Plant extracts and their components as potential control agents against human head lice

The head lice, Pediculus humanus capitis (Phthiraptera:Pediculidae), is an obligate ectoparasite of humans that causes pediculosis capitis, a nuisance for millions of people worldwide, with high prevalence in children. Pediculosis capitis has been treated by methods that include the physical remotion of lice, various domestic treatments and conventional insecticides. None of these methods render complete protection, and there is clear evidence for the evolution of resistance and cross-resistance to conventional insecticides. Non-toxic alternative options are hence needed for head lice treatment and/or prevention, and natural products from plants, especially essential oils (EOs), are good candidates for safer control agents that may provide good anti-lice activity and low levels of evolved resistance. A few EOs have been tested as repellents with promissory results, although often in vitro tests and clinical trials produce contradictory results. A handful of fixed extracts and several EOs and their individual components have also been tested as contact pediculicides or fumigants. The studies have focused mainly on plant families characterized for the production of EOs. While many EOs and individual compounds showed pediculicide activity, comparing results is difficult due to the diverse bioassay methodologies. Studies of anti-lice activity of individual EO components provide the basis for preliminary conclusions of structure–activity relationships, although no clear patterns can yet be drawn. We here attempt to provide a concise compilation of the available information on anti-lice activity of plant extracts and plant-derived compounds, which we hope may be of help for future developments in this area.

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Liquid medium and liquid overlays improve embryogenic tissue initiation in conifers

Somatic embryogenesis (SE) is expected to play an important role in increasing productivity, sustainability, and uniformity of future US forests. For commercial use, SE technology must work with a variety of genetically diverse trees. Initiation in loblolly pine (Pinus taeda L.), the main commercial US forest species, is often recalcitrant for desirable genotypes. Liquid initiation medium with no or low gelling agent or placement of the explant on gelled medium followed later by a liquid medium overlay during the initiation process increased initiation for loblolly pine and Norway spruce (Picea abies). Loblolly pine liquid medium required reduction of NAA from 2 mg/l in gelled medium to 0.3 mg/l in liquid medium. Once the NAA concentration was adjusted, loblolly pine initiation occurred in liquid medium with fully immersed megagametophytes, explants supported at the liquid medium surface, or on gelled medium overlaid with liquid medium. Liquid overlays (0.25 ml) consisting of medium with NAA reduced to 0.3 mg/l, 9 mg/l ABA and no gelling agent applied to explants on 2 ml of gelled medium provided excellent initiation results. Greatest initiation percentages occurred when the liquid overlay was applied 14 days after placement of the megagametophyte on gelled medium. Initiation increases ranged from +8.5% with high-value cross-pollinated seed sources to +6.5 to +9.9% with open-pollinated and often recalcitrant seed sources. Liquid medium addition allows rapid replenishment of nutrients and adjustment or change of pH, hormones, or other parameters without disturbing the tissue.     

Substrate specificity of nonribosomal peptide synthetase modules responsible for the biosynthesis of the oligopeptide moiety of cephabacin in Lysobacter lactamgenus

Lysobacter lactamgenus produces cephabacins, a class of beta-lactam antibiotics which have an oligopeptide moiety attached to the cephem ring at the C-3 position. The nonribosomal peptide synthetase (NRPS) system, which comprises four distinct modules, is required for the biosynthesis of this short oligopeptide, when one takes the chemical structure of these antibiotics into consideration. The cpbI gene, which has been identified in a region upstream of the pcbAB gene, encodes the NRPS - polyketide synthase hybrid complex, where NRPS is composed of three modules, while the cpbK gene -- which has been reported as being upstream of cpbI-- comprises a single NRPS module. An in silico protein analysis was able to partially reveal the specificity of each module. The four recombinant adenylation (A) domains from each NRPS module were heterologously expressed in Escherichia coli and purified. Biochemical data from ATP-PPi exchange assays indicated that L-arginine was an effective substrate for the A1 domain, while the A2, A3 and A4 domains activated L-alanine. These findings are in an agreement with the known chemical structure of cephabacins, as well as with the anticipated substrate specificity of the NRPS modules in CpbI and CpbK, which are involved in the assembly of the tetrapeptide at the C-3 position.     

Genetically Modified Pigs as Organ Donors for Xenotransplantation

The growing shortage of available organs is a major problem in transplantology. Thus, new and alternative sources of organs need to be found. One promising solution could be xenotransplantation, i.e., the use of animal cells, tissues and organs. The domestic pig is the optimum donor for such transplants. However, xenogeneic transplantation from pigs to humans involves high immune incompatibility and a complex rejection process. The rapid development of genetic engineering techniques enables genome modifications in pigs that reduce the cross-species immune barrier.     

Corrections and additions to the Dumontiidae Santos-Flores &; Dodson, 2003 (Crustacea: Branchiopoda: Anomopoda), and implications for anomopod phylogeny

The presumed sixth limb of Dumontia Santos-Flores & Dodson, 2003 is shown to correspond to the inner part of the fifth limb. Comparison of the latter structure within the order increases the similarity between the Dumontiidae and the Daphniidae (plus Moinidae), but important similarities with the Radopoda remain. The relationship between a ‘‘daphniid line’’ and radopods needs further attention. Handling editor: K. Martens     

Covalent attachment of synthetic DNA to self-assembled monolayer films.

The covalent attachment of thiol-modified DNA oligomers; to self-assembled monolayer silane films on fused silica and oxidized silicon substrates is described. A heterobifunctional crosslinking molecule bearing both thiol- and amino-reactive moieties was used to tether a DNA oligomer (modified at its terminus with a thiol group) to an aminosilane film formed on silica surfaces. A variety of aminosilanes, crosslinkers and treatment conditions have been tested to identify optimal conditions for DNA immobilization using this approach. The DNA films which result have been characterized using UV spectroscopy, water contact angle measurement, radiolabeling and hybridization methods.     

Variation in bean morphology and biochemical composition measured in different genetic groups of arabica coffee (<Emphasis Type="Italic">Coffea arabica</Emphasis> L.)

The narrow genetic base of commercial arabica resulting from intensive selection for quality during domestication and self-pollination has been well documented, raising the need for new diverse germplasm sources. Beans of 232 diverse arabica coffee accessions originating from 27 countries were harvested from the germplasm collection at CATIE, Costa Rica. Substantial variation was observed for bean morphology including 100 bean weight, bean length, width, thickness and bulk density. Non-volatiles including caffeine and trigonelline were analysed and showed larger variation in range than has previously been reported. Results of targeted analysis of 18 volatiles from 35 accessions also showed significant variation, with coefficients of variation from 140% for 4-vinylguaiacol to 62% for geraniol. There were strong correlations between some volatile compounds, suggesting that representative volatiles used in selection would save analytical costs. However, no strong correlation was found between bean morphology and the levels of non-volatile or volatile compounds, implying that it is difficult to select for low or high composition of these compounds based on bean physical characteristics. Utilizing the large variation observed for bean morphology and biochemical traits, it should be possible to select for desirable combinations of traits in arabica coffee breeding.