Responses of tropical cladocerans to a gradient of resource quality

1. The response of three tropical cladocerans to a gradient of resource quality was compared in a series of growth bioassays using seston collected from five lakes of different depth and trophic structure in Michigan, U.S.A. To assess the food quality in terms of digestibility, assimilation experiments were performed with ³²P‐labelled seston from the same lakes. Animals were also analysed for P‐content in their tissues at the end of these assays. 2. In general, assimilation efficiency was higher when animals fed on seston from shallow compared to deep lakes, and was significantly correlated with growth rates, suggesting that shallow lakes have the best food resources in terms of digestibility and P availability. 3. Results also showed that all cladoceran species responded similarly to the resource gradient, with lower growth rates in deep lakes and higher growth rates in shallow lakes, although the strength of response (sensitivity) was different among the species tested. 4. The cladoceran Moina micrura was the most sensitive species, and also displayed the highest P‐content and maximal growth rate, a pattern consistent with the growth rate hypothesis. 5. However, seston C : P ratio and growth rates in the different resources did not correlate with the animals’ P‐contents, showing an uncoupling between RNA‐phosphorus demands for growth and seston food quality. 6. In conclusion, our results support the idea that digestion resistance in algae is a major constraint to cladocerans in natural plankton communities.     

Seasonal and interannual variations in carbon dioxide exchange over a cropland in the North China Plain

In China, croplands account for a relatively large form of vegetation cover. Quantifying carbon dioxide exchange and understanding the environmental controls on carbon fluxes over croplands are critical in understanding regional carbon budgets and ecosystem behaviors. In this study, the net ecosystem exchange (NEE) at a winter wheat/summer maize rotation cropping site, representative of the main cropping system in the North China Plain, was continuously measured using the eddy covariance technique from 2005 to 2009. In order to interpret the abiotic factors regulating NEE, NEE was partitioned into gross primary production (GPP) and ecosystem respiration (R_eco). Daytime R_eco was extrapolated from the relationship between nighttime NEE and soil temperature under high turbulent conditions. GPP was then estimated by subtracting daytime NEE from the daytime estimates of R_eco. Results show that the seasonal patterns of the temperature responses of R_eco and light‐response parameters are closely related to the crop phenology. Daily R_eco was highly dependent on both daily GPP and air temperature. Interannual variability showed that GPP and R_eco were mainly controlled by temperature. Water availability also exerted a limit on R_eco. The annual NEE was ?585 and ?533 g C m^?2 for two seasons of 2006–2007 and 2007–2008, respectively, and the wheat field absorbed more carbon than the maize field. Thus, we concluded that this cropland was a strong carbon sink. However, when the grain harvest was taken into account, the wheat field was diminished into a weak carbon sink, whereas the maize field was converted into a weak carbon source. The observations showed that severe drought occurring during winter did not reduce wheat yield (or integrated NEE) when sufficient irrigation was carried out during spring.     

用RACE技术扩增并克隆牛BMP4基因3′端序列

RACE技术是一项扩增基因末端序列的新技术。该研究从牛BMP4基因出发,以牛软骨的RNA为模板,按照不同物种BMP4基因的相似性设计特异引物,运用PCR和RACE技术扩增并获得了特异片段,该片段经PCR、酶切和测序验证,证实所克隆序列为牛BMP4的3′端序列,包含有1170bp组成的开放读码框(ORF),编码389个氨基酸,3′非编码区121bp个核苷酸和poly(A)15。同源性分析结果表明,牛BMP4 cDNA最大开放读码框所推测的氨基酸序列与已知人、小鼠、大鼠、狗、羊和鸡等真核生物BMP4氨基酸序列进行比较,分别有94.5%、93.1%、91.9%、87.4%、94.2%、79%的同源性。这为克隆其他物种的BMP4基因提供了依据,同时牛骨形态发生蛋白的测序为我们更好的理解牛的生骨机理提供帮助。     

寒武纪凯里生物群在贵州镇远竹坪地区的发现

贵州东部镇远县竹坪地区付家冲寒武系凯里组中上部Oryctocephalus indicus带至Peronopsis taijiangensis带粉砂质泥岩、泥岩中新发现丰富的多门类化石组合,共计22属及3未定属种,分属海绵动物、节肢动物、腕足动物、软体动物、棘皮动物、腔肠动物,鳃曳动物、水母状动物及藻类9大门类,其中动...     

Effect of cholesterol on the membrane interaction of Modelin-5 isoforms

Modelin-5 isoforms were used to gain an insight into the effects of amidation on antimicrobial selectivity. When tested against Escherichia coli, amidation increased toxicity 10-fold (MIC = 31.25 μM) while showing limited increased hemolytic activity (2% lysis). Our results show that both the amidated and non-amidated peptides had a disordered structure in aqueous solution (<18% helical) and folded to form helices at the membrane interface (for example, >43% in the presence of DMPC). The stabilization of the helical structure by amidation has previously been shown to play a key role in increasing antibacterial efficacy. The presence of cholesterol in the membrane increases the packing density (C(s)(-1) values 25-33 mN m(-1)) and so prevents the peptide from forming stable association with the membrane, which is evidenced by the higher binding coefficient (K(d)) in the presence of cholesterol: 57.70 μM for Modelin-5-COOH and 35.64 μM for Modelin-5-CONH(2) compared to the presence of E. coli lipid extract (10 μM), which would prevent local concentration of the peptide at the bilayer interface as seen by reduction in monolayer interaction. This in turn would be predicted to inhibit activity.     

Influence of C-terminal amidation on the efficacy of modelin-5

To gain insight into the effects of amidation on the mechanism of membrane interaction, we studied two peptides modelin-5-COOH and modelin-5-CONH(2) and found they exhibit high surface activities (23.2 and 27.1 mN/m, respectively). When they were tested against Escherichia coli, amidation was seen to increase efficacy approximately 10-fold. Our results demonstrated that both peptides adopted low levels of α-helix in solution (<20%); however, in the presence of E. coli lipid extract, modelin-5-CONH(2) had a greater propensity (69%) than modelin-5-COOH (32%) to generate α-helical structure. The binding coefficient for both peptides was ～10 μM, and the Hill coefficient approximated 1, suggesting that for both peptides the interactions with E. coli membranes were monomeric and comparable in strength. The peptides showed a clear preference for anionic lipid, with monolayer data showing that enhanced levels of helicity were associated with a greater pressure change (～6 mN/m). Use of fluorescein-phosphatidylethanolamine showed the amidated version was able to generate greater levels of membrane disruption, which was confirmed by thermodynamic analysis. The data would imply that both peptides are able to initially bind to bilayer structures, but upon binding, the amidation stabilizes helix formation. This would be expected to help overcome a key rate-limiting step and generate higher local concentrations of peptide at the bilayer interface, which in turn would be predicted to increase efficacy.     

A specimen of Curculioninae (Curculionidae,Coleoptera) from the Lower Cretaceous,Araripe Basin,north‐eastern Brazil

Abstract: A specimen of Curculionidae (Curculioninae) is described as Arariperhinus monnei gen. et sp. nov. The specimen is preserved on a laminated limestone sample of the Crato Formation (Santana Group), Lower Cretaceous (Aptian–Albian), and was collected from a quarry near Nova Olinda, Chapada do Araripe, State of Ceará, Brazil. The genus is placed in the subfamily Curculioninae because of its strongly convex body and relatively slender rostrum, but mainly by its rounded eyes and lack of a prosternal sulcus and tibial spurs. The very prominent eyes in lateral view, a cylindrical rostrum and a straight posterior margin of ventrite II are strong indications that this fossil belongs to the tribe Anthonomini. However, the claws, which would resolve the exact placement of this fossil, are poorly preserved. Arariperhinus monnei gen. et sp. nov. is distinguishable by the combination of several characters and the first record of the family Curculionidae in the Santana Group; it is the oldest record of a member of the subfamily Curculioninae.     

Calpains: targets of cataract prevention?

There is emerging evidence to suggest that the unregulated Ca(2+)-mediated proteolysis of essential lens proteins by calpains might be a major contributor to some forms of cataract in both animals and humans. Moreover, recently solved calpain structures have revealed molecular-level details of the activation mechanism used by these proteases, enabling the structure-based design of potent calpain inhibitors with the potential to act as anti-cataract agents. These agents offer the first real hope of an urgently needed alternative to the surgical treatment of at least some forms of cataract and relief from a life-depreciating condition on a global scale.