Heme-heme and heme-ligand interactions in the di-heme oxygen-reducing site of cytochrome bd from Escherichia coli revealed by nanosecond absorption spectroscopy

Cytochrome bd is a terminal quinol:O₂ oxidoreductase of respiratory chains of many bacteria. It contains three hemes, b₅₅₈, b₅₉₅, and d. The role of heme b₅₉₅ remains obscure. A CO photolysis/recombination study of the membranes of Escherichia coli containing either wild type cytochrome bd or inactive E445A mutant was performed using nanosecond absorption spectroscopy. We compared photoinduced changes of heme d-CO complex in one-electron-reduced, two-electron-reduced, and fully reduced states of cytochromes bd. The line shape of spectra of photodissociation of one-electron-reduced and two-electron-reduced enzymes is strikingly different from that of the fully reduced enzyme. The difference demonstrates that in the fully reduced enzyme photolysis of CO from heme d perturbs ferrous heme b₅₉₅ causing loss of an absorption band centered at 435 nm, thus supporting interactions between heme b₅₉₅ and heme d in the di-heme oxygen-reducing site, in agreement with previous works. Photolyzed CO recombines with the fully reduced enzyme monoexponentially with τ ∼ 12 μs, whereas recombination of CO with one-electron-reduced cytochrome bd shows three kinetic phases, with τ ∼ 14 ns, 14 μs, and 280 μs. The spectra of the absorption changes associated with these components are different in line shape. The 14 ns phase, absent in the fully reduced enzyme, reflects geminate recombination of CO with part of heme d. The 14-μs component reflects bimolecular recombination of CO with heme d and electron backflow from heme d to hemes b in ∼ 4% of the enzyme population. The final, 280-μs component, reflects return of the electron from hemes b to heme d and bimolecular recombination of CO in that population. The fact that even in the two-electron-reduced enzyme, a nanosecond geminate recombination is observed, suggests that namely the redox state of heme b₅₉₅, and not that of heme b₅₅₈, controls the pathway(s) by which CO migrates between heme d and the medium.     

A morphological study and hybridization analysis of Caloglossa leprieurii (Ceramiales, Rhodophyta) from Japan, Singapore and Australia

Morphological and hybridization experiments were performed on Caloglossa leprieurii (Montagne) J. Agardh collected from Japan, Singapore and Australia in order to evaluate taxonomic characters of this species. Within C. leprieurii at least four mating groups were recognized from the Indo-Pacific region. These mating groups could be characterized by the blade width at the inter-node and the cell-row numbers on the opposite side derived from the first axial cell at the main axis, though these properties showed a certain variability even in the same plant under both field and culture conditions. The phylogenetic relationship and geographic distribution of the four mating groups are discussed.     

应用正交试验筛选玫瑰茎段增殖培养基

以玫瑰茎段为试材,6-BA、NAA、GA3及蔗糖为试验因子,每因子设置3个含量水平,以不同培养基的增殖系数为测定指标,通过L9(3^4)正交试验,筛选出1种宜于玫瑰茎段增殖培养的理想培养基,即MS 6-BA1．0mg／L NAA0．01mg／L GA30．05mg／L 蔗糖35g／L。     

Seasonal nitrogen and carbon concentrations in white,brown and woody fine roots of sugar maple (Acer saccharum Marsh)

Small diameter (<1.0-mm) Acer saccharum Marsh roots were separated into white, brown and woody development state classes and analyzed for total N and C concentrations in April, July and October of 1988. White roots had greater concentrations of N and C than either brown or woody roots at each sampling date, and the N concentration of brown roots was consistently greater than that of woody roots. There were no temporal changes in N concentrations in any of the roots. C was slightly elevated in mid-summer in all three classes of roots. The data suggest the possible existence of an N translocation mechanism in ageing and developing fine roots. More research should be undertaken to establish the mechanisms of N loss in developing fine roots.     

东部草原露天矿区粘土改良模拟研究

以我国东部草原露天矿区粘土为研究对象,采用盆栽试验方法,以粘土与表土和沙土混合物为培养基质,三叶草(Trifolium repens Linn)为供试植物,研究不同比例下三叶草生物量、养分吸收量、土壤理化和生物学性状的差异,为寻找最佳配比提供依据。结果表明:不同混合比例显著影响三叶草生物量,粘土+表土(1∶1、1∶2和1∶3)生物量最高(26.5—40.0 g/盆),平均为31.2 g/盆,粘土+沙土(1∶1、1∶2和1∶3)次之(14.9—20.3 g/盆),平均为18.9 g/盆,粘土、沙土和表土平均分别是9.0、5.4 g/盆和41.7 g/盆,同样地,粘土+表土混合基质上三叶草氮吸收量平均为1071 mg/盆,分别是粘土+沙土、粘土和沙土氮吸收量660、321 mg/盆和190 mg/盆的1.62、3.34倍和5.64倍,磷和钾吸收量具有相似变化规律,这与三叶草根直径、根长、根表面积和根尖数有显著关联性;粘土和表土与粘土和沙土混合基质的容重和最大持水量分别显著下降7.4%—21.5%和24.5%—71.8%,饱和入渗率、孔隙度和标准化平均重量直径分别显著增加26.9%—96.3%、45%—218%和34%—72%;全氮、有机质、速效磷、速效钾、饱和电导率显著增加23.0%—88.3%、25.1%—146%、44.0%—91.5%、70.3%—114.8%和3.5%—59.3%;磷酸酶、脲酶、蔗糖酶、硝酸还原酶和固氮酶活性显著提高45.5%—105%、65.2%—172.3%、160%—252%、53.4%—62.7%和197%—374%;真菌、细菌和放线菌数量增幅为119%—142%、93.5%—107%和83%—147%。相关性分析表明,生物量与土壤理化性状、酶活性和微生物数量呈显著或极显著正相关,表现为粘土+表土=表土粘土+沙土粘土沙土。因此,表土或沙土均能改良粘土性状,其中粘土和表土1∶2配比效果最优。     

Enhanced Phytoremediation Capacity of Chenopodium album L. Grown on Pb-Contaminated Soils Using EDTA and Reduction of Leaching Risk

Leaching of metals due to enhanced mobility during ethylenediaminetetraacetic acid (EDTA)-assisted phytoextraction has been demonstrated as one of the potential hazards associated with this technology. This study was conducted to determine phytoextraction efficiency of Chenopodium album L. for Pb and EDTA-assisted (1.5, 3, and 9 mmol kg^?1) phytoextraction and potential for leaching of Pb. The results demonstrated that BCF_shoot (bioconcentration factor) was relatively higher than the BCF_root. Translocation factor in the shoot was higher than the roots. Thus, plant species would be applicable for Pb phytoextraction. EDTA enhanced translocation of Pb from roots to shoots. Lead content in the plant parts was maximum in the shoot and root of 9EDTA and 3EDTA, respectively. However, there was no significant difference between 3EDTA and 9EDTA. Lead concentration in the plant parts increased significantly from vegetative stage into flowering stage. Lead content taken up by the plant was lowest when EDTA was applied in a single dose. Therefore, application of EDTA in several increments rather than a single split reduced the leaching risk. Totally, optimum phytoextraction was observed when 3 mmol kg^?1 EDTA was added in triple dosage 60 days after the plant cultivation under triple application mode. The results indicated the plant has the potential for Pb phytoextraction, but it should not be used unless the biomass containing such accumulated metal is removed for disposal. Significant improvement over current ETDA-assisted phytoextraction of Pb may be possible but should be implemented cautiously because of environmental risk.     

Males paving the road to polyandry? Parental compensation in a monogamous nesting cuckoo and a classical polyandrous relative

Comparative studies have established the necessity for biparental care as an important factor for monogamy in freshwater fish and birds. However, whether two parents are really needed for offspring care remains an open question in many cases. I experimentally studied female and male contributions to offspring care in the white-browed coucal (Centropus superciliosus), a monogamous and biparental cuckoo with a balanced adult sex ratio, and contrasted it with the sympatric black coucal (C. grillii), a classically polyandrous species with a male-biased adult sex ratio and male-only care. To study the necessity for biparental care, I temporarily removed one partner for 2 days to see whether the remaining parent compensated for the absence of its partner. Both female and male white-browed coucals approximately doubled their feeding rates when their partner was absent, thus fully compensating the number of feeding visits to the nest. However, nestlings maintained their growth only, when males were present and females were removed. When males were removed and only females were present, nestling growth declined. Hence, only male white-browed coucals fully compensated for the temporary loss of the partner, suggesting that females could benefit most from nesting with additional males—if these should become available. Removing female black coucals had no consequence for nestling feeding rates of male black coucals. But male black coucals had to be returned to their territories within a few hours to avoid harming the brood because female black coucals typically would not commence feeding their offspring. In conclusion, the breeding system of white-browed coucals seems quite flexible and the relatively balanced adult sex ratio may stabilize monogamy in this species. Should ecological factors ever favour a stronger bias in the adult sex ratio towards males, female white-browed coucals may easily become polyandrous and relinquish parental care entirely to males.     

Better safe than sorry: The response to a simulated predator and unfamiliar scent by the European hare

Predator presence can create a “landscape of fear,” which is defined as the spatially explicit distribution of perceived predation risk as seen by prey. Prey species can alter their behavior and space use as a response to increased predation risk, which might be traded off with energetic requirements. Thus, whether or not an anti-predator behavior is performed might depend on the perceived risk. In this study, we investigated the behavioral and spatial response of the European hare (Lepus europaeus) toward the presence of a predator scent, using red fox (Vulpes vulpes) scat, an unfamiliar control scent (butyric acid), and a true control (no scent). We collected data on hare activity times and behavior using 50 camera trap locations and spatial data using GPS telemetry (30,481 GPS positions of 12 hares). Hares showed spatial anti-predator behaviors within their home range, for example, the local avoidance of areas treated with scent and remaining further from field edges, in response to sympatric predator scent and partly also in response to unfamiliar butyric acid. Conversely, more costly anti-predator behaviors, that is, increased vigilance at the expense of foraging, were only shown in response to the predator scent. Our results suggest that prey species respond flexibly toward scent cues, utilizing less costly anti-predator behaviors independent of the perceived threat, whereas costly anti-predator responses are only used in the presence of “real” threat. Further, our findings emphasize that a combination of camera trap and GPS data can provide detailed information on animal behavior and space use, and caution that interpretation of one data source alone might lead to incomplete conclusions.     

Higher seed size and germination rate may favour autotetraploids of Vicia cracca L. (Fabaceae)

The phenotypic effect of increased cell size in polyploid angiosperms has been repeatedly described; the ecological consequences of the gigas effect are, however, relatively poorly understood. Here, we investigated the effect of cytotype, seed weight, and inter‐population variation on seedling germination and growth in diploid and autotetraploid Vicia cracca L. in a common garden experiment. Seeds used in this study originated in the contact zone of the cytotypes in Central Europe. Tetraploids had heavier seeds than diploids and greater germination rates irrespective of seed size. Both seed weight and germination rate displayed high inter‐population variation. Further, tetraploids seem to germinate earlier and deposit fewer reserves into the seed bank than diploids. Mean above‐ground biomass and seedling height were similar in the two cytotypes of V. cracca. Nonetheless, the tallest tetraploid seedlings were taller than the tallest diploid seedlings, which may be advantageous under strong competition in dense vegetation. This study thus demonstrates that tetraploids of V. cracca may have superior competitive ability to diploids in certain habitats. It also suggests the necessity of studying multiple populations per cytotype when comparing diploids and polyploids, as the effect of population may be of similar or even higher magnitude than the effect of cytotype. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 57–73.     

Molecular basis for ATPase-powered substrate translocation by the Lon AAA+ protease

The Lon AAA+ (adenosine triphosphatases associated with diverse cellular activities) protease (LonA) converts ATP-fuelled conformational changes into sufficient mechanical force to drive translocation of a substrate into a hexameric proteolytic chamber. To understand the structural basis for the substrate translocation process, we determined the cryo-electron microscopy (cryo-EM) structure of Meiothermus taiwanensis LonA (MtaLonA) in a substrate-engaged state at 3.6 Å resolution. Our data indicate that substrate interactions are mediated by the dual pore loops of the ATPase domains, organized in spiral staircase arrangement from four consecutive protomers in different ATP-binding and hydrolysis states. However, a closed AAA+ ring is maintained by two disengaged ADP-bound protomers transiting between the lowest and highest position. This structure reveals a processive rotary translocation mechanism mediated by LonA-specific nucleotide-dependent allosteric coordination among the ATPase domains, which is induced by substrate binding.