Construction of a linkage map of the Rennell Island Tall coconut type (Cocos nucifera L.) and QTL analysis for yield characters.

AFLP and SSR DNA markers were used to construct a linkage map in the coconut (Cocos nucifera L.; 2n = 32) type Rennell Island Tall (RIT). A total of 227 markers were arranged into 16 linkage groups. The total genome length corresponded to 1971 cM for the RIT map, with 5-23 markers per linkage group. QTL analysis for yield characters in two consecutive sampling periods identified nine loci. Three and two QTLs were detected for number of bunches and one and three QTLs for number of nuts. The correlation of trait values between characters and evaluation periods is partially reflected in identical QTLs. The QTLs represent characters that are important in coconut breeding. The cosegregation of markers with these QTLs provides an opportunity for marker-assisted selection in coconut breeding programmes.     

Effects of defoliation intensity on soil food-web properties in an experimental grassland community

We established a greenhouse experiment based on replicated mini‐ecosystems to evaluate the effects of defoliation intensity on soil food‐web properties in grasslands. Plant communities, composed of white clover (Trifolium repens), perennial ryegrass (Lolium perenne) and plantain (Plantago lanceolata) with well‐established root and shoot systems, were subjected to five defoliation intensity treatments: no trimming (defoliation intensity 0, or DI 0), and trimming of all plant material to 35 cm (DI 1), 25 cm (DI 2), 15 cm (DI 3) and 10 cm (DI 4) above soil surface every second week for 14 weeks. Intensification of defoliation reduced shoot production and standing shoot and root mass of plant communities but increased their root to shoot ratio. Soil microbial activity and biomass decreased with intensification of defoliation. Concentrations of NO₃–N in soil steadily increased with intensifying defoliation, whereas NH₄–N concentrations did not vary between treatments. Numbers of microbi‐detritivorous enchytraeids, bacterial‐feeding rotifers and bacterial‐feeding nematodes steadily increased with intensifying defoliation, while the abundance of fungal‐feeding nematodes was significantly enhanced only in DI 3 and DI 4 relative to DI 0. The abundance of herbivorous nematodes per unit soil mass was lower in DI 3 and DI 4 than in DI 0, DI 1 and DI 2, but when calculated per unit root mass, their abundance tended to increase with defoliation intensity. The abundance of omnivorous and predatory nematodes appeared to be highest in the most intensely defoliated systems. The ratio of abundance of fungal‐feeding nematodes to that of bacterial‐feeding nematodes was not significantly affected by defoliation intensity. The results infer that defoliation intensity may significantly alter the structure of soil food webs in grasslands, and that defoliation per se is able to induce patterns observed in grazing studies in the field. The results did not support hypotheses that defoliation per se would cause a shift between the bacterial‐based and fungal‐based energy channels in the decomposer food web, or that herbivore and detritivore densities in soil would be highest under intermediate defoliation. Furthermore, our data for microbes and microbial feeders implies that the effects of defoliation intensity on soil food‐web structure may depend on the duration of defoliation and are therefore likely to be dynamic rather than constant in nature.     

The Mycobacterium marinum G13 promoter is a strong sigma 70-like promoter that is expressed in Escherichia coli and mycobacteria species

A Mycobacterium marinum promoter, designated G13, was isolated from a promoter-trap library as a constitutive producer of the mutant green fluorescent protein. Sequence analysis, primer extension analysis, and computer promoter prediction analysis indicate that the G13 promoter is very similar to Escherichia coli consensus sigma 70 promoters. Expression of the green fluorescent protein from the G13 promoter in M. marinum is, however, up to 40 times higher than that seen from the mycobacterial hsp60 promoter during exponential growth. Further, expression from this promoter does not appear to affect the growth of the organism in culture media or in macrophages. The strong expression of the G13 promoter allows it to be developed as a useful molecular tool for high level expression of markers in vitro.     

Automated system for capture and detection of nucleic acids.

A fully automated nucleic acid analysis system is described, which offers positive sample identification, improved sensitivity and reduced user interaction compared to conventional techniques. The system relies on the sequence-specific capture of DNA onto solid-phase particles, confirming product identity without the problems of interpretation and lack of sequence information inherent in gel-based analyses. The system can be used for sequence confirmation, mutation analysis and semiquantitative detection of PCR products.     

微塑料对湖泊生态系统初级生产者的影响

塑料的广泛应用导致大量微塑料进入环境,尤其是水环境,从而产生环境风险。浮游植物等自养生物是湖泊系统的主要初级生产者,是湖泊食物链的关键组成部分,为食物链的上游提供能量和物质基础。同时,浮游植物也是对微塑料响应最敏感的类群。了解湖泊浮游植物等初级生产者对微塑料的响应是探究微塑料对湖泊生态系统功能影响的重要基础。总结了全球湖泊生态系统微塑料的丰度、类型、尺寸、来源等分布特征,系统分析了微塑料暴露对浮游植物等初级生产者细胞结构、基因表达和生长,以及对浮游植物叶绿素a含量、光合活性的影响,并总结了其中的影响机制。总体而言,微塑料会降低初级生产者的叶绿素a含量,剂量越高、尺寸越小,这种抑制作用越强烈;同时,微塑料也会作用于初级生产者,造成细胞膜损伤、DNA损伤,调控其相关功能基因表达,抑制其生长和光合活性等。然而,湖泊生态系统微塑料的实际检出浓度远低于室内暴露实验中的添加剂量,微塑料结构和组分也更为复杂,野外观测结果与室内培养实验之间还不能建立直接的对应关系。因此,未来的相关研究应集中在如何有效联系野外观测结果与室内培养实验结果,进一步聚焦建立可靠的、可应用推广的微塑料浓度与初级生产者之间的剂量-效应关系模型,探究微塑料对湖泊初级生产者的作用机制,为刻画微塑料对湖泊生态系统初级生产者及其功能的作用机制提供科学支撑。     

DNA diagnosis of human leishmaniasis

Early identification of the causal agent of human leishmaniasis is difficult even in a well-equipped hospital. This makes early treatment of cases more difficult, and also adds to the problem of accurately assessing the prevalence and incidence of the disease. Incrimination of vector species of sandfies and reservoir hosts is also complicated by difficulties in detecting and identifying the infective organisms. Although the importance of leishmantasis is now well-recognized, improved methods of diagnosis have been much in demand (Box 1). In this article. Douglas Barker reviews progress in developing diagnostic DNA probes for the parasites, that are suitable for use even in field areas.     

Sequential gel electrophoretic analysis of esterase-2 in two populations of Drosophila buzzatii

Sequential electrophoresis, using three different buffer systems on cellulose acetate gels, was used to characterize the allelic variation for esterase-2 in two populations of D. buzzatii in Australia that are separated by 550 km. Twenty-five alleles were detected, of which nine were unique to one population, eight unique to the other, and only eight were common to both populations. Allele frequencies within each population were significantly different between the two major chromosome sequences (standard and j inversion), and for each chromosome sequence allele frequencies were significantly different between populations. Observed allelic frequency distributions were not significantly different from those predicted for selective neutrality using the homozygosity test statistic. However, estimates of the effective sizes of the populations derived from their observed differentiation, together with the history of the species in Australia, provide support for some form of balancing selection affecting at least some of the alleles.     

Heparin and its derivatives bind to HIV-1 recombinant envelope glycoproteins, rather than to recombinant HIV-1 receptor, CD4

We have employed a direct radiolabel binding assay to investigate the interaction between3H-heparin and recombinant envelope glycoproteins, rgp120s, derived from several different isolates of HIV-1. Comparable dose-dependent binding is exhibited by rgp120s from isolates IIIB, GB8, MN and SF-2. Under identical experimental conditions the binding of3H- heparin to a recombinant soluble form of the cellular receptor for gp120, CD4, is negligible. The binding of3H-heparin to rgp120 is competed for by excess unlabeled heparin and certain other, but not all, glycosaminoglycan and chemically modified heparins. Of a range of such polysaccharides tested, ability to compete with3H-heparin for binding was strictly correlated with inhibition of HIV-1 replication in vitro. Those possessing potent anti-HIV-1 activity were effective competitors, whereas those having no or little anti-HIV-1 activity were poor competitors. Scatchard analysis indicates that the K d of the interaction between heparin and rgp120 is 10 nM. Binding studies conducted in increasing salt concentrations confirm that the interaction is ionic in nature. Synthetic 33-35 amino acid peptides based on the sequence of the V3 loop of gp120 also bind to heparin with high affinity. V3 loop peptides that are cyclized due to terminal cysteine residues show more selective binding than their uncyclized counterparts. Overall, these data demonstrate further that heparin exerts its anti-HIV-1 activity by binding to the envelope glycoprotein of HIV-1, rather than its cellular receptor, CD4. This study confirms that the V3 loop of gp120 is the site at which heparin exerts its anti- HIV-1 activity. Moreover, it reveals that high affinity binding to heparin is shared by all four rgp120s examined, despite amino acid substitutions within the V3 loop.