Contrasting effects of plant population size on florivory and pollination

Changes in plant population size, induced by various forms of habitat degradation, can affect the performance of plants by altering their interactions with other organisms such as pollinators and herbivores. However, studies on plant reproductive response to variation in population size that simultaneously consider different interactions are rare. In this study, we examined (1) how levels of pollinator visitation and florivory vary with population size of a self-incompatible herb, Verbascum nigrum (Scrophulariaceae), (2) the relative effect of these two interactions on host seed set, and (3) whether the intensity of florivory influences pollinator visitation rate. The intensity of florivory increased, whereas pollinator visitation rate decreased with host population size. Although average seed production was negatively affected by the intensity of florivory, seed production was independent of population size. The direct negative effect of florivores on plant seed set was indirectly enforced by their negative effect on pollinator visitation rate. Our results emphasize the complexity of responses of different plant–animal interactions to plant population size. However, interactions involving specialized organisms are likely to disrupt first as plant population size decreases.     

Large-scale grazing history effects on Arctic-alpine germinable seed banks

Grazing constitutes a selective pressure on vegetation recruitment through modification of the seed banks. Here we address changes in seed bank density and its life history trait composition in century-old pastures, where contrasting reindeer densities have developed during the last decades. We cover the actual scales used by these wide-roaming herbivores by sampling 70 productive tundra habitats over 7,421 km² in the reindeer summer pastures of Northern Norway. Results showed that the seed bank density was significantly lowered where reindeer densities had increased in recent decades, whereas the century-long history of grazing probably explains the main seed bank traits typical of grazing tolerant plants. The dominant trait characteristics were small seeds (<0.5 mg), seeds lacking dispersal mechanism and individuals with a graminoid growth form. Finally, differences between regions introduced trait variation independent of grazing history, reinforcing the importance of using scales covering several contexts when designing ecological studies.     

Active Site of Cytochrome cbb3

Cytochrome cbb₃ is the most distant member of the heme-copper oxidase family still retaining the following major feature typical of these enzymes: reduction of molecular oxygen to water coupled to proton translocation across the membrane. The thermodynamic properties of the six redox centers, five hemes and a copper ion, in cytochrome cbb₃ from Rhodobacter sphaeroides were studied using optical and EPR spectroscopy. The low spin heme b in the catalytic subunit was shown to have the highest midpoint redox potential (E_m,7 +418 mV), whereas the three hemes c in the two other subunits titrated with apparent midpoint redox potentials of +351, +320, and +234 mV. The active site high spin heme b₃ has a very low potential (E_m,7 -59 mV) as opposed to the copper center (Cu_B), which has a high potential (E_m,7 +330 mV). The EPR spectrum of the ferric heme b₃ has rhombic symmetry. To explain the origins of the rhombicity, the Glu-383 residue located on the proximal side of heme b₃ was mutated to aspartate and to glutamine. The latter mutation caused a 10 nm blue shift in the optical reduced minus oxidized heme b₃ spectrum, and a dramatic change of the EPR signal toward more axial symmetry, whereas mutation to aspartate had far less severe consequences. These results strongly suggest that Glu-383 is involved in hydrogen bonding to the proximal His-405 ligand of heme b₃, a unique interaction among heme-copper oxidases.The heme-copper oxidases form a family of enzymes that have structural homology of the catalytic subunit in common (1). This family of proteins, characterized by six conserved histidine ligands of the redox cofactors, ranges from classical, mitochondrial terminal oxidases to nitric-oxide reductases, and the members have been classified according to evolutionary relationships of their sequences (2–4). The bacterial cbb₃-type cytochrome c oxidases form a distinct, divergent subfamily within the heme-copper oxidases (5). Terminal oxidases share the catalytic activity of four-electron reduction of molecular oxygen to water coupled to translocation of protons across the membrane (6, 7). Cytochrome cbb₃, expressed in some bacteria as a sole terminal oxidase, is characterized by its ability to maintain catalytic activity under low oxygen tension (8), and it has also been shown to have the capacity to translocate protons (9).The Rhodobacter sphaeroides cytochrome cbb₃ is encoded by the ccoNOQP operon composed of four genes (10). The catalytic subunit CcoN homes a binuclear active site composed of a high spin heme b₃ and a nearby copper ion (Cu_B). There are altogether four low spin hemes in the enzyme. In addition to a protoheme (heme b) residing in the vicinity of the active site in subunit CcoN, there are three hemes c present in the soluble domains of the two other transmembrane subunits, a monoheme subunit CcoO and a diheme subunit CcoP (11). There is yet one more membrane-spanning subunit, CcoQ, without bound cofactors (12). Although the catalytic subunit shows homology to the other heme-copper oxidases (13), the other three subunits bear no resemblance to subunits of other types of terminal oxidases. However, subunit CcoO has been shown to have sequence homology with the nitric-oxide reductase subunit NorC (14).The crystal structures of a few heme-copper oxidases have been resolved (15–19), but only structural homology models are currently available for cytochromes cbb₃ (20–23). Apart from the signatures common to all heme-copper oxidases, the sequence alignments have revealed only very few other conserved residues when terminal oxidases are compared. Even though some amino acids, absent from cytochrome cbb₃, have been shown to be of critical importance to the function of the classical heme-copper oxidases, the major functions still remain the same in all of these enzymes.The thermodynamic properties of the cbb₃-type oxidases have been investigated sparsely. Apart from work yielding partial information about the properties of the hemes (11, 24, 25), two more complete studies have been carried out (5, 26). All the hemes in cytochrome cbb₃ were proposed to have high redox potentials, both in the Pseudomonas stutzeri and Bradyrhizobium japonicum enzymes (5, 26). This is also the case in all other studies, except for the enzyme from Rhodothermus marinus, where two low potential redox centers were reported (25). However, little is known about the copper center in the active site (Cu_B). Early Fourier transform infrared (FTIR)² spectroscopic measurements identified the presence of a heme/copper binuclear center in R. sphaeroides cytochrome cbb₃ (11), and more recent resonance Raman and FTIR studies have given additional information about the structure of the active site (27–29).In the absence of deconvoluted spectral components and thereby clear assignments of the redox centers in the cbb₃-type oxidases, and the lack of consensus about their thermodynamic properties, a complete study was required. In this work we have set out to investigate the thermodynamic properties of all the redox centers in cytochrome cbb₃ from R. sphaeroides using a combination of optical and EPR redox titrations with the main focus on the details of the catalytic site. This effort will form a basis for further mechanistic studies.     

Sphingomyelin is associated with kidney disease in type 1 diabetes (The FinnDiane Study)

Diabetic kidney disease, diagnosed by urinary albumin excretion rate (AER), is a critical symptom of chronic vascular injury in diabetes, and is associated with dyslipidemia and increased mortality. We investigated serum lipids in 326 subjects with type 1 diabetes: 56% of patients had normal AER, 17% had microalbuminuria (20?≤?AER?相似文献   

Climate change impacts on wildlife in a High Arctic archipelago – Svalbard,Norway

The Arctic is warming more rapidly than other region on the planet, and the northern Barents Sea, including the Svalbard Archipelago, is experiencing the fastest temperature increases within the circumpolar Arctic, along with the highest rate of sea ice loss. These physical changes are affecting a broad array of resident Arctic organisms as well as some migrants that occupy the region seasonally. Herein, evidence of climate change impacts on terrestrial and marine wildlife in Svalbard is reviewed, with a focus on bird and mammal species. In the terrestrial ecosystem, increased winter air temperatures and concomitant increases in the frequency of ‘rain‐on‐snow’ events are one of the most important facets of climate change with respect to impacts on flora and fauna. Winter rain creates ice that blocks access to food for herbivores and synchronizes the population dynamics of the herbivore–predator guild. In the marine ecosystem, increases in sea temperature and reductions in sea ice are influencing the entire food web. These changes are affecting the foraging and breeding ecology of most marine birds and mammals and are associated with an increase in abundance of several temperate fish, seabird and marine mammal species. Our review indicates that even though a few species are benefiting from a warming climate, most Arctic endemic species in Svalbard are experiencing negative consequences induced by the warming environment. Our review emphasizes the tight relationships between the marine and terrestrial ecosystems in this High Arctic archipelago. Detecting changes in trophic relationships within and between these ecosystems requires long‐term (multidecadal) demographic, population‐ and ecosystem‐based monitoring, the results of which are necessary to set appropriate conservation priorities in relation to climate warming.     

Trophic interactions and abiotic factors drive functional and phylogenetic structure of vertebrate herbivore communities across the Arctic tundra biome

Communities are assembled from species that evolve or colonise a given geographic region, and persist in the face of abiotic conditions and interactions with other species. The evolutionary and colonisation histories of communities are characterised by phylogenetic diversity, while functional diversity is indicative of abiotic and biotic conditions. The relationship between functional and phylogenetic diversity infers whether species functional traits are divergent (differing between related species) or convergent (similar among distantly related species). Biotic interactions and abiotic conditions are known to influence macroecological patterns in species richness, but how functional and phylogenetic diversity of guilds vary with biotic factors, and the relative importance of biotic drivers in relation to geographic and abiotic drivers is unknown. In this study, we test whether geographic, abiotic or biotic factors drive biome‐scale spatial patterns of functional and phylogenetic diversity and functional convergence in vertebrate herbivores across the Arctic tundra biome. We found that functional and phylogenetic diversity both peaked in the western North American Arctic, and that spatial patterns in both were best predicted by trophic interactions, namely vegetation productivity and predator diversity, as well as climatic severity. Our results show that both bottom–up and top–down trophic interactions, as well as winter temperatures, drive the functional and phylogenetic structure of Arctic vertebrate herbivore assemblages. This has implications for changing Arctic ecosystems; under future warming and northward movement of predators potential increases in phylogenetic and functional diversity in vertebrate herbivores may occur. Our study thus demonstrates that trophic interactions can determine large‐scale functional and phylogenetic diversity just as strongly as abiotic conditions.     

Solid-phase extraction or liquid chromatography coupled on-line with gas chromatography in the analysis of biological samples

This review provides an overview of the on-line coupling of solid-phase extraction or liquid chromatography with gas chromatography for the analysis of biological samples. Principles relevant to techniques are briefly presented and selected applications are described. Benefits of the coupled systems are discussed.     

Diacetyl control during brewery fermentation via adaptive laboratory engineering of the lager yeast <Emphasis Type="Italic">Saccharomyces pastorianus</Emphasis>

Diacetyl contributes to the flavor profile of many fermented products. Its typical buttery flavor is considered as an off flavor in lager-style beers, and its removal has a major impact on time and energy expenditure in breweries. Here, we investigated the possibility of lowering beer diacetyl levels through evolutionary engineering of lager yeast for altered synthesis of α-acetolactate, the precursor of diacetyl. Cells were exposed repeatedly to a sub-lethal level of chlorsulfuron, which inhibits the acetohydroxy acid synthase responsible for α-acetolactate production. Initial screening of 7 adapted isolates showed a lower level of diacetyl during wort fermentation and no apparent negative influence on fermentation rate or alcohol yield. Pilot-scale fermentation was carried out with one isolate and results confirmed the positive effect of chlorsulfuron adaptation. Diacetyl levels were over 60% lower at the end of primary fermentation relative to the non-adapted lager yeast and no significant change in fermentation performance or volatile flavor profile was observed due to the adaptation. Whole-genome sequencing revealed a non-synonymous SNP in the ILV2 gene of the adapted isolate. This mutation is known to confer general tolerance to sulfonylurea compounds, and is the most likely cause of the improved tolerance. Adaptive laboratory evolution appears to be a natural, simple and cost-effective strategy for diacetyl control in brewing.