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1.
The antimicrobial activity of cryptolepine is influenced by the type of medium employed, agitation and the presence of non-inhibitory concentrations of EDTA. The use of Mueller–Hinton broth (MHB), iso-sensitest broth and tryptone soya broth (TSB) produced lower minimum inhibitory concentrations (MICs) for some of the test organisms compared with nutrient broth or yeast dextrose broth (YDB). For example, a fourfold drop in MIC was recorded for Saccharomyces cerevisiae in MHB compared with the same organism tested in YDB. Agitation of the broths during incubation nearly always produced lower MICs for the bacteria, an eightfold decrease in MIC being recorded for Escherichia coli cultured in nutrient broth with agitation compared with a statically maintained culture. A non-inhibitory concentration (10−3 mol l−1) of disodium EDTA enhanced the antimicrobial activity of cryptolepine. Against E. coli NCTC 11560, an eightfold decrease in MIC and minimum bactericidal concentration (MBC) was recorded when tested in the presence of EDTA.  相似文献   
2.
Globally, river degradation has decimated freshwater fish populations. To help reverse this trend in a southeastern Australia river, we used multiple restoration actions, including reintroduction of instream woody habitat, riparian revegetation, removal of a weir hindering fish movement, fencing out livestock, and controlling riparian weeds. We monitored the responses of native fish at the segment scale (20 km) and reach scale (0.3 km) over 7 years to assess the effectiveness of the different restoration strategies. Two closely related species, Murray cod Maccullochella peeli and trout cod Maccullochella macquariensis, increased at the restored segment compared with the control segment. However, inherent differences between river segments and low sample size hampered assessment of the mechanisms responsible for segment‐scale changes in fish abundance. In contrast, at the reach scale, only M. peeli abundance significantly increased in reaches supplemented with wood. These differential responses by 2 closely related fish species likely reflect species‐specific responses to increased habitat availability and enhanced longitudinal connectivity when the weir improved passage around a fishway. Changes in M. peeli abundance in segments supplemented with and without wood suggest an increase in carrying capacity and not simply a redistribution of individuals within the segment, facilitated the observed expansion. Our findings confirm the need to consider individual fish species' habitat preferences carefully when designing restoration interventions. Further, species‐specific responses to restoration actions provide waterway managers with precise strategies to target fish species for recovery and the potential to predict fish outcomes based on ecological preferences.  相似文献   
3.
Cloud immersion can provide a potentially important moisture subsidy to plants in areas of frequent fog including the threatened spruce-fir communities of the southern Appalachian Mountains (USA). These mountaintop communities grow only above ~1,500 m elevation, harbor the endemic Abies fraseri, and have been proposed to exist because of frequent cloud immersion. While several studies have demonstrated the importance of cloud immersion to plant water balance, no study has evaluated the proportion of plant water derived from cloud moisture in this ecosystem. Using the isotopic mixing model, IsoSource, we analyzed the isotopic composition of hydrogen and oxygen for water extracted from ground water, deep soil, shallow soil, fog, and plant xylem at the upper and lower elevational limits both in May (beginning of the growing season) and October (end of the growing season). Cloud-immersion water contributed up to 31 % of plant water at the upper elevation sites in May. High-elevation plants of both species also experienced greater cloud immersion and had greater cloud water absorption (14–31 %) compared to low-elevation plants (4–17 %). Greater cloud water uptake occurred in May compared to October, despite similar rainfall and cloud-immersion frequencies. These results demonstrate the important water subsidy that cloud-immersion water can provide. With a warming climate leading potentially to increases in the ceiling of the cloud base and, thus, less frequent cloud immersion, persistence of these relic mountaintop forests may depend on the magnitude of these changes and the compensating capabilities of other water sources.  相似文献   
4.
Habitat loss is a major driver of bee declines worldwide, and is of key relevance in the tropics given high deforestation rates, but we continue to have a poor understanding of the impact of land-cover change on tropical bee communities. Orchid bees (Apidae: Euglossini) are critical long-distance pollinators and may be highly susceptible to forest fragmentation given their reliance on forest habitat. Previous studies on the impact of forest fragmentation on euglossines have been geographically limited, have largely ignored β-diversity, and have not compared fragments with continuous forest. To contribute to addressing these gaps, we sampled male euglossine bees in 18 forest fragments (area range: 2.5–33 ha) and at eight locations within a large (3500 ha) continuous forest in the Chocó biodiversity hotspot of Ecuador during the dry season in 2014. We assessed how euglossine abundance, richness, and evenness related to fragment area, isolation, and edge:area ratio. We also compared fragments to continuous forest, in terms of α- and β-diversity. In fragments, a single species (Euglossa tridentata) comprised 78% of captures, and we found no significant effect of fragment area, isolation, or edge on abundance, richness, or evenness among fragments. Forest fragments and continuous forest differed in both community composition and evenness, but not in abundance or species richness. Spatial turnover (β-diversity) showed a non-significant trend toward changing more rapidly in continuous forest relative to fragments. These results underscore the conservation value of continuous forest for orchid bee diversity.  相似文献   
5.
Plants that use the highly efficient C4 photosynthetic pathway possess two types of specialized leaf cells, the mesophyll and bundle sheath. In mature C4 leaves, the CO2 fixation enzyme ribulose-1,5-bisphosphate carboxylase (RuBPCase) is specifically compartmentalized to the bundle sheath cells. However, in very young leaves of amaranth, a dicotyledonous C4 plant, genes encoding the large subunit and small subunit of RuBPCase are initially expressed in both photosynthetic cell types. We show here that the RuBPCase mRNAs and proteins become specifically localized to leaf bundle sheath cells during the developmental transition of the leaf from carbon sink to carbon source. Bundle sheath cell-specific expression of RuBPCase genes and the sink-to-source transition began initially at the leaf apex and progressed rapidly and coordinately toward the leaf base. These findings demonstrated that two developmental transitions, the change in photoassimilate transport status and the establishment of bundle sheath cell-specific RuBPCase gene expression, are tightly coordinated during C4 leaf development. This correlation suggests that processes associated with the accumulation and transport of photosynthetic compounds may influence patterns of photosynthetic gene expression in C4 plants.  相似文献   
6.
The 480 species of leafy spurges, Euphorbia subgenus Esula, represent the main temperate radiation in the large genus Euphorbia. This group is distributed primarily in temperate Eurasia, but with smaller, disjunct centres of diversity in the mountains of the Old World tropics, in temperate southern Africa and in the New World. The majority of New World diversity (32 species) occurs in a single section, section Tithymalus. We analysed sequences of the nrITS and plastid ndhF, trnH‐psbA, trnS‐trnG and trnD‐trnT regions to reconstruct the phylogeny of section Tithymalus and to examine the origins and diversification of the species native to the New World. Our results indicate that the New World species of section Tithymalus form a clade that is sister to the widespread, weedy E. peplus. The New World species fall into two primary groups: a ‘northern annual clade’ from eastern North America and a diverse clade of both annual and perennial species that is divided into three subgroups. Within the second group, there is a small ‘southern annual clade’ from Texas and northern Mexico, a perennial ‘Brachycera clade’ from the western United States and northern Mexico, and a perennial ‘Esuliformis clade’ from montane areas of Mexico, Guatemala, Honduras and the Caribbean island of Hispaniola. Ancestral state reconstructions indicate that the annual habit probably evolved in the ancestor of E. peplus and the New World clade, with a subsequent reversal to the perennial habit. In conjunction with this phylogenetic framework, the New World species of section Tithymalus are comprehensively reviewed. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 191–228.  相似文献   
7.
We study here the permeability of the hydrophobic O2 molecule through a model DPPC bilayer at 323K and 350K, and of the trace amine p-tyramine through PC bilayers at 310K. The tyramine results are compared to previous experimental work at 298K. Nonequilibrium work methods were used in conjunction to simultaneously obtain both the potential of mean force (PMF) and the position dependent transmembrane diffusion coefficient, D(z), from the simulations. These in turn were used to calculate the permeability coefficient, P, through the inhomogeneous solubility-diffusion model. The results for O2 are consistent with previous simulations, and agree with experimentally measured P values for PC bilayers. A temperature dependence in the permeability of O2 through DPPC was obtained, with P decreasing at higher temperatures. Two relevant species of p-tyramine were simulated, from which the PMF and D(z) were calculated. The charged species had a large energetic barrier to crossing the bilayer of ~ 21 kcal/mol, while the uncharged, deprotonated species had a much lower barrier of ~ 7 kcal/mol. The effective in silico permeability for p-tyramine was calculated by applying three approximations, all of which gave nearly identical results (presented here as a function of the pKa). As the permeability value calculated from simulation was highly dependent on the pKa of the amine group, a further pKa study was performed that also varied the fraction of the uncharged and zwitterionic p-tyramine species. Using the experimental P value together with the simulated results, we were able to label the phenolic group as responsible for the pKa1 and the amine for the pKa2, that together represent all of the experimentally measured pKa values for p-tyramine. This agrees with older experimental results, in contrast to more recent work that has suggested there is a strong ambiguity in the pKa values.  相似文献   
8.
OBJECTIVE--To determine whether the risk of the sudden infant death syndrome is increased in bottle fed babies. DESIGN--Population based case-control study matching for age and time. SUBJECTS--All babies aged 1 week to 1 year dying of sudden infant death syndrome during November 1987 to April 1989 or February 1990 to June 1991 and two live controls. SETTING--Avon and north Somerset. MAIN OUTCOME MEASURES--Breast or bottle feeding, sleeping position, maternal smoking, parental employment, and length of gestation. RESULTS--Compared with being fully breast fed, the crude odds ratio for sudden infant death in fully bottle fed babies was 3.1 and for mixed breast and bottle fed babies 1.5. These odds ratios fell to 1.8 (95% confidence interval 0.7 to 4.8) and 1.2 (0.5 to 2.7) respectively after maternal smoking, parental employment, preterm gestation, and sleeping position had been adjusted for. Sleeping position partly masked the effect of being bottle fed on sudden infant death as breast fed babies were more likely to have slept prone than bottle fed babies. CONCLUSIONS--Bottle feeding is not a significant independent risk factor for the sudden infant death syndrome. Patterns of maternal smoking, preterm gestation, and parental employment status account for most of the apparent association with bottle feeding.  相似文献   
9.
Cellulose nanocrystal grafted with chitosan oligosaccharide (CNC-CSOS) was used to encapsulate vitamin C and prepare CNCS/VC complexes using tripolyphosphte via ionic complexation. The stability of vitamin C and the antioxidant activity of the CNCS/VC complexes were elucidated. The formation of the complex was confirmed using DSC and UV–vis spectrophotometry, and TEM was used to study the morphology of the complexes. The encapsulation efficiency of vitamin C at pH 3 and 5 was 71.6% ± 6.8 and 91.0 ± 1.0, respectively. Strong exothermic peaks observed in isothermal titration calorimetric (ITC) studies at pH 5 could be attributed to additional electrostatic interactions between CNC-CSOS and vitamin C at pH 5. The in vitro release of vitamin C from CNCS/VC complexes showed a sustained release of up to 20 days. The vitamin C released from CNCS/VC complex displayed higher stability compared with the control vitamin C solution, and this was also confirmed from the ITC thermograms. CNC-CSOS possessed a higher scavenging activity and faster antioxidant activity compared with its precursors, i.e., oxidized CNC and CSOS and their physical mixtures. Complexing vitamin C into CNC-CSOS particles yielded a dynamic antioxidant agent, where the vitamin C is released over time and displayed sustained antioxidant properties. Therefore, CNCS/VC can potentially be used in cosmeceutical applications as topical formulations.KEY WORDS: cellulose nanocrystals, chitosan oligosaccharide, controlled release, vitamin C antioxidant activity  相似文献   
10.
An affinity matrix for the purification of norsolorinic acid dehydrogenase, an enzyme involved in aflatoxin biosynthesis, was prepared by coupling norsolorinic acid to an agarose gel. This matrix was found to be ineffective in isolating active enzyme, and was therefore modified by methylation, using diazomethane. The methylated matrix produced a one-step purification of the enzyme from a crude homogenate, resulting in a 138-fold purification. The active isolate was found to contain one major and two minor bands upon nondenaturing electrophoresis, and all the norsolorinic acid dehydrogenase activity was associated with the major band. It was concluded that the matrix exhibited true affinity for the enzyme, and that affinity chromatography was a valuable approach to isolating other secondary metabolic enzymes involved in the biosynthesis of the aflatoxins.  相似文献   
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