Local-scale species-energy relationships in fish assemblages of some forested streams of the Bolivian Amazon

Productivity (trophic energy) is one of the most important factors promoting variation in species richness. A variety of species-energy relationships have been reported, including monotonically positive, monotonically negative, or unimodal (i.e. hump-shaped). The exact form of the relationship seems to depend, among other things, on the spatial scale involved. However, the mechanisms behind these patterns are still largely unresolved, although many hypotheses have been suggested. Here we report a case of local-scale positive species-energy relationship. Using 14 local fish assemblages in tropical forested headwater streams (Bolivia), and after controlling for major local abiotic factors usually acting on assemblage richness and structure, we show that rising energy availability through leaf litter decomposition rates allows trophically specialized species to maintain viable populations and thereby to increase assemblage species richness. By deriving predictions from three popular mechanistic explanations, i.e. the 'increased population size', the 'consumer pressure', and the 'specialization' hypotheses, our data provide only equivocal support for the latter.     

Auxin Influx Carriers Control Vascular Patterning and Xylem Differentiation in Arabidopsis thaliana

Auxin is an essential hormone for plant growth and development. Auxin influx carriers AUX1/LAX transport auxin into the cell, while auxin efflux carriers PIN pump it out of the cell. It is well established that efflux carriers play an important role in the shoot vascular patterning, yet the contribution of influx carriers to the shoot vasculature remains unknown. Here, we combined theoretical and experimental approaches to decipher the role of auxin influx carriers in the patterning and differentiation of vascular tissues in the Arabidopsis inflorescence stem. Our theoretical analysis predicts that influx carriers facilitate periodic patterning and modulate the periodicity of auxin maxima. In agreement, we observed fewer and more spaced vascular bundles in quadruple mutants plants of the auxin influx carriers aux1lax1lax2lax3. Furthermore, we show AUX1/LAX carriers promote xylem differentiation in both the shoot and the root tissues. Influx carriers increase cytoplasmic auxin signaling, and thereby differentiation. In addition to this cytoplasmic role of auxin, our computational simulations propose a role for extracellular auxin as an inhibitor of xylem differentiation. Altogether, our study shows that auxin influx carriers AUX1/LAX regulate vascular patterning and differentiation in plants.     

A systems biology approach to dissect the contribution of brassinosteroid and auxin hormones to vascular patterning in the shoot of Arabidopsis thaliana

Systems biology can foster our understanding of hormonal regulation of plant vasculature. One such example is our recent study on the role of plant hormones brassinosteroids (BRs) and auxin in vascular patterning of Arabidopsis thaliana (Arabidopsis) shoots. By using a combined approach of mathematical modelling and molecular genetics, we have reported that auxin and BRs have complementary effects in the formation of the shoot vascular pattern. We proposed that auxin maxima, driven by auxin polar transport, position vascular bundles in the stem. BRs in turn modulate the number of vascular bundles, potentially by controlling cell division dynamics that enhance the number of provascular cells. Future interdisciplinary studies connecting vascular initiation at the shoot apex with the established vascular pattern in the basal part of the plant stem are now required to understand how and when the shoot vascular pattern emerges in the plant.Key words: Arabidopsis, vascular, auxin, brassinosteroids, mathematical model, computer simulationsThe plant vascular system is responsible for the long-distance transport of water, solutes and molecules throughout the plant, being essential for plant growth and development. It is formed by two different functional tissues: the xylem, which transports water from roots to aerial organs, and the phloem, through which nutrients and photosynthetic products and signaling molecules are transported.During embryogenesis, the vasculature is characterized as an undifferentiated procambial tissue in the innermost part of the plant embryo.¹ Later in development, the procambium (i.e., a group of pluripotent stem cells²) begins to divide and differentiate into xylem and phloem tissues through oriented cell divisions. In the shoot, procambium generates xylem tissue centripetally and phloem tissue centrifugally, driving the formation of collateral vascular bundles around it.^3,4 In the inflorescence stem of the model plant Arabidopsis, the radial pattern of the vasculature exhibits a periodic organization made by the alternation of vascular bundles and interfascicular fibers, which altogether form the vascular ring (Fig. 1A).Open in a separate windowFigure 1Vascular patterning in Arabidopsis shoot inflorescence stem. (A) Radial section of DR5::GUS expression at the base of the inflorescence stem in Arabidopsis Col-0 plants. (B) Computer simulation result for auxin concentration ([Auxin]) in arbitrary units (a.u.) along a ring of cells; x and y stand for spatial coordinates. Auxin is distributed in maxima which, according to the model hypothesis, position vascular bundles. (C) Longitudinal section of Arabidopsis Col-0 wild-type plant at the most apical zone, immediately below the shoot apical meristem. Arrows point to xylem strains coming from the lateral organs.Previous studies have documented the importance of plant hormones such as auxin and BRs in vascular cell differentiation and patterning.⁵ Defective polar auxin transport distorts shoot vascular patterning^6,7 and BR loss-of-function mutants exhibit few vascular bundles.^8,9 But how do these hormones control shoot vascular patterning? In order to answer this question, we used both quantitative measurements of vascular phenotypes and computational modeling.¹⁰     

Validation of liquid/liquid extraction method coupled with HPLC-UV for measurement of ribavirin plasma levels in HCV-positive patients

Measurement of ribavirin plasma levels in HCV-positive patients have been shown to be useful in order to optimise individual ribavirin exposure. Efficacy and toxicity of this drug are shown to be concentration-dependant. A simple HPLC-UV method was developed and validated, which has an easy liquid/liquid extraction, sensitive limit of detection, without any interference peaks, reproducible and linear over the range of clinical relevant concentrations. The assay warrants further evaluation as a tool for ribavirin therapeutic drug monitoring in HCV-positive patients.     

Genetic determinants of acute inflammation regulate Salmonella infection and modulate Slc11a1 gene (formerly Nramp1) effects in selected mouse lines

Two lines of mice selected to produce maximal (AIRmax) or minimal (AIRmin) acute inflammatory reactions (AIR) differ in their susceptibility to infection by Salmonella enterica serotype Typhimurium (S. Typhimurium). The LD(50) for AIRmax mice is 1000 times higher than that observed for AIRmin mice, and higher frequencies of Slc11a1 alleles (known to confer either resistance (R) or high susceptibility (S) to S. Typhimurium) were consistently found in AIRmax and AIRmin mouse lines, respectively. In order to evaluate the effect of the quantitative trait loci (QTL) segregated in AIRmax and AIRmin mice on Slc11a1 dependent susceptibility to S. Typhimurium, the R and S alleles were fixed in homozygosity in AIRmax and AIRmin backgrounds by genotype assisted breedings. These new lines were named AIRmax(RR), AIRmax(SS), AIRmin(RR), and AIRmin(SS). Acute inflammation of Slc11a1(RR) animals was more severe in comparison to their Slc11a1(SS) counterparts, implicating Slc11a1 (or other linked genes) in AIR regulation. The LD(50) of S. Typhimurium was 800-times higher for AIRmax(SS) than for AIRmin(SS), demonstrating that AIR QTL can act as modifiers of the Slc11a1(SS) susceptibility gene. Four microsatellite markers for S. Typhimurium susceptibility QTL described in other mouse lines showed specific allele fixation in AIRmax or AIRmin mice, suggesting that these chromosomal regions also segregate with inflammatory phenotypes.     

EMG spectral indices and muscle power fatigue during dynamic contractions

The purpose of this study was to examine acute exercise-induced changes on muscle power output and surface electromyography (sEMG) parameters (amplitude and spectral indices of muscle fatigue) during a dynamic fatiguing protocol. Fifteen trained subjects performed five sets consisting of 10 leg presses (10RM), with 2 min rest between sets. Surface electromyography was recorded from vastus medialis (VM) and lateralis (VL) and biceps femoris (BF) muscles. A number of EMG-based parameters were compared for estimation accuracy and sensitivity to detect peripheral muscle fatigue. These were: Mean Average Voltage, median spectral frequency, Dimitrov spectral index of muscle fatigue (FI_nsm5), as well as other parameters obtained from a time–frequency analysis (Choi–Williams distributions) such as mean and variance of the instantaneous frequency and frequency variance. The log FI_nsm5 as a single parameter predictor accounted for 37% of the performance variance of changes in muscle power and the log FI_nsm5 and MFM as a two factor combination predictor accounted for 44%. Peripheral impairments assessed by sEMG spectral index FI_nsm5 may be a relevant factor involved in the loss of power output after dynamic high-loading fatiguing task.     

Tethering naturally occurring peptide toxins for cell-autonomous modulation of ion channels and receptors in vivo

The physiologies of cells depend on electrochemical signals carried by ion channels and receptors. Venomous animals produce an enormous variety of peptide toxins with high affinity for specific ion channels and receptors. The mammalian prototoxin lynx1 shares with alpha-bungarotoxin the ability to bind and modulate nicotinic receptors (nAChRs); however, lynx1 is tethered to the membrane via a GPI anchor. We show here that several classes of neurotoxins, including bungarotoxins and cobratoxins, retain their selective antagonistic properties when tethered to the membrane. Targeted elimination of nAChR function in zebrafish can be achieved with tethered alpha-bungarotoxin, silencing synaptic transmission without perturbing synapse formation. These studies harness the pharmacological properties of peptide toxins for use in genetic experiments. When combined with specific methods of cell and temporal expression, the extension of this approach to hundreds of naturally occurring peptide toxins opens a new landscape for cell-autonomous regulation of cellular physiology in vivo.     

Micropropagation of Limonium cavanillesii Erben, a threatened statice, from inflorescence stems

Micropropagation of Limonium cavanillesii Erben, a threatened and endemic statice species from Valencia Community (Eastern Spain), was successfully achieved using inflorescence stem pieces as initial explants. Segments 20 mm long from basal parts of immature inflorescences and with axillary buds were cut, sterilised and established in vitro. Shoots obtained from indifferentiated buds were sectioned and then transferred to Murashige and Skoog (MS) medium with 2 mg l^–1 kinetin to provide a plant stock.Shoot multiplication was achieved on MS medium with different cytokinins. The best results for shoot formation were obtained with 2–5 mg l^–1kinetin, 5 mg l^–1 6---dimethylallylaminopurine or 0.1 mg l^–1 6-benzylaminopurine, without significant differences between them. High shoot rooting (80–85%) was obtained within four weeks with indolebutyric acid or indoleacetic acid (0.1 or 0.5 mg l^–1), and also on medium without plant growth regulators. Plant survival to hardened greenhouse conditions was 90% four weeks after plantlet removal from in vitro conditions.This protocol for micropropagation of Limonium cavanillesii is very useful for conservation purposes of endangered statice species, because by using inflorescence stem as initial material it is easier to establish aseptic cultures while preserving the mother plant.