Airborne and belowground phytotoxicity of invasive Ageratina adenophora on native species in Nepal

Plant Ecology - Volatile compounds from leaf litter of invasive alien Ageratina adenophora are known to inhibit growth of native species in sub-tropical Asia, but there is not...     

Autoradiographic imaging of altered synaptic alphabetagamma2 and extrasynaptic alphabeta GABAA receptors in a genetic mouse model of anxiety

To image the possible alterations in brain regional GABAA receptor subtype properties in a genetic animal model of human anxiety, mice heterozygous for the deletion of GABAA receptor gamma2 subunit (gamma2+/-) were studied using ligand autoradiographic assays on brain cryostat sections. The [35S]TBPS binding assay was designed to reveal impaired GABA and channel site coupling shown to be more prominent in recombinant alpha1/6beta3 than in alpha1/2beta3gamma2 or beta2 subunit-containing GABAA receptors expressed in HEK 293 cells. Increased GABA-insensitive [35 S]TBPS binding in the gamma2+/- mouse brains was evident in the cerebral cortex and in subcortical regions, the alterations being regionally similar to the loss of gamma2 subnunit-dependent benzodiazepine (BZ) sites as revealed by [3H]Ro 15-4513 autoradiography. As the gamma2 subunit protein is needed for synaptic clustering of GABAA receptors, these results indicate that the extrasynaptic alphabeta3 receptors can be visualized in vitro as atypical GABA-insensitive [35S]TBPS binding sites. The results suggest that GABAAergic synaptic inhibition is widely decreased in the brains of anxiety-prone gamma2+/- mice, while extrasynaptic GABAA receptors are increased. These autoradiographic imaging findings further demonstrate the need to develop GABAA receptor subtype-selective in vivo ligands to aid in assessing the contributions of various subcellular receptor populations in anxious and other patient groups.     

Modelling the effect of autotoxicity on density-dependent phytotoxicity

An established method to separate resource competition from chemical interference is cultivation of monospecific, even-aged stands. The stands grow at several densities and they are exposed to homogenously spread toxins. Hence, the dose received by individual plants is inversely related to stand density. This results in distinguishable alterations in dose-response slopes. The method is often recommended in ecological studies of allelopathy. However, many plant species are known to release autotoxic compounds. Often, the probability of autotoxicity increases as sowing density increases. Despite this, the possibility of autotoxicity is ignored when experiments including monospecific stands are designed and when their results are evaluated. In this paper, I model mathematically how autotoxicity changes the outcome of dose-response slopes as different densities of monospecific stands are grown on homogenously phytotoxic substrata. Several ecologically reasonable relations between plant density and autotoxin exposure are considered over a range of parameter values, and similarities between different relations are searched for. The models indicate that autotoxicity affects the outcome of density-dependent dose-response experiments. Autotoxicity seems to abolish the effects of other phytochemicals in certain cases, while it may augment them in other cases. Autotoxicity may alter the outcome of tests using the method of monospecific stands even if the dose of autotoxic compounds per plant is a fraction of the dose of non-autotoxic phytochemicals with similar allelopathic potential. Data from the literature support these conclusions. A faulty null hypothesis may be accepted if the autotoxic potential of a test species is overlooked in density-response experiments. On the contrary, if test species are known to be non-autotoxic, the method of monospecific stands does not need fine-tuning. The results also suggest that the possibility of autotoxicity should be investigated in many density-response bioassays that are made with even-aged plants, and that measure plant growth or germination.     

Associative clustering for exploring dependencies between functional genomics data sets

High-throughput genomic measurements, interpreted as cooccurring data samples from multiple sources, open up a fresh problem for machine learning: What is in common in the different data sets, that is, what kind of statistical dependencies are there between the paired samples from the different sets? We introduce a clustering algorithm for exploring the dependencies. Samples within each data set are grouped such that the dependencies between groups of different sets capture as much of pairwise dependencies between the samples as possible. We formalize this problem in a novel probabilistic way, as optimization of a Bayes factor. The method is applied to reveal commonalities and exceptions in gene expression between organisms and to suggest regulatory interactions in the form of dependencies between gene expression profiles and regulator binding patterns.     

Sexual reproduction advances autumn leaf colours in mountain birch (Betula pubescens ssp. czerepanovii)

Autumnal change in leaf colour of deciduous trees is one of the most fascinating displays in nature. Current theories suggest that autumn leaf colours are adaptations to environmental stress. Here I report that the number of ripening female catkins altered timing of yellow autumn leaf colours in mountain birch. The tree's autumnal colour change was brought forward if the tree matured plenty of female catkins. Since yellow colour pigments in leaves are unmasked as leaf nitrogen is re-translocated, sexual reproduction may alter resource allocation at times of leaf senescence. Thus, our current view on the reasons for leaf senescence has to be re-examined, and a novel evolutionary explanation is needed for the appearance of yellow autumn leaf colours.     

Enhanced behavioral sensitivity to the competitive GABA agonist, gaboxadol, in transgenic mice over-expressing hippocampal extrasynaptic alpha6beta GABA(A) receptors

The behavioral and functional significance of the extrasynaptic inhibitory GABA(A) receptors in the brain is still poorly known. We used a transgenic mouse line expressing the GABA(A) receptor alpha6 subunit gene in the forebrain under the Thy-1.2 promoter (Thy1alpha6) mice ectopically expressing alpha6 subunits especially in the hippocampus to study how extrasynaptically enriched alphabeta(gamma2)-type receptors alter animal behavior and receptor responses. In these mice extrasynaptic alpha6beta receptors make up about 10% of the hippocampal GABA(A) receptors resulting in imbalance between synaptic and extrasynaptic inhibition. The synthetic GABA-site competitive agonist gaboxadol (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol; 3 mg/kg) induced remarkable anxiolytic-like response in the light : dark exploration and elevated plus-maze tests in Thy1alpha6 mice, while being almost inactive in wild-type mice. The transgenic mice also lost quicker and for longer time their righting reflex after 25 mg/kg gaboxadol than wild-type mice. In hippocampal sections of Thy1alpha6 mice, the alpha6beta receptors could be visualized autoradiographically by interactions between gaboxadol and GABA via [(35)S]TBPS binding to the GABA(A) receptor ionophore. Gaboxadol inhibition of the binding could be partially prevented by GABA. Electrophysiology of recombinant GABA(A) receptors revealed that GABA was a partial agonist at alpha6beta3 and alpha6beta3delta receptors, but a full agonist at alpha6beta3gamma2 receptors when compared with gaboxadol. The results suggest strong behavioral effects via selective pharmacological activation of enriched extrasynaptic alphabeta GABA(A) receptors, and the mouse model represents an example of the functional consequences of altered balance between extrasynaptic and synaptic inhibition.     

Enhancing bioremediation of diesel-fuel-contaminated soil in a boreal climate: Comparison of biostimulation and bioaugmentation

Cold conditions delay bioremediation of oil hydrocarbons, but other bottlenecks also affect the outcome. Means to stimulate biodegradation of diesel oil hydrocarbons in contaminated soil were compared. Different combinations of nutrients, bulking agent, aeration, and microbial inocula were examined in lab simulations, and effective combinations were tested in field conditions. Bacterial communities were investigated by cloning and sequencing 16S-rRNA genes. Efficient degradation was attained when slow-release nutrients and aeration were used simultaneously. Bacterial inocula did not advance soil remediation, nor did they have any lasting effect on bacterial densities. Bacteria belonging to Proteobacteria were dominant in all cases. In the field test, a bulking agent promoting air passage through the soil ensured sufficient aeration, while forced air decreased the soil moisture excessively. We concluded that biostimulation via optimization of nitrogen and oxygen supply significantly improved bioremediation of oil-contaminated soil, while bioaugmentation had no additional effect.     

Genotypic variation in yellow autumn leaf colours explains aphid load in silver birch

? It has been suggested that autumn-migrating insects drive the evolution of autumn leaf colours. However, evidence of genetic variation in autumn leaf colours in natural tree populations and the link between the genetic variation and herbivore abundances has been lacking. ? Here, we measured the size of the whole aphid community and the development of green-yellow leaf colours in six replicate trees of 19 silver birch (Betula pendula) genotypes at the beginning, in the middle and at the end of autumn colouration. We also calculated the difference between green leaf and leaf litter nitrogen (N) and estimated the changes in phloem sap N loading. ? Autumn leaf colouration had significant genetic variation. During the last survey, genotypes that expressed the strongest leaf reflectance 2-4 wk earlier had an abundance of egg-laying Euceraphis betulae females. Surprisingly, the aphid community size during the first surveys explained N loss by the litter of different birch genotypes. ? Our results are the first evidence at the tree intrapopulation genotypic level that autumn-migrating pests have the potential to drive the evolution of autumn leaf colours. They also stress the importance of recognizing the role of late-season tree-insect interactions in the evolution of herbivory resistance.