Anatomical relations among endophytic holoparasitic angiosperms, autotrophic host plants and mycorrhizal fungi: A novel tripartite interaction

Mycorrhizae are widespread mutualistic symbioses crucial for the functioning of terrestrial ecosystems. Not all plants associate with mycorrhizae; most parasitic plants have been suggested to be nonmycorrhizal because they have developed alternative strategies to obtain nutrients. In endophytic parasitic plants, whose vegetative bodies grow completely inside their mycorrhizal host roots, the opportunity for establishing a tripartite association seems evident, but information on these systems is lacking. In studying natural associations among the endophytic holoparasite Cytinus hypocistis, their Cistaceae host species, and associated mycorrhizal fungi, we found that mycorrhizae were associated with the hosts and the parasites, reaching high frequencies of colonization. In parasitic and host root tissues, mycorrhizal fungi spread in the parenchymatic cells by intracellular growth and formed hyphal coils and vesicles, while the cambium and the vascular tissues were never colonized. This report is the first on a tripartite association of an endophytic parasitic plant, its host, and mycorrhizae in natural conditions, representing a novel trophic interaction not previously reported within the angiosperms. Additional studies on the interactions occurring among these three players are needed because they may be crucial to our understanding of how this mutualistic-antagonistic system is functioning and evolving.     

Shifting patterns of nitrogen excretion and amino acid catabolism capacity during the life cycle of the sea lamprey (Petromyzon marinus)

The jawless fish, the sea lamprey (Petromyzon marinus), spends part of its life as a burrow-dwelling, suspension-feeding larva (ammocoete) before undergoing a metamorphosis into a free swimming, parasitic juvenile that feeds on the blood of fishes. We predicted that animals in this juvenile, parasitic stage have a great capacity for catabolizing amino acids when large quantities of protein-rich blood are ingested. The sixfold to 20-fold greater ammonia excretion rates (J(Amm)) in postmetamorphic (nonfeeding) and parasitic lampreys compared with ammocoetes suggested that basal rates of amino acid catabolism increased following metamorphosis. This was likely due to a greater basal amino acid catabolizing capacity in which there was a sixfold higher hepatic glutamate dehydrogenase (GDH) activity in parasitic lampreys compared with ammocoetes. Immunoblotting also revealed that GDH quantity was 10-fold and threefold greater in parasitic lampreys than in ammocoetes and upstream migrant lampreys, respectively. Higher hepatic alanine and aspartate aminotransferase activities in the parasitic lampreys also suggested an enhanced amino acid catabolizing capacity in this life stage. In contrast to parasitic lampreys, the twofold larger free amino acid pool in the muscle of upstream migrant lampreys confirmed that this period of natural starvation is accompanied by a prominent proteolysis. Carbamoyl phosphate synthetase III was detected at low levels in the liver of parasitic and upstream migrant lampreys, but there was no evidence of extrahepatic (muscle, intestine) urea production via the ornithine urea cycle. However, detection of arginase activity and high concentrations of arginine in the liver at all life stages examined infers that arginine hydrolysis is an important source of urea. We conclude that metamorphosis is accompanied by a metabolic reorganization that increases the capacity of parasitic sea lampreys to catabolize intermittently large amino acid loads arising from the ingestion of protein rich blood from their prey/hosts. The subsequent generation of energy-rich carbon skeletons can then be oxidized or retained for glycogen and fatty acid synthesis, which are essential fuels for the upstream migratory and spawning phases of the sea lamprey's life cycle.     

Cloning and characterization of two neuropeptide genes from cereal cyst nematode, Heterodera avanae from India

The cereal cyst nematode, Heterodera avenae (Wollenweber, 1924) is one of the most important plant parasitic nematodes of cereals. It is an obligate sedentary endo parasite causing considerable crop losses in wheat, barley and oats worldwide. FMRFamide-like peptides (FLPs) play critical role as neurotransmitters or neuromodulators in the nervous system and proposed as one of the important targets for the plant parasitic nematode management. Therefore, for the first time we have cloned and characterized two neuropeptide genes (flp-12 and flp-16) from the cDNA library of feeding female of H. avenae. Sequence analysis of FLPs revealed that both the neuropeptides are closely related with the parasitic as well as free-living nematodes. The flp-12 contains putative 22 residue long signal peptide at N-terminal suggesting its association with extra-cellular functions, while flp-16 does not contain signal peptide. Besides this, we have found highly conserved motif KFEFIRF in flp-12 and RFGK motif in flp-16. These two flp genes could be interesting and potential targets for functional validation to explore their utility for designing management strategies.     

Nestling competition,rather than supernormal stimulus,explains the success of parasitic brown-headed cowbird chicks in yellow warbler nests

Interspecific parasitic chicks are usually fed more than the smaller host young with whom they share the nest. This could be due to parasitic chicks having evolved exaggerated features that are preferred by the adults to the features present in their own young (the supernormal stimulus hypothesis). Alternatively, the success of parasitic chicks could be due to them being better competitors. We tested these hypotheses by studying the interaction between brown-headed cowbird chicks, Molothrus ater, and a common small host, the yellow warbler, Dendroica petechia. Parasitic chicks begged more intensively than the host''s young and received most of the feeds. The relative height reached by the begging chicks of both species was the most important variable in determining their feeding success. Being larger and begging intensively, brown-headed cowbirds were better able to reach higher than the host''s young, but at equal heights parasitic chicks were no better than the host''s young at gaining feeds. It is suggested that the success of the brown-headed cowbirds when parasitizing yellow warblers is due to them physically out-competing the smaller young of their hosts, and not to them evoking a stronger response from the hosts by being a supernormal stimulus.     

Cuban parasitology in review: a revolutionary triumph

Although the population of Hispaniola, Cuba's most similar neighbour in the Caribbean, continues to be threatened by parasitic diseases (including malaria), many tropical parasitic infections in Cuba have been eliminated or controlled. However, some parasitic infections remain important in the Cuban population, and the occurrence of vectors and the high possibility of introduction of parasites mean that Cuban diagnosticians must remain alert. Some key aspects of human parasitology in Cuba are reviewed here, including historical information, comparative data from Hispaniola and Jamaica, and how Cuba strives to maintain and improve its control against parasitic infections. Data from recent key novel parasitology research conducted in Cuba are also described.     

Thermoinhibition uncovers a role for strigolactones in Arabidopsis seed germination

Strigolactones are host factors that stimulate seed germination of parasitic plant species such as Striga and Orobanche. This hormone is also important in shoot branching architecture and photomorphogenic development. Strigolactone biosynthetic and signaling mutants in model systems, unlike parasitic plants, only show seed germination phenotypes under limited growth condition. To understand the roles of strigolactones in seed germination, it is necessary to develop a tractable experimental system using model plants such as Arabidopsis. Here, we report that thermoinhibition, which involves exposing seeds to high temperatures, uncovers a clear role for strigolactones in promoting Arabidopsis seed germination. Both strigolactone biosynthetic and signaling mutants showed increased sensitivity to seed thermoinhibition. The synthetic strigolactone GR24 rescued germination of thermoinbibited biosynthetic mutant seeds but not a signaling mutant. Hormone analysis revealed that strigolactones alleviate thermoinhibition by modulating levels of the two plant hormones, GA and ABA. We also showed that GR24 was able to counteract secondary dormancy in Arabidopsis ecotype Columbia (Col) and Cape Verde island (Cvi). Systematic hormone analysis of germinating Striga helmonthica seeds suggested a common mechanism between the parasitic and non-parasitic seeds with respect to how hormones regulate germination. Thus, our simple assay system using Arabidopsis thermoinhibition allows comparisons to determine similarities and differences between parasitic plants and model experimental systems for the use of strigolactones.     

生物因子对寄生蜂滞育的影响

在影响寄生蜂滞育的生物因子中,寄主及亲代是主要影响因子。寄主可以从种类、类型、生理状态及丰富度等方面影响寄生蜂的滞育:寄生不同种类的寄主,寄生蜂的滞育反应、滞育进度、滞育比例以及光周期反应表现等均有不同;寄主类型的影响在蚜茧蜂类群中表现最为突出,不同寄主类型能对蚜茧蜂的滞育诱导产生不同影响;此外,寄主生理状态和寄主丰富度也是影响寄生蜂滞育的重要因子。亲代对寄生蜂滞育的影响则通过其所经历的环境条件以及自身因素等方面来表现:亲代经历的光周期和温度等能显著影响子代的滞育,甚至起完全决定作用;在亲代自身因素的影响中,亲代虫龄差异是主要因素。本文同时对寄生蜂滞育的研究及应用前景也一并作了展望。     

The epidemic process as a system. The social regulators of the epidemic process

The article deals with the mechanisms of spontaneous (urbanization, the international migration of population, the anthropogenic transformation of nature) and goal-oriented regulatory action on the epidemic process. Social factors have been shown to transform into ecological ones with the subsequent transformation of information in the parasitic system and their reflection in the social subsystem as the indices of the risk of infection and its socio-economical importance. Using the processes of urbanization as an example, the present work demonstrates that the mechanism of transmission acts as a filter whose specific features are determined by a range of social factors playing the most important role in the regulation of the epidemic process on the socio-ecosystemic level of its organization.     

Implication of chromosomal analysis for the taxonomy of parasitic wasps (hymenoptera)

A review of principles for application of the morphology of the karyotype in the taxonomy of parasitic wasps is given. Specific character of the use of chromosomal characteristics at different taxonomic levels is determined. In the taxonomy of hymenopterans, the data on the morphology of the karyotype are the most important at the species level. By the taxonomic level and the degree of morphological isolation, closely related species of parasitic wasps, differing in the structure of chromosomal sets, can be subdivided into the following groups: well-distinguishable species; species with indistinct differences in the appearance (proper sibling species); morphologically identical populations; intrapopulation forms; specimens with spontaneous chromosomal mutations. It is suggested that chromosomal studies in the taxonomy of hymenopterans should be used as a method of express analysis of outdoor populations and laboratory strains of these insects.     

Proposal for changes in cystoscopic follow up of patients with bladder cancer and adjuvant intravesical chemotherapy.

A famous surgeon observed that the most important instrument for the management of superficial bladder cancer was a typewriter because it facilitated the organisation of the regular follow up examinations that are so important in controlling this disease. Cystoscopic follow up must be lifelong, and the cost, in the broadest sense, to both patient and health service is considerable. A recent study has suggested that the conventional frequency of bladder examinations may not be necessary and that most patients could be spared many cystoscopies. Instillation of cytotoxic drugs in the bladder has been shown to reduce the recurrence of tumours destroyed endoscopically and the development of new tumours elsewhere in the bladder. Because intravesical instillations are inconvenient, expensive, and may be toxic they have been reserved for patients thought to be at greatest risk of recurrence. However, two clinical trials have shown that a single cytotoxic instillation may be beneficial for low risk patients. If this is verified in everyday practice, the routine use of intravesical chemotherapy for all patients at the time of initial treatment could reduce the need for cystoscopies even further. Such changes should improve the quality of life of the 7000 new patients with superficial bladder cancer each year in England and Wales and allow savings to be made in the NHS.     

A syndromic approach to common parasitic diseases

Standard textbooks discuss parasitic disease according to specific organisms. In contrast, patients with parasitic infections present to physicians with a variety of clinical manifestations that may involve any of several organ systems and that often mimic nonparasitic diseases. A syndromic approach to the clinical situation may help the physician in considering the most important parasitic agents. Many parasitic infections can be acquired in temperate climates. While often considered tropical or exotic, other parasitic diseases are now seen more frequently in developed countries because of immigration and increased world travel. In this review the clinical syndromes associated with common parasitic diseases in North America are discussed, with an emphasis on risk factors and diagnosis of specific infections.     

Selfish DNA and breeding system in flowering plants

In many species, some individuals carry one or more B chromosomes: extra, or supernumerary chromosomes not part of the normal complement. In most well-studied cases, Bs lower the fitness of their carrier and persist in populations only because of accumulation mechanisms analogous to meiotic drive. It has been suggested that such genomic parasites are expected to persist only in outcrossed sexual species, in which uninfected lines of descent can be continuously reinfected; in inbred or asexual species, all selection is between lines of descent, and the genomic parasites are either lost or must evolve into commensals or mutualists. Here we present a simple population genetic model of the effect of outcrossing rate on the frequency of B chromosomes, and find that outcrossing facilitates the spread of parasitic Bs, but inhibits the spread of mutualists. Data compiled from the literature on breeding system and B chromosomes of British plants indicate that Bs are much more likely to be reported from obligately outcrossed species than inbred species. These results support the ideas that most B chromosomes are parasitic, and that breeding systems play a central role in the biology of selfish genes.     

寄生植物对寄主植物的化学识别

植物间寄生关系的研究近年来受到了广泛的重视。大量的研究表明,寄主释放的次生物质对植物间寄生关系的建立和维持起了重要的调节作用。寄主植物的次生物质对寄生植物的化学防御和昆虫授粉等生态功能起重要的作用,寄主植物次生物质对寄生植物生理与生态的调节作用是受寄生植物基因调节的。更为重要的是寄主植物释放的次生物质成为寄生植物的种子萌发和吸器发生的异源识别物质。能够刺激寄生植物种子萌发的次生物质主要是倍半萜和氢醌类物质,而诱导吸器发生的物质则是酚酸、醌和黄酮类化合物,诱导吸器发生的核心结构是对苯醌。这些异源识别物质大多是寄主植物释放的化感抑制物质,显示寄生植物在化学防御方面要比寄主植物高级。异源识别化合物的活性与其氧化潜力显著相关。由于寄生植物中存在一抑制异源识别物质诱导吸器发生的调节过程,因此吸器的产生与寄生植物根部接触异源识别物质的浓度与时间呈正相关关系,这一调节过程对寄生植物准确识别寄主并寄生其上是十分重要的。对寄生植物和寄主植物间的化学识别关系的揭示有助于人们防治有害寄生植物和开发利用有价值的寄生植物资源。     

肝囊型包虫病非手术治疗方法的研究进展

肝囊型包虫病(简称肝包虫病)是一种由细粒棘球蚴感染肝脏引起的人兽共患寄生虫病,严重危害人类以及家畜的健康。近年来,由于该病术后复发率较高且易出现并发症,非手术治疗方法如介入技术、放射治疗以及药物治疗均得到了不断的发展。介入技术对于肝包虫病的治疗是一种比较新颖的方法,其临床应用时间较短,主要包括经皮穿刺治疗、射频消融、门静脉栓塞,以经皮穿刺治疗最为常见。放射治疗肝包虫病尚处于研究阶段,效果尚不完全明确。苯并咪唑类药物及其新剂型、非苯并咪唑类药物如地塞米松等及中草药治疗肝包虫病也均具有各自的优缺点。本文主要对上述非手术治疗方法及优缺点进行了综述。     

Parasitic wasp assemblages associated with native and weedy plant species in an agricultural landscape

Abstract  The establishment and maintenance of suitable habitat on-farm or in the surrounding landscape can enhance the survival of beneficial parasitic Hymenoptera, thus improving the control of pest species. Both endemic and weedy non-crop plant species across a highly modified agricultural landscape supported species-rich and abundant parasitic wasp assemblages with diverse biology and host associations. It was also shown that isolated, recently planted, single-species stands of plants can rapidly accumulate diverse assemblages of parasitoids. Chalcidoidea was the most species-rich and abundant group, egg and larval parasitoids were the most speciose and abundant guilds, and parasitoids of herbivorous insects feeding on and inside plant tissue were the most species-rich and abundant functional groups. The hymenopteran assemblages associated with the majority of plant species were dominated by three parasitoid species: a Trichogrammatidae, a Scelionidae ( Telenomus sp.) and a Eulophidae ( Ceranisus sp.), all genera that contain many important biocontrol agents of pest Lepidoptera, Hemiptera and Thysanoptera. Results show that both native and weedy plant species may potentially provide an important reservoir of mobile parasitic wasps of benefit to crop protection.     

Analysis of classical neurotransmitter markers in tapeworms: Evidence for extensive loss of neurotransmitter pathways

Parasitic flatworms have complex neuromuscular systems that serve important functions in their life cycles. However, our understanding of neurotransmission in parasitic flatworms is limited. Pioneering studies have suggested the presence of several classical neurotransmitter systems, but their molecular components have not been characterized in most cases. Because these components are conserved in bilaterian animals, we searched the genomes of parasitic flatworms for orthologs of genes required for neurotransmitter synthesis, vesicular transport, reuptake, and reception. Our results indicate that tapeworms have lost the genes that are specifically required in other animals for synaptic signaling using the classical neurotransmitters dopamine, tyramine, octopamine, histamine and gamma-aminobutyric acid (GABA). These results imply that these signaling pathways are either absent in these parasites, or that they require completely different molecular components in comparison with other animals. The orthologs of genes related to histaminergic and GABA signaling are also missing in trematodes (although Schistosoma-specific histaminergic receptors have been previously described). In contrast, conserved genes required for glutamatergic, serotonergic and cholinergic signaling could be found in all analyzed flatworms. We analyzed the expression of selected markers of each pathway in the tapeworm Hymenolepis microstoma by whole-mount in situ hybridization. Each marker was specifically expressed in the nervous system, although with different patterns. In addition, we analyzed the expression of proprotein convertase 2 as a marker of peptidergic cells. This gene showed the widest expression in the nervous system, but was also expressed in other tissues, suggesting additional roles of peptidergic signaling in tapeworm development and reproduction.     

Fish-borne parasitic zoonoses: status and issues

The fish-borne parasitic zoonoses have been limited for the most part to populations living in low- and middle-income countries, but the geographical limits and populations at risk are expanding because of growing international markets, improved transportation systems, and demographic changes such as population movements. While many in developed countries will recognize meat-borne zoonoses such as trichinellosis and cysticercosis, far fewer are acquainted with the fish-borne parasitic zoonoses which are mostly helminthic diseases caused by trematodes, cestodes and nematodes. Yet these zoonoses are responsible for large numbers of human infections around the world. The list of potential fish-borne parasitic zoonoses is quite large. However, in this review, emphasis has been placed on liver fluke diseases such as clonorchiasis, opisthorchiasis and metorchiasis, as well as on intestinal trematodiasis (the heterophyids and echinostomes), anisakiasis (due to Anisakis simplex larvae), and diphyllobothriasis. The life cycles, distributions, epidemiology, clinical aspects, and, importantly, the research needed for improved risk assessments, clinical management and prevention and control of these important parasitic diseases are reviewed.