Effects of starvation and - or -alanine administration on the free - and -alanine levels in the muscle and hepatopancreas of the crayfish, Procambarus clarkii

Changes of - and -alanine and other free amino acids were examined in muscle and hepatopancreas of the crayfish Procambarus clarkii before and after a 1-month starvation in freshwater, 50% seawater, and seawater. Total free amino acids and - and -alanine in both tissues decreased during starvation. The largest decrease was found in the animals starved in freshwater. In 50% seawater and full-strength seawater, the ratio of -alanine to total alanine increased in both tissues, although the level was reduced a little. A large dose of -alanine administered into the tail muscle of freshwater crayfish was converted to -alanine and -alanine returned to the control level within a week. A large amount of -alanine was transported from muscle to hepatopancreas. -Alanine injected into freshwater crayfish was converted to -alanine, but was not transported to the hepatopancreas. In the case of -alanine injection into the muscle of crayfish acclimated to 50% seawater, large amounts of - and -alanine were maintained in the muscle during the experimental period of 4 days. These data indicate that -alanine is metabolized actively in crayfish tissues and accumulated as an important osmolyte during osmotic stress.     

Microcalorimetric studies of the interactions between cytochromes c and c1 and of their interactions with phospholipids

Thermotropic properties of purified cytochrome c₁ and cytochrome c have been studied by differential scanning calorimetry under various conditions. Both cytochromes exhibit a single endothermodenaturation peak in the differential scanning calorimetric thermogram. Thermodenaturation temperatures are ionic strength, pH, and redox state dependent. The ferrocytochromes are more stable toward thermodenaturation than the ferricytochromes. The enthalpy changes of thermodenaturation of ferro- and ferricytochrome c₁ are markedly dependent on the ionic strength of the solution. The effect of the ionic strength of solution on the enthalpy change of thermodenaturation of cytochrome c is rather insignificant. The formation of a complex between cytochromes c and c₁ at lower ionic strength causes a significant destabilization of the former and a slight stabilization of the latter. The destabilization of cytochrome c upon mixing with cytochrome c₁ was also observed at high ionic strength, under which conditions no stable complex was detected by physical separation. This suggests formation of a transient complex between these two cytochromes. When cytochrome c was complexed with phospholipids, no change in the thermodenaturation temperature was observed, but a great increase in the enthalpy change of thermodenaturation resulted.     

Detection of a P-glycoprotein related pump in Chironomus larvae and its inhibition by verapamil and cyclosporin A

A membrane associated ATP-dependent efflux pump, similar in function to mammalian P-glycoprotein, was detected in anal papillae of Chironomus riparius larvae. Immunohistochemical analysis of larval tissues, using monoclonal antibodies against P-glycoprotein, was supplemented by functional in vivo and in vitro assays which confirmed the existence of a mechanism for transporting xenobiotic substances. The in vitro ATPase activity of homogenate fractions increased in the presence of typical P-glycoprotein substrates (vinblastine, actinomycin D or ivermectin). This increase was unaffected by inhibitors of other membrane ATPases (sodium azide, EGTA, ouabain), but sensitive to vanadate, cyclosporin A and verapamil which inhibit mammalian P-glycoprotein mediated ATP-consumption. Sublethal concentrations of specific P-glycoprotein-inhibitors such as verapamil or cyclosporin A synergistically enhanced the mortality of C. riparius towards ivermectin. Although cyclosporin A originates from entomopathogenic fungi, its mode of action in insects and its function during infection are not understood. Our results lend some credit to the hypothesis that this compound is possibly released to promote poisoning of the infected host by xenobiotics which are normally removed by a P-glycoprotein related pump. The putative role of insect P-glycoprotein homologues in the context of multiple resistance towards insecticides is discussed.     

Habitat preferences of cattail species and hybrids (Typha spp.) in eastern Canada

Interspecific hybridization is widespread in plants and is an important evolutionary process. Hybrids may be fitter than their parental species, at least under some environmental conditions, and this may lead to partitioning of taxa by habitat. In eastern Canada, two cattail species (Typha latifolia and Typha angustifolia) and their hybrid (Typha x glauca) are known to have become increasingly widespread in recent decades, although their habitat preferences and patterns of co-existence at the local scale are not well known. We quantified the occurrence of these three taxa in three different habitat types (high traffic, low traffic, and ‘natural’) at 40 different sites along a sampling route of approximately 2000 km in eastern Canada. There were no significant overall associations between habitat type and taxon, although intraspecific comparisons among sites showed that the hybrid was most likely to grow in high traffic (highly disturbed) sites. In addition, pairwise comparisons revealed significant independence of T. latifolia and T. angustifolia, although the hybrid was equally likely to co-exist with either of its parental species. The presence of the three taxa in several habitats, including highly disturbed roadside areas, is consistent with their increasingly invasive tendencies.     

Molecular genetic data reveal hybridization between Typha angustifolia and Typha latifolia across a broad spatial scale in eastern North America

A recent increase in the abundance of cattails (Typha spp.) in North American wetlands has been anecdotally linked with hybridization between Typha latifolia and Typha angustifolia. In this study, we used molecular genetic markers (microsatellites) to investigate whether the hybrid lineage (Typha × glauca) is restricted to The Great Lakes region, or exists across a much broader spatial scale. We also investigated the possibility of backcrossing and genetic introgression in natural populations. Parental species could be distinguished from one another based on the distribution of alleles at six microsatellite loci. Species identification based on genetic data corresponded well with species identifications based on leaf width, a key morphological trait that can distinguish the two parental species. We found that hybrids occur in Ontario, Quebec, New Brunswick, and Nova Scotia, but we did not detect hybrids in Maine. F₁s are more abundant than backcrossed or intercrossed hybrids, although we also found evidence of backcrossing, particularly in Ontario. This indicates that hybrids are fertile, and are therefore potential conduits of gene flow between the parental species. Further work is needed to determine whether T. × glauca is particularly successful in the Great Lakes region relative to other areas in which the two parental species co-exist, and to assess whether introgression may lead to increased invasiveness in the species complex.     

Stromata, sporangiomata and chlamydosori of Phytophthora ramorum on inoculated Mediterranean woody plants

Three types of multihyphal structures, stromata, sporangiomata and chlamydosori, are described for the plant pathogen Phytophthora ramorum. Their morphology, morphogenesis and position on the host organ were observed by dissecting, compound and scanning electron microscopy. Stromata were consistently formed one to two weeks after zoospore inoculation of detached leaves and fruits of an assortment of Mediterranean sclerophyll shrubs. Stroma initials appeared subcuticularly or subepidermally and developed as small hyphal aggregates by repeated branching, budding, swelling and interweaving, eventually forming a prosenchyma. They always emerged through the adaxial side of the leaf by rupture of the overlying host tissue. Occasionally sporangia and chlamydosori (packed clusters of chlamydospores) were formed on the stromata. Sporangiomata bore short sporangiophores and clusters of 20–100 sporangia and resembled sporodochia of the mitosporic fungi. The biological significance of these multihyphal structures is discussed. Some epidemiological aspects were also studied: several understorey species of the holm oak (Quercus ilex) woodland were susceptible to in vitro infection with three isolates of P. ramorum originally collected from different ornamental hosts. The risk of spread to this ecosystem is evaluated.     

Phylogeny of Caragana (Fabaceae) based on DNA sequence data from rbcL, trnS–trnG, and ITS

Phylogenetic relationships of 48 species of Caragana (Fabaceae: tribe Hedysareae) and one representative each of Astragalus, Calophaca, Halimodendron, and Hedysarum are estimated from DNA sequences of the rbcL gene, trnS–trnG intron and spacer, and ITS region. At least one representative of all five sections and 12 series within Caragana are included. Analyses yielded strongly supported clades corresponding to sections Caragana, Bracteolatae, and Frutescentes. The species of section Jubatae are distributed among three strongly supported clades, i.e., one with the species of section Bracteolatae, another with two species of section Spinosae, and a third as sister to section Frutescentes. All but the last of these six clades are corroborated by at least one unambiguously traced morphological character. The placement of the other four species of section Spinosae are not well supported and lack unambiguous morphological synapomorphies, and the samples of Calophaca and Halimodendron nest within Caragana with weak support.     

The role of programmed cell death in Plasmodium–mosquito interactions

Many host–parasite interactions are regulated in part by the programmed cell death of host cells or the parasite. Here we review evidence suggesting that programmed cell death occurs during the early stages of the development of the malaria parasite in its vector. Zygotes and ookinetes of Plasmodium berghei have been shown to die by programmed cell death (apoptosis) in the midgut lumen of the vector Anopheles stephensi, or whilst developing in vitro. Several morphological markers, indicative of apoptosis, are described and evidence for the involvement of a biochemical pathway involving cysteine proteases discussed in relationship to other protozoan parasites. Malaria infection induces apoptosis in the cells of two mosquito tissues, the midgut and the follicular epithelium. Observations on cell death in both these tissues are reviewed including the role of caspases as effector molecules and the rescue of resorbing follicles resulting from inhibition of caspases. Putative signal molecules that might induce parasite and vector apoptosis are suggested including nitric oxide, reactive nitrogen intermediates, oxygen radicals and endocrine balances. Finally, we suggest that programmed cell death may play a critical role in regulation of infection by the parasite and the host, and contribute to the success or not of parasite establishment and host survival.     

Host preference in Pseudacteon phorid flies: response of P. tricuspis and P. curvatus to black, red and hybrid imported Solenopsis fire ants in multiple choice bioassays

Host preferences in both sexes of Pseudacteon tricuspis Borgmeier (Jaguariuna biotype) and Pseudacteon curvatus Borgmeier (Formosa biotype) and their relative attraction to the imported fire ants (IFA), Solenopsis invicta Buren (red IFA), Solenopsis richteri Forel (black IFA) and S. invicta × S. richteri hybrids (hybrid IFA) were investigated in two separate experiments utilizing multiple choice flight bioassays. The results of both experiments clearly showed that both sexes of the Jaguariuna biotype of P. tricuspis could distinguish among the three IFA species and demonstrated greater preference for hybrid IFA and red IFA. This conclusion is supported by a variety of data collected on the number of fly visits, attack rate, and hovering duration (Experiment 1), and on the number of trapped flies (Experiment 2), which showed that black IFA is the least preferred of the three species. Similar results were recorded for the Formosan biotype of P. curvatus, although the data were not as strongly conclusive. Females of this biotype spent a significantly greater amount of time in hovering mode over red IFA and hybrid IFA compared to black IFA, but the other data were not significant. The red IFA is the natural host of both phorid fly biotypes and our results suggest that both biotypes may have evolved a specialized relationship with red IFA including an ability to discriminate it from related fire ants. These results are discussed in relation to the possible role of fire ant chemicals in mediating host preferences in phorid flies, contributions of male phorid flies to fire ant biocontrol, and the practical implications of the key findings.     

Parasite ligand–host receptor interactions during invasion of erythrocytes by Plasmodium merozoites

Malaria parasites must recognise and invade different cells during their life cycle. The efficiency with which Plasmodium falciparum invades erythrocytes of all ages is an important virulence factor, since the ability of the parasite to reach high levels of parasitemia is often associated with severe pathology and morbidity. The merozoite invasion of erythrocytes is a highly complex, multi-step process that is dependent on a cascade of specific molecular interactions. Although many proteins are known to play an important role in invasion, their functional characteristics remain unclear. Therefore, a complete understanding of the molecular interactions that are the basis of the invasion process is absolutely crucial, not only in improving our knowledge about the basic biology of the malarial parasite, but also for the development of intervention strategies to counter the disease. Here we review the current state of knowledge about the receptor–ligand interactions that mediate merozoite invasion of erythrocytes.     

Separate and interactive effects of competition and herbivory on the growth, expansion, and tuber formation of Hydrilla verticillata

This study examined the interaction and main-effect impacts of herbivory by the leaf-mining fly Hydrellia pakistanae and plant competition from Vallisneria americana on the growth, expansion and tuber formation of Hydrilla verticillata in a 2 × 2 factorial design experiment. The study was conducted in 14,000-L tanks, over two growing seasons. Each tank represented a single experimental unit and contained 32 1-L pots. At the beginning of the experiment half of these were planted with H. verticillata while the other half were either left empty or planted with V. americana (the competitor). H. pakistanae fly larvae (the herbivore) were added to tanks as appropriate. No significant interactions were identified between herbivory and competition on any parameter of H. verticillata growth analyzed (i.e., total tank biomass accumulation, total number of rooting stems, total tuber number, total tuber mass, and tuber size), indicating that the factors were operating independently and neither antagonism nor synergism was occurring. Both competition and herbivory impacted the growth of H. verticillata. H. verticillata plants grown in the presence of V. americana developed less total biomass, had fewer total basal stems, had fewer tubers and less tuber mass per tank, and produced significantly smaller tubers relative to control plants. Herbivory also suppressed H. verticillata biomass accumulation and tended to suppress the number and total mass of tubers produced in each tank. Both factors showed 30–40% reduction of total H. verticillata biomass, although the mechanism of impact was different. Competition suppressed expansion of H. verticillata into adjoining pots but had little impact on its growth in pots where it was originally planted. Herbivory resulted in a general suppression of growth of H. verticillata in all pots. Although herbivory significantly impacted H. verticillata biomass, it did not result in competitive release for V. americana under the current experimental conditions. We conclude that management activities that promote competition or herbivory will impact the growth and expansion of H. verticillata. Furthermore, since these factors operated independently, the combined use of both factors should be beneficial for suppression of H. verticillata dominance.     

The TonB protein of Yersinia enterocolitica and its interactions with TonB-box proteins

Summary The tonB gene is required for energy-dependent transport processes across the outer membrane of gram-negative bacteria. Using the antibiotics albomycin and ferrimycin, a tonB mutant of Yersinia enterocolitica was isolated. Comparison of the tonB mutant with the parent strain revealed that in Y. enterocolitica the uptake of ferrioxamine, ferrichrome, pesticin and heme is TonB-dependent. The tonB gene from Y. enterocolitica was sequenced and found to be similar to those of other Enterobacteria. The Y. enterocolitica tonB gene complemented a Y. enterocolitica tonB mutant. In contrast, some Tong functions of an Escherichia coli tonB mutant were not restored by the tonB gene of Y. enterocolitica. The observed differences in the ability to complement E. coli Tong functions correlated with the degree to which the Tong boxes of the receptors and colicins differed from the TonB box consensus sequence. Furthermore, the N-terminal membrane anchor of the TonB proteins and the TolA protein are likely to form an -helix with an identical sequence motif (SHLS) located at one face of the a-helix, suggesting this region to be involved in the functional cross-talk between the TonB-ExbBD-and TolABQR-dependent transport systems across the outer membrane.