Sugar transport together with environmental conditions controls time lags between xylem and stem diameter changes

In the present study the seasonal patterns of time lags between diurnal xylem and whole stem diameter variations at the top and at the base of two Scots pine trees (Pinus sylvestris L.) were compared. The diameter variations were measured during the summers of 2001 and 2002. Time lags were determined using the cross‐correlation method. The lags were found to vary in time according to the different stages of growth. At the top the xylem lagged behind the whole stem between the beginning of stem growth and the end of shoot growth in both years. In 2001 the time lags at the base showed a similar behaviour during stem growth. That kind of seasonal pattern of the time lags would result from the changes in the sink strength due to changing growth rate at different parts of the tree and the differences in the annual rhythm of growth and water availability in the soil (based on precipitation measurements) between the years 2001 and 2002 were reflected in the patterns. The time lags of shrinking and swelling periods during high and low photosynthetic activity (measured using a shoot chamber) were also compared. It was found, for example, that in 2001 in the middle of the growing season at the top of the tree the whole stem lagged on average 15 min more behind the xylem on the days of high photosynthetic activity than on the days of low or moderate. These results show for the first time that the transportation of carbohydrates and variable sink activity could be detected during the growing season in field conditions using stem and xylem diameter variation measurements. Furthermore, these results provide evidence of the pressure gradient‐driven flow also in the phloem of gymnosperms.     

SOUND PRODUCTION IN THE LARVAE OF GEOTRUPES SPINIGER (MARSHAM) (COLEOPTERA: GEOTRUPIDAE)

ABSTRACT

This paper focuses on sound production in the larvae of Geotrupes spiniger (Marsham) (Coleoptera: Geotrupidae). A single stridulatory apparatus was identified and then analysed from a structural point of view. Sound was studied using spectography and results included a quantitative analysis with characterizing physical parameters. Results highlight the need to study stridulation in Geotrupidae more in detail, to improve our understanding of its evolutionary and biological meaning.     

CorTectorTM SX100：一款桌面式荧光相关光谱仪的原理和应用

荧光相关光谱检测技术具有超灵敏(单分子)、快速(数秒至数分钟)和多功能(检测分子浓度、大小和相互作用)等技术优点,且无需反应物分离,因此有潜力成为一种新型均相、高敏荧光免疫检测技术,适用于在溶液中或单个活细胞内检测生物分子特性．本文首先介绍荧光相关光谱检测技术的原理和研究进展,然后结合项目团队自主研发的目前全球唯一一款可靠、易使用的桌面式荧光相关光谱仪,进一步探讨荧光相关光谱检测技术的具体实现和潜在应用．     

Monitoring the caspase cascade in single apoptotic cells using a three-color fluorescent protein substrate

Fluorescence cross-correlation spectroscopy (FCCS) reveals information about the spatiotemporal coincidence of two spectrally well-defined fluorescent molecules in a small observation area at the level of single-molecule sensitivity. To simultaneously evaluate the activities of caspase-3 and caspase-9, we constructed a chimeral protein that consisted of tandemly fused enhanced cyan fluorescent protein (ECFP), monomeric red fluorescent protein (mCherry) and monomeric yellow fluorescent protein (Venus). In HeLa cell lysates, a combination of tumor necrosis factor-α (TNF-α)- and cycloheximide (CHX-)-induced apoptosis was monitored. In this, decreases of cross-correlation amplitudes were observed between ECFP and mCherry and between mCherry and Venus. Moreover, time-dependent monitoring of single cells revealed decreases in the cross-correlation amplitudes between ECFP and mCherry and between mCherry and Venus before morphologic changes were observed by laser scanning fluorescence microscopy (LSM). Thus, our method could predict the fate of the cell in the early apoptotic stage.     

Ecology of Biomphalaria (Gastropoda: Planorbidae) in Lake Albert, Western Uganda: snail distributions, infection with schistosomes and temporal associations with environmental dynamics

In Lake Albert, an ecological study was conducted, between June 2000 and May 2003, which assessed snail population dynamics, parasite infection patterns and interplay of environmental factors upon Biomphalaria. Monthly sampling surveys were conducted at 29 sites monitoring populations of Biomphalaria stanleyi and Biomphalaria sudanica. Altogether, a total of 21,715 B. stanleyi and 8452 B. sudanica were collected during the period. Both species could be found infected with Schistosoma mansoni although infection prevalence was significantly higher (p < 0.01**) in B. stanleyi (4.4%) than in B. sudanica (3.5%). Each species occupied slightly different aquatic niches with B. stanleyi preferring deeper water habitats whilst B. sudanica was found along the shoreline in shallower water. B. stanleyi was more widely distributed among the sampling locations (19 sites) than B. sudanica (10 sites). Of the four villages included in the study area, snails from sites near Piida and Bugoigo villages had the highest schistosome infection rates, presumably attributable to the closer proximity of people with intestinal schistosomiasis. After inspection of cross-correlation plots which identified most suitable time lags, snail density dynamics could be associated with seasonal variations inclusive of: air temperature, rainfall, lake level, water temperature, water conductivity and water pH. These temporal observations better reveal the relationship between snail populations and environmental factors, providing important information concerning the relative roles of B. stanleyi and B. sudanica in transmission of S. mansoni and development of integrated strategies for disease control around Lake Albert.     

Revealing binding selectivity of ligands toward murine double minute 2 and murine double minute X based on molecular dynamics simulations and binding free energy calculations

Abstract

It is well known that the interactions of p53 with murine double minute 2 and murine double minute X, namely MDM2 and MDMX, have been significant targets of efficient anti-cancer drug design. In this study, molecular dynamics (MD) simulations, principal component (PC) analysis and binding free energy calculations are combined to recognize binding selectivity of three ligands to MDM2 and MDMX. The binding free energies were estimated by using molecular mechanics generalized Born surface area (MM-GBSA) method and the obtained results display that the increase in the binding enthalpy of three ligands to MDM2 relative to MDMX mainly drives the binding selectivity of them toward MDM2 and MDMX. The information obtained from PC analysis shows that the associations of ligands exert important impacts on internal dynamics of MDM2 and MDMX. Meanwhile, the calculations of residue-based free energy decomposition not only identify the hot interaction spots of ligands with MDM2 and MDMX, but also show the residues (L54, M53), (Y67, Y66), (V93, V92), (H96, P95), (I99, I98) and (Y100, Y99) in (MDM2, MDMX) are responsible for most contributions to the binding selectivity of three ligands toward MDM2 and MDMX. It is believed that this work can provide useful information for design of highly selective and dual inhibitors targeting MDM2 and MDMX.

Communicated by Ramaswamy H. Sarma     

Conformational Plasticity of Hepatitis C Virus Core Protein Enables RNA-Induced Formation of Nucleocapsid-like Particles

Many of the unanswered questions associated with hepatitis C virus assembly are related to the core protein (HCVcp), which forms an oligomeric nucleocapsid encompassing the viral genome. The structural properties of HCVcp have been difficult to quantify, at least in part because it is an intrinsically disordered protein. We have used single-molecule Förster Resonance Energy Transfer techniques to study the conformational dimensions and dynamics of the HCVcp nucleocapsid domain (HCVncd) at various stages during the RNA-induced formation of nucleocapsid-like particles. Our results indicate that HCVncd is a typical intrinsically disordered protein. When it forms small ribonucleoprotein complexes with various RNA hairpins from the 3′ end of the HCV genome, it compacts but remains intrinsically disordered and conformationally dynamic. Above a critical RNA concentration, these ribonucleoprotein complexes rapidly and cooperatively assemble into large nucleocapsid-like particles, wherein the individual HCVncd subunits become substantially more extended.