rays for γ-H2AX was 2.1 ± 0.6 and 5.0 ± 3.5 at 2 and 24 h after irradiation, respectively. For pATF2, a saturation effect was observed with reduced expression at high doses, especially for iron nuclei, with much slower characteristic repair times (>7 h) compared to X rays. RBEs for pATF2 were 0.7 ± 0.1 and 1.7 ± 0.5 at 2 and 24 h, respectively. Significant differences in γ-H2AX and pATF2 levels when irradiated samples were compared to controls were noted even at the lowest dose analyzed (0.05 Gy). These results show that mathematical models can be applied to flow cytometry data to identify important and subtle differences after exposure to various qualities of low-dose radiation.     

WOOD ANATOMY OF THE AMERICAN FRANKENIAS (FRANKENIACEAE): SYSTEMATIC AND EVOLUTIONARY IMPLICATIONS

Results of a comparative wood anatomical survey of the American frankenias are presented. The eleven species examined are woody perennials occurring almost exclusively in arid and semiarid regions and on saline and gypseous soils. The secondary xylem of all species is highly specialized and is characterized by libriform fibers, vessel elements with simple perforation plates, and the absence of rays. Axial elements of all species are quite small. A number of unusual features, e.g., anomalous secondary growth and formation of interxylary cork, were observed in some species. Nonfibrous woods have evolved independently in two species of reduced stature and contrast markedly with the highly fibrous woods of most species. Woods of the American frankenias are compared with those of the Tamaricaceae. The systematic and evolutionary implications of interspecific variation in both qualitative and quantitative features are discussed. There is a general tendency for dimensions of the axial wood elements to be positively associated and to decrease with decreasing plant height. In general, differences in wood anatomy more strongly reflect differences in plant growth form and size than phylogeny.