Secondary succession of plant communities in a subtropical mountainous region of SW China

Since 1985, originally forested mountainous areas of China have been allowed to return to their natural state after years of exploitation including agriculture, development, and logging. The reforms began earlier in less accessible locations, so that today the successional process is more advanced there. The vegetation in Luquan, Qiongzhusi, and Xishan near Kunming, central Yunnan, exhibits, in a limited area, a range of stages of plant succession that are widely encountered throughout the broader region, and thus affords a special opportunity for a comprehensive study. We analyzed the successional sequence of these various plant communities. They ranged from pioneer coniferous and/or pioneer deciduous broad-leaved stands to pre-mature semi-humid evergreen broad-leaved stands, through mixed coniferous and broad-leaved or mixed deciduous and evergreen broad-leaved stands. The succession proceeded from pioneer coniferous Pinus and Keteleeria, and deciduous Platycarya and Alnus, to late-successional evergreen broad-leaved Cyclobalanopsis and Castanopsis. Two regeneration types of woody species in either the early successional (15–50 years), the mid-successional (40–80 years), or the late-successional (80–180 years) stage were classified. Relatively high species diversity was found in the seral phase at the three study sites. The late-successional stage was commonest where human disturbance was least evident. Poor soil chemical properties under pioneer Pinus were seen as a limitation to plant growth, while the abundance of Alnus at the early stage led to an improved level of organic matter and nitrogen.     

Improving the accuracy of a solid spherical source radius and depth estimation using the diffusion equation in fluorescence reflectance mode

Background  

Non-invasive planar fluorescence reflectance imaging (FRI) is used for accessing physiological and molecular processes in biological tissue. This method is efficiently used to detect superficial fluorescent inclusions. FRI is based on recording the spatial radiance distribution (SRD) at the surface of a sample. SRD provides information for measuring structural parameters of a fluorescent source (such as radius and depth). The aim of this article is to estimate the depth and radius of the source distribution from SRD, measured at the sample surface. For this reason, a theoretical expression for the SRD at the surface of a turbid sample arising from a spherical light source embedded in the sample, was derived using a steady-state solution of the diffusion equation with an appropriate boundary condition.     

Entomopathogenic fungi as a potential control agent against the lesser mealworm, <Emphasis Type="Italic">Alphitobius diaperinus</Emphasis> in broiler houses

We tested the pathogenicity of 18 Metarhizium anisopliae (Metschn.) Sorokin isolates and 22 Beauveria bassiana (Balsamo) Vuillemin isolates against Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae) larvae and adults. The efficacy of the most virulent isolate—M. anisopliae K—was evaluated in containers with a concrete bottom covered with wood shavings, under simulated poultry house conditions. Application of conidia of this isolate to the shavings or directly to the concrete bottom reduced the yield of larvae in 8–15 time compared with the control. In another test, the mortality of mature larvae placed on previously inoculated shavings or bottom reached 80–90% within 14 days, compared with 14% in the control. The residual activity of conidia kept at 28°C retained its initial level during 14 days post-inoculation, but declined after three weeks. Based on our data M. anisopliae has considerable potential for the control of A. diaperinus.

Recognition of mitochondrial targeting sequences by the import receptors Tom20 and Tom22

The Tom20 and Tom22 receptor subunits of the TOM (translocase of the outer mitochondrial membrane) complex recognize N-terminal presequences of proteins that are to be imported into the mitochondrion. In plants, Tom20 is C-terminally anchored in the mitochondrial membrane, whereas Tom20 is N-terminally anchored in animals and fungi. Furthermore, the cytosolic domain of Tom22 in plants is smaller than its animal/fungal counterpart and contains fewer acidic residues. Here, NMR spectroscopy was used to explore presequence interactions with the cytosolic regions of receptors from the plant Arabidopsis thaliana and the fungus Saccharomyces cerevisiae (i.e., AtTom20, AtTom22, and ScTom22). It was found that AtTom20 possesses a discontinuous bidentate hydrophobic binding site for presequences. The presequences on plant mitochondrial proteins comprise two or more hydrophobic binding regions to match this bidentate site. NMR data suggested that while these presequences bind to ScTom22, they do not bind to AtTom22. AtTom22, however, binds to AtTom20 at the same binding site as presequences, suggesting that this domain competes with the presequences of imported proteins, thereby enabling their progression along the import pathway.     

Ion channel noise can explain firing correlation in auditory nerves

Sensory neurons code information about stimuli in their sequence of action potentials (spikes). Intuitively, the spikes should represent stimuli with high fidelity. However, generating and propagating spikes is a metabolically expensive process. It is therefore likely that neural codes have been selected to balance energy expenditure against encoding error. Our recently proposed optimal, energy-constrained neural coder (Jones et al. Frontiers in Computational Neuroscience, 9, 61 2015) postulates that neurons time spikes to minimize the trade-off between stimulus reconstruction error and expended energy by adjusting the spike threshold using a simple dynamic threshold. Here, we show that this proposed coding scheme is related to existing coding schemes, such as rate and temporal codes. We derive an instantaneous rate coder and show that the spike-rate depends on the signal and its derivative. In the limit of high spike rates the spike train maximizes fidelity given an energy constraint (average spike-rate), and the predicted interspike intervals are identical to those generated by our existing optimal coding neuron. The instantaneous rate coder is shown to closely match the spike-rates recorded from P-type primary afferents in weakly electric fish. In particular, the coder is a predictor of the peristimulus time histogram (PSTH). When tested against in vitro cortical pyramidal neuron recordings, the instantaneous spike-rate approximates DC step inputs, matching both the average spike-rate and the time-to-first-spike (a simple temporal code). Overall, the instantaneous rate coder relates optimal, energy-constrained encoding to the concepts of rate-coding and temporal-coding, suggesting a possible unifying principle of neural encoding of sensory signals.     

Hydro and halo priming: influenced germination responses in wheat Var-HUW-468 under heavy metal stress

The beneficial effect of seed priming in improving critical growth stages like seed germination and early growth phases has been accepted by Plant Physiologists for many important field crops. In the present investigation, studies were made to see the effect of heavy metal stress imposed during germination using solution of HgCl₂ in four different concentrations (0.0, 0.50, 0.75 and 1.00 mM) in Petri dishes on primed and non-primed seeds of wheat. Priming has been done with distilled water (hydro), Mg(NO₃)₂ and Ca(NO₃)₂ (halo) salts. Different germination parameters, such as germination percentage, radicle and plumule lengths, seedling emergence, soluble and insoluble sugar contents and activity of α-amylase in endosperm were studied at different study periods. Primed seeds increased all the germination parameters except insoluble sugar content in respect to non-primed control in the absence of HgCl₂. However, the use of primed seeds has shown to overcome the inhibitory effects of heavy metal stress imposed in the form of HgCl₂ solution during the period of germination. Hence, the work concludes the mitigating effects of priming under heavy metal stress.     

YphC and YsxC GTPases assist the maturation of the central protuberance,GTPase associated region and functional core of the 50S ribosomal subunit

YphC and YsxC are GTPases in Bacillus subtilis that facilitate the assembly of the 50S ribosomal subunit, however their roles in this process are still uncharacterized. To explore their function, we used strains in which the only copy of the yphC or ysxC genes were under the control of an inducible promoter. Under depletion conditions, they accumulated incomplete ribosomal subunits that we named 45S_YphC and 44.5S_YsxC particles. Quantitative mass spectrometry analysis and the 5–6 Å resolution cryo-EM maps of the 45S_YphC and 44.5S_YsxC particles revealed that the two GTPases participate in the maturation of the central protuberance, GTPase associated region and key RNA helices in the A, P and E functional sites of the 50S subunit. We observed that YphC and YsxC bind specifically to the two immature particles, suggesting that they represent either on-pathway intermediates or that their structure has not significantly diverged from that of the actual substrate. These results describe the nature of these immature particles, a widely used tool to study the assembly process of the ribosome. They also provide the first insights into the function of YphC and YsxC in 50S subunit assembly and are consistent with this process occurring through multiple parallel pathways, as it has been described for the 30S subunit.     

Quantification of Metabolic Rearrangements During Neural Stem Cells Differentiation into Astrocytes by Metabolic Flux Analysis

Proliferation and differentiation of neural stem cells (NSCs) have a crucial role to ensure neurogenesis and gliogenesis in the mammalian brain throughout life. As there is growing evidence for the significance of metabolism in regulating cell fate, knowledge on the metabolic programs in NSCs and how they evolve during differentiation into somatic cells may provide novel therapeutic approaches to address brain diseases. In this work, we applied a quantitative analysis to assess how the central carbon metabolism evolves upon differentiation of NSCs into astrocytes. Murine embryonic stem cell (mESC)-derived NSCs and astrocytes were incubated with labelled [1-¹³C]glucose and the label incorporation into intracellular metabolites was followed by GC-MS. The obtained ¹³C labelling patterns, together with uptake/secretion rates determined from supernatant analysis, were integrated into an isotopic non-stationary metabolic flux analysis (¹³C-MFA) model to estimate intracellular flux maps. Significant metabolic differences between NSCs and astrocytes were identified, with a general downregulation of central carbon metabolism during astrocytic differentiation. While glucose uptake was 1.7-fold higher in NSCs (on a per cell basis), a high lactate-secreting phenotype was common to both cell types. Furthermore, NSCs consumed glutamine from the medium; the highly active reductive carboxylation of alpha-ketoglutarate indicates that this was converted to citrate and used for biosynthetic purposes. In astrocytes, pyruvate entered the TCA cycle mostly through pyruvate carboxylase (81%). This pathway supported glutamine and citrate secretion, recapitulating well described metabolic features of these cells in vivo. Overall, this fluxomics study allowed us to quantify the metabolic rewiring accompanying astrocytic lineage specification from NSCs.