Retroviruses can establish filopodial bridges for efficient cell-to-cell transmission

The spread of retroviruses between cells is estimated to be 2-3 orders of magnitude more efficient when cells can physically interact with each other. The underlying mechanism is largely unknown, but transfer is believed to occur through large-surface interfaces, called virological or infectious synapses. Here, we report the direct visualization of cell-to-cell transmission of retroviruses in living cells. Our results reveal a mechanism of virus transport from infected to non-infected cells, involving thin filopodial bridges. These filopodia originate from non-infected cells and interact, through their tips, with infected cells. A strong association of the viral envelope glycoprotein (Env) in an infected cell with the receptor molecules in a target cell generates a stable bridge. Viruses then move along the outer surface of the filopodial bridge toward the target cell. Our data suggest that retroviruses spread by exploiting an inherent ability of filopodia to transport ligands from cell to cell.     

Stepped water activity control for efficient enzymatic interesterification

The benefits of controlling water activity, a _w, during enzymatically catalysed synthesis reactions, such as reverse-hydrolytic reactions promoted by lipases, are now well recognized. Numerous techniques for controlling a _w in the laboratory and their implementation in continuous reactors have been discussed in the published literature. However, in enzymatic interesterification reactions, such as acidolysis and transesterification, it is not appropriate merely to maintain the a _w of the reaction system at one value since the two stages of the reaction, namely the cleavage of the original acyl bond and the formation of a new one, are best carried out at different levels of water activity – the former at a high a _w and the latter at a lower one. The use of a continuous packed-bed hollow-fibre reactor has been described in this article for carrying out solvent-free acidolysis of ethyl laurate with octanoic acid with in situ a _w control, using air that has been pre-equilibrated with saturated salt solutions to the desired a _w. At a single optimum (a _w = 0.54), the highest steady-state conversion to ethyl octanoate was 32%. However, it is possible to obtain a steady-state conversion of 46% by operating the reactor with a step change in the water activity, from an initial value of unity to 0.23. Received: 10 February 1998 / Received revision: 2 June 1998 / Accepted: 7 June 1998     

Engineering hypervirulence in a mycoherbicidal fungus for efficient weed control

Agents proposed for biocontrol of major weeds in arable row-crop agriculture have not met expectations because an evolutionary balance has developed between microorganism and weed, even when the mycoherbicide is used inundatively at very high levels (>10(4)spores/cm<(2)). Sufficient virulence can be achieved by transferring genes to the microorganism, tipping the evolutionary balance. Virulence was increased ninefold and was more rapidly effected; furthermore, the requirement for a long duration at high humidity was decreased by introducing NEP1 encoding a phytotoxic protein, to an Abutilon theophrasti-specific, weakly mycoherbicidal strain of Colletotrichum coccodes. The parent strain was at best infective on juvenile cotyledons of this intransigent weed. The transgenic strain was lethal through the three-leaf stage, a sufficient time window to control this asynchronously germinating weed. Strategies of coupling virulence genes with fail-safe mechanisms to prevent spread (due to broadened host range) and to mitigate transgene introgression into crop pathogens could be very useful in the biocontrol of major weeds in row crops.     

Bioengineering and management for efficient phosphorus utilization in crops and pastures

Strategies for improving efficient phosphorus utilization in crops and pastures: 1. Conventional and marker assisted selection breeding; 2. Transgenic modification; 3. Optimization of P fertilization and cultivation management.

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Highlights? Phosphorus efficiency is improved via conventional and marker assisted selection breeding. ? The vital genes are applied to improve P efficiency through biotech. ? Optimization of P fertilization and cultivation management improves P efficiency. ? It is vital to integrate bioengineering, P fertilization and cultivation management.     

Microarrays of peptides elevated on the protein layer for efficient protein kinase assay

Peptide microarrays can be used for the high-throughput analysis of protein-peptide interactions. However, current peptide microarrays are rather costly to make and require cumbersome steps of introducing novel polymeric surfaces and/or chemical derivatization of peptides. Here, we report a novel method for manufacturing peptide microarrays by elevating the peptide on the layer of protein by a fusion protein approach. Using two protein kinases and their peptide substrates as examples, we show that elevating peptides on the layer of protein allows sensitive, specific, and efficient detection of peptide-protein interactions without the need for complicated chemical modification of solid supports and peptides. It was found that kinase activity could be detected with as low as 0.09 fmol of kemptide, which is about 1000-fold more sensitive than the 0.1 pmol obtained with other microarray systems. Furthermore, peptides can be produced as fusion proteins by fermentation of recombinant Escherichia coli and thus the expensive peptide synthesis process can be avoided. Therefore, this new strategy will not only be useful in high-throughput and cost-effective screening of kinase substrate peptides but also be generally applicable in studying various protein-peptide interactions.     

An efficient method for the in vitro management of multiple garlic accessions

Summary A simple protocol for garlic in vitro management is described. It comprises a single medium for all developmental stages and genotypes tested, and the use of immature bulbs as source of axillary buds. Although genetic variability exists among the different accessions tested, for both the multiplication rate and bulblet size, acceptable values of multiplication were reached for all the accessions, and values of bulb formation approached 100% in the shoots produced.     

Orientational control is an efficient control mechanism for phase switching in the E. coli fim system

The fim system in E. coli controls the expression of type-1 fimbriae. These are hair-like structures that can be used to attach to host cells. Fimbriation is controlled by a mechanism called "orientational control." We present two families of models for orientational control to understand the details of how it works. We find that the main benefits of orientational control are that (i) it allows rapid adjustment of fimbriation levels in response to a change of environmental conditions while (ii) keeping the overall frequencies with which a cell switches between the fimbriate state and the afimbriate state low. The main reason for the efficiency of orientational control in regulation of fimbriation levels is that it keeps the system far from its steady state.     

Evidence for a noradrenergic transmission in the control of parturition in the rat

6-Hydroxydopamine, when injected at 14:00 h on Days 21 and 22 of pregnancy in the rat (2 X 50 mg/kg), markedly decreased plasma and uterine noradrenaline concentrations (-60% and -82% respectively; P less than 0.001). As a consequence of this treatment, there was severe disturbance in the distribution pattern of parturitions: 61% of rats had suppressed parturition and 31% of rats displayed a lengthened or interrupted labour. A bolus dose of prazosin (3 mg/kg) administered at 12:00 h on Day 22 completely blocked the normal process of parturition throughout the next 6 h, a result which is compatible with the half-life of the drug (2.9 +/- 0.8 h). Administration of phentolamine (3 mg/kg) at term induced a significant decrease of uterine activity (frequency X duration of bursts of spike potentials) as revealed by electromyographic recordings in vivo. These results suggest that noradrenaline released from sympathetic nerve terminals interacts with alpha-adrenoceptors located post-synaptically to improve the overall excitability of the myometrium at the onset of labour.     

Thin cell layer technology for induced response and control of rhizogenesis in chrysanthemum

Chrysanthemum (Dendranthema Xgrandiflora Ramat. Kitamura) stem transverse thin celllayers (tTCLs) were used to obtain defined morphogenic programs with selectedplant growth regulators. A rhizogenic pathway could be manipulated invitro by the application of a single auxin (2,4-D, NAA, IBA or IAA,in increasing order of rhizogenic response), or by the addition of coconutwater, with light or darkness playing a significant role. The addition of TIBAeliminated the rhizogenic capacity of all the auxins tested, but not that ofcoconut water, while the addition of activated charcoal was inhibitory. Theabsence of sucrose resulted in a limited rhizogenic response. Results clearlyindicate the importance of auxins, media additives and light in the activationof a rhizogenic program in chrysanthemum tTCLs. Due to their restricted size andmedium-dependant nature, the capacity to control rhizogenesis and/ororganogenesis in chrysanthemum (and indeed any plant species) by TCLs hasfar-reaching consequences and applications in the floricultural andpharmaceutical sectors. Since all factors (exogenously-applied hormones andother growth-stimulating or growth-inhibiting substances, light, temperature,humidity and other environmental cues) may be strictly controlled invitro, TCL technology allows for the establishment of protocols aimedat chrysanthemum flower improvement through genetic engineering, the success ofwhich lies in its first step i.e. programmable morphogenesis and regeneration.     

生境管理——保护性生物防治的发展方向

生境管理是近年来保护性生物防治的重要研究方向,也是利用农业景观格局进行生物防治的重要策略。生境管理是指从农田景观的角度,在大时空尺度范围内进行多种作物与非作物生境的设计与布局,创造有利于天敌的环境条件,抑制害虫种群发生,达到减小环境污染、增强农业生态系统的控害保益功能,最终实现害虫种群控制的可持续性。景观尺度下的生境管理不仅强调单一农田生物控害作用,而是以多生境农业景观整体布局为指导,探索各种生境功能的整合利用,以发挥各种生境最大的生物控害潜能,为实现多目标生态服务价值管理提供重要的理论基础和现实依据。本文系统地总结了生境管理的研究内容与实现途径,论述了农业景观格局与过程对害虫种群控制的机理,并对作为保护性生物防治发展方向的生境管理研究趋势进行了展望。     

Lack of tree layer control on herb layer characteristics in a subtropical forest,China

Question: Knowledge of the interaction between understorey herb and overstorey tree layer diversity is mostly restricted to temperate forests. How do tree layer diversity and environmental variables affect herb layer attributes in subtropical forests and do these relationships change in the course of succession? Do abundance and diversity of woody saplings within the herb layer shift during succession? Location: Subtropical broad‐leaved forests in southeast China (29°8′18″‐29°17′29″N, 118°2′14″118°11′12″E). Methods: A full inventory of the herb layer including all plants below 1‐m height was done in 27 plots (10 × 10 m) from five successional stages (<20, <40, <60, <80 and ≥80 yr). We quantified the contribution of different life forms (herbaceous, woody and climber species) to herb layer diversity and productivity and analysed effects of environmental variables and tree layer diversity on these attributes. Results: Herb layer composition followed a successional gradient, as revealed by non‐metric multidimensional scaling (NMDS), but diversity was not correlated to the successional gradient. There was no correlation of diversity across layers. Herb layer productivity was neither affected by tree layer diversity nor by herb layer diversity. Although abundance of woody species in the herb layer decreased significantly during succession, woody species contributed extraordinarily to herb layer species diversity in all successional stages. All environmental factors considered had little impact on herb layer attributes. Conclusions: The subtropical forest investigated displays an immense richness of woody species in the herb layer while herbaceous species are less prominent. Species composition of the herb layer shows a clear successional pattern, however, the presence or absence of certain species appears to be random.