Relative Dominance Affects Use of Scent-Marked Areas in Male Snow Voles Chionomys nivalis

We conducted a laboratory experiment to examine whether dominance status affects the use of locations occupied (i.e. scent-marked) by same-sex conspecifics among wild-caught snow vole males ( Chionomys nivalis ). Given that the costs of invading scent-marked areas should partially depend on the intruder's competitive ability, we hypothesised that, once a dominance relationship has been established with the owner of marks, the use of these areas by males would vary differently between dominant and subordinate individuals. Before any previous experience with the owner, scented substrates and nests were highly attractive to all males, indicating a general preference for recently occupied areas. However, after relative social status was established through direct interaction the subsequent response of males was altered differently, subordinate individuals reducing the use of marked areas to a much greater extent than dominants. Competitive relationships between male C. nivalis were found to be influenced by differences in body weight, larger males tending to display a more dominant pattern of behaviour. Our results reveal that male C. nivalis may require some direct experience with potential opponents to modulate their response towards occupied locations. Additionally, we suggest that the ability of males to conditionally respond to social signals from particular competing conspecifics might be used to lower the costs of prospective agonistic interactions.     

Glutamate Oxidation by Soybean Cotyledon and Leaf Mitochondria

Mitochondria purified from cotyledons of soybean seedlings fiveto ten days old have the capacity to rapidly oxidize glutamate(measured as glutamate dependent oxygen consumption). This capacitywas greatest at ten days after planting but was very low priorto emergence of cotyledons from the vermiculite and during senescence.Solubilized glutamate dehydrogenase activity, on the other hand,was substantial at two days after planting, peaked at sevendays, then declined and rose again during senescence. It issuggested that mitochondrial glutamate oxidation plays a rolein reserve mobilization and amino acid metabolism during seedlinggrowth. Leaf mitochondria and those from senescing cotyledonscould not sustain rapid rates of glutamate oxidation despiteready oxidation of other substrates and high solubilized glutamatedehydrogenase activity, suggesting an alternative role for theenzyme in these tissues. Possible controlling factors are discussed. ² Present address, Garvan Institute, Darlinghurst, N. S. W.,Australia. ³ Permanent address, Department de Biologia Vegetal, Facultatde Biologia, Universitat de Barcelona, Barcelona, Spain. (Received May 6, 1988; Accepted August 3, 1988)     

Thermodynamic approach to biomass distribution in ecological systems

In the derivation of the biomass distribution function for an ecological population critical use is made of an energetic constraint on the maximization of biomass diversity. The nature of this constraint is explored in detail using Kleiber's relation σ(m)=cm ^γ between animal metabolic rate σ(m) and body weightm in conjuction with the Prigogine-Wiame thermodynamic paradigm for specific entropy production in biological stationary states. These two inputs fix the energetic constraint on the maximization of biomass diversity to be the constancy of the mean metabolic rate of the ecosystem. The resulting biomass distribution function is tested against observational data.     

Supercritical carbon dioxide extraction of hydrocarbons from the microalgaBotryococcus braunii

Samples of the microalgaBotryococcus braunii were submitted to supercritical fluid extraction with carbon dioxide at 40 °C and pressures of 12.5, 20.0 and 30.0 MPa. The extraction yield and the fraction of the hydrocarbons in the extracts both increased with pressure and at 30 MPa these compounds were obtained rapidly. This behaviour is associated with the localization of the hydrocarbons outside the cell wall. In the extracts, which are fluid, golden and limpid, chlorophyll and phospholipids were not detected.Author for correspondence     

Size-fractionated biomass, photosynthesis and dark CO2 fixation in a tropical oceanic environment

This study examines the spatial distribution and size structureof phytoplankton biomass and productivity in relation to thevertical structrure of the Andaman Sea (northeastern IndianOcean). This region was characterized by low concentrationsof nutrients and high levels of insolation. Nitrogen availabilityappeared to control overall productivity with nitrate-based‘new’ production accounting for 8–24% of thetotal primary production. Euphotic column chlorophyll (chl a)averaged 52.5 mg m^–2 of which a major portion was locatedas a subsurface chl a maximum (SCM) at     

Occurrence of Verticillium fungicola var. fungicola on Agaricus bitorquis Mushroom Crops in Spain

Diseased fruit bodies of Agaricus bitorquis, with similar symptoms to those caused by dry bubble on Agaricus bisporus, were observed in some Spanish crops during summer 1999. Isolates of Verticillium fungicola from A. bitorquis and A. bisporus were submitted to different temperatures and to prochloraz–Mn sensitivity tests. All the isolates collected from A. bitorquis and A. bisporus were identified as V. fungicola var. fungicola. Artificial infections of A. bisporus and A. bitorquis with V. fungicola var. fungicola are also described in the present study. The appearance of natural infections of V. fungicola var. fungicola in A. bitorquis crops could well be due to the growing temperatures used in Spain, which are considerably below those used in other countries.     

Caffeine has a dual influence on NMDA receptor–mediated glutamatergic transmission at the hippocampus

Caffeine, a stimulant largely consumed around the world, is a non-selective adenosine receptor antagonist, and therefore caffeine actions at synapses usually, but not always, mirror those of adenosine. Importantly, different adenosine receptors with opposing regulatory actions co-exist at synapses. Through both inhibitory and excitatory high-affinity receptors (A₁R and A₂R, respectively), adenosine affects NMDA receptor (NMDAR) function at the hippocampus, but surprisingly, there is a lack of knowledge on the effects of caffeine upon this ionotropic glutamatergic receptor deeply involved in both positive (plasticity) and negative (excitotoxicity) synaptic actions. We thus aimed to elucidate the effects of caffeine upon NMDAR-mediated excitatory post-synaptic currents (NMDAR-EPSCs), and its implications upon neuronal Ca²⁺ homeostasis. We found that caffeine (30–200 μM) facilitates NMDAR-EPSCs on pyramidal CA1 neurons from Balbc/ByJ male mice, an action mimicked, as well as occluded, by 1,3-dipropyl-cyclopentylxantine (DPCPX, 50 nM), thus likely mediated by blockade of inhibitory A₁Rs. This action of caffeine cannot be attributed to a pre-synaptic facilitation of transmission because caffeine even increased paired-pulse facilitation of NMDA-EPSCs, indicative of an inhibition of neurotransmitter release. Adenosine A_2ARs are involved in this likely pre-synaptic action since the effect of caffeine was mimicked by the A_2AR antagonist, SCH58261 (50 nM). Furthermore, caffeine increased the frequency of Ca²⁺ transients in neuronal cell culture, an action mimicked by the A₁R antagonist, DPCPX, and prevented by NMDAR blockade with AP5 (50 μM). Altogether, these results show for the first time an influence of caffeine on NMDA receptor activity at the hippocampus, with impact in neuronal Ca²⁺ homeostasis.

     

Spatial modeling of techno‐economic potential of biojet fuel production in Brazil

It is expected that Brazil could play an important role in biojet fuel (BJF) production in the future due to the long experience in biofuel production and the good agro‐ecological conditions. However, it is difficult to quantify the techno‐economic potential of BJF because of the high spatiotemporal variability of available land, biomass yield, and infrastructure as well as the technological developments in BJF production pathways. The objective of this research is to assess the recent and future techno‐economic potential of BJF production in Brazil and to identify location‐specific optimal combinations of biomass crops and technological conversion pathways. In total, 13 production routes (supply chains) are assessed through the combination of various biomass crops and BJF technologies. We consider temporal land use data to identify potential land availability for biomass production. With the spatial distribution of the land availability and potential yield of biomass crops, biomass production potential and costs are calculated. The BJF production cost is calculated by taking into account the development in the technological pathways and in plant scales. We estimate the techno‐economic potential by determining the minimum BJF total costs and comparing this with the range of fossil jet fuel prices. The techno‐economic potential of BJF production ranges from 0 to 6.4 EJ in 2015 and between 1.2 and 7.8 EJ in 2030, depending on the reference fossil jet fuel price, which varies from 19 to 65 US$/GJ across the airports. The techno‐economic potential consists of a diverse set of production routes. The Northeast and Southeast region of Brazil present the highest potentials with several viable production routes, whereas the remaining regions only have a few promising production routes. The maximum techno‐economic potential of BJF in Brazil could meet almost half of the projected global jet fuel demand toward 2030.     

Structural and biophysical characterization of the tandem substrate-binding domains of the ABC importer GlnPQ

The ATP-binding cassette transporter GlnPQ is an essential uptake system that transports glutamine, glutamic acid and asparagine in Gram-positive bacteria. It features two extra-cytoplasmic substrate-binding domains (SBDs) that are linked in tandem to the transmembrane domain of the transporter. The two SBDs differ in their ligand specificities, binding affinities and their distance to the transmembrane domain. Here, we elucidate the effects of the tandem arrangement of the domains on the biochemical, biophysical and structural properties of the protein. For this, we determined the crystal structure of the ligand-free tandem SBD1-2 protein from Lactococcus lactis in the absence of the transporter and compared the tandem to the isolated SBDs. We also used isothermal titration calorimetry to determine the ligand-binding affinity of the SBDs and single-molecule Förster resonance energy transfer (smFRET) to relate ligand binding to conformational changes in each of the domains of the tandem. We show that substrate binding and conformational changes are not notably affected by the presence of the adjoining domain in the wild-type protein, and changes only occur when the linker between the domains is shortened. In a proof-of-concept experiment, we combine smFRET with protein-induced fluorescence enhancement (PIFE–FRET) and show that a decrease in SBD linker length is observed as a linear increase in donor-brightness for SBD2 while we can still monitor the conformational states (open/closed) of SBD1. These results demonstrate the feasibility of PIFE–FRET to monitor protein–protein interactions and conformational states simultaneously.     

Sensitivity of Aspergillus nidulans to the Cellulose Synthase Inhibitor Dichlobenil: Insights from Wall-Related Genes’ Expression and Ultrastructural Hyphal Morphologies

The fungal cell wall constitutes an important target for the development of antifungal drugs, because of its central role in morphogenesis, development and determination of fungal-specific molecular features. Fungal walls are characterized by a network of interconnected glycoproteins and polysaccharides, namely α-, β-glucans and chitin. Cell walls promptly and dynamically respond to environmental stimuli by a signaling mechanism, which triggers, among other responses, modulations in wall biosynthetic genes’ expression. Despite the absence of cellulose in the wall of the model filamentous fungus Aspergillus nidulans, we found in this study that fungal growth, spore germination and morphology are affected by the addition of the cellulose synthase inhibitor dichlobenil. Expression analysis of selected genes putatively involved in cell wall biosynthesis, carried out at different time points of drug exposure (i.e. 0, 1, 3, 6 and 24 h), revealed increased expression for the putative mixed linkage β-1,3;1,4 glucan synthase celA together with the β-1,3-glucan synthase fksA and the Rho-related GTPase rhoA. We also compared these data with the response to Congo Red, a known plant/fungal drug affecting both chitin and cellulose biosynthesis. The two drugs exerted different effects at the cell wall level, as shown by gene expression analysis and the ultrastructural features observed through atomic force microscopy and scanning electron microscopy. Although the concentration of dichlobenil required to affect growth of A. nidulans is approximately 10-fold higher than that required to inhibit plant cellulose biosynthesis, our work for the first time demonstrates that a cellulose biosynthesis inhibitor affects fungal growth, changes fungal morphology and expression of genes connected to fungal cell wall biosynthesis.