Relationships between the stereochemistry and biological activity of fungal phytotoxins

Toxins produced by phytopathogenic fungi assume great importance because of their involvement in several plant diseases. Although such pathogens are known to have seriously damaged crops, forest, and environmental resources, they represent a very important tool to develop new environmentally friendly herbicides and fungicides. This review deals with the relationships between the biological activity of some phytotoxins produced by pathogenic fungi for major forest plants and for damaging weeds and their stereochemistry. In particular, the methods used to determine their relative and/or absolute configuration will be illustrated. These include the application of Mosher's and Murata's methods, X-ray diffractometric analysis, circular dichroism, and the use of computational methods to determine the theoretical optical rotatory power as well as the CD spectrum. The importance of determining the absolute configuration to achieve the total synthesis of some phytotoxins, interesting for their potential practical application, is also discussed.     

A review of fungal phytotoxins: from basic studies to practical use

Recent materials are summarized, pertaining to classification of fungal phytotoxins, methods of their isolation, and assays for biological activity. Producers of phytotoxic substances have been characterized, and the chemical nature of phytotoxins has been subjected to analysis. The review gives consideration to the mechanisms of action of phytotoxins on susceptible plants and the mechanisms of plant resistance to such agents. Other matters discussed include prospects of utilizing basic knowledge of the nature and mechanisms of action of phytotoxins for (1) developing means of plant protection against diseases and weeds and (2) identifying or classifying fungi (chemosystematics).     

Mechanisms of phosphate solubilization by fungal isolates when exposed to different P sources

The use of phosphate-solubilizing fungi is a promising biotechnological strategy in the management of phosphorus (P) fertilization, as it enables the utilization of rock phosphates (RP) or the recovery of P fixed in soil particles. The objective of our study was to evaluate fungal isolates for mechanisms of solubilization of P-bearing compounds, such as AlPO₄, FePO₄, Ca₃(PO₄)₂, Araxá RP, and Catalão RP. Four fungal isolates obtained from Brazilian soils were characterized in liquid media: Aspergillus niger FS1, Penicillium canescens FS23, Eupenicillium ludwigii FS27, and Penicillium islandicum FS30. A. niger FS1 was the only isolate able to solubilize all of the P sources, solubilizing 71, 36, 100, and 14 % of the P from AlPO₄, FePO₄, Ca₃(PO₄)₂, and RPs, respectively. Medium acidification was an effective solubilization mechanism, particularly for Ca₃(PO₄)₂. The other P sources were mainly solubilized through organic acids produced by the fungi. Oxalic acid, produced exclusively by A. niger FS1, and citric acid were decisive factors in the solubilization of AlPO₄ and FePO₄. Penicillium isolates produced more gluconic acid than A. niger FS1 in all treatments. However, this higher production did not result in higher solubilization for any of the P sources, showing that gluconic acid contributes little to the solubilization of the P sources evaluated. The higher capacity of medium acidification and the production of organic acids with stronger metal-complexation activity are characteristics that confer to A. niger FS1 a wider action on insoluble P sources. Consequently, this isolate qualifies as a promising candidate for application in the management of P fertilization.     

Secondary fungal metabolites (mycotoxins) in lichens of different taxonomic groups

Secondary fungal metabolites (mycotoxins) in 22 lichen species of the families Parmeliaceae, Nephromataceae, Umbilicariaceae, Ramalinaceae, Cladoniaceae, Peltigeraceae, and Teloschistaceae were determined by enzyme-linked immunosorbent assay. The following mycotoxins were found in these lichens in a broad concentration range with a frequency of 70–100%: sterigmatocystin (7–2090 ng/g), alternariol (20–6460 ng/g), and emodin (45–94500 ng/g). Mycophenolic acid frequently occurred in 19 lichen species; citrinin, in 17 species; diacetoxyscirpenol, in 11 species; cyclopiazonic acid, in 10 species; and zearalenone, in 9 species. PR toxin was regularly detected in three lichen species; deoxynivalenol, fumonisins, and ochratoxin A, in two species; and T-2 toxin and ergot alkaloids, in one species. Aflatoxin B₁ was detected in only six species with a frequency of 2–42%, whereas roridin A was present in 10% of Hypogymnia physodes samples.     

Soil fungal pathogens and the relationship between plant diversity and productivity

One robust result from many small-scale experiments has been that plant community productivity often increases with increasing plant diversity. Most frequently, resource-based or competitive interactions are thought to drive this positive diversity-productivity relationship. Here, we ask whether suppression of plant productivity by soil fungal pathogens might also drive a positive diversity-productivity relationship. We created plant assemblages that varied in diversity and crossed this with a ± soil fungicide treatment. In control (non-fungicide treated) assemblages there was a strong positive relationship between plant diversity and above-ground plant biomass. However, in fungicide-treated assemblages this relationship disappeared. This occurred because fungicide increased plant production by an average of 141% at the lower ends of diversity but boosted production by an average of only 33% at the higher ends of diversity, essentially flattening the diversity-productivity curve. These results suggest that soil pathogens might be a heretofore unappreciated driver of diversity-productivity relationships.     

Species confirmation of fungal isolates by molecular analysis

Traditional taxonomy of hyphomycetes has been based on conidial morphology and development. In order to confirm species level for the detection and identification of the entomopathogenic fungus, we analysed the species-specific fingerprints to investigate molecular characteristics within isolates of six species and to resolve morphologically atypical isolates. The extent of fingerprint profile observed by RAPD was sufficient to confirm the species level of all the isolates. The genetic similarity among morphologically identified isolates of each species was considerably higher, allowing us to conclude that all the isolates are of same species. These results establish a molecular framework for further taxonomic, phylogenetic and comparative biological investigations.     

Evolutionary relationship between different subgroups of restriction endonucleases

The type II restriction endonuclease SsoII shows sequence similarity with 10 other restriction endonucleases, among them the type IIE restriction endonuclease EcoRII, which requires binding to an effector site for efficient DNA cleavage, and the type IIF restriction endonuclease NgoMIV, which is active as a homotetramer and cleaves DNA with two recognition sites in a concerted reaction. We show here that SsoII is an orthodox type II enzyme, which is active as a homodimer and does not require activation by binding to an effector site. Nevertheless, it shares with EcoRII and NgoMIV a very similar DNA-binding site and catalytic center as shown here by a mutational analysis, indicative of an evolutionary relationship between these three enzymes. We suggest that a similar relationship exists between other orthodox type II, type IIE, and type IIF restriction endonucleases. This may explain why similarities may be more pronounced between members of different subtypes of restriction enzymes than among the members of a given subtype.     

Agropyrenol and agropyrenal,phytotoxins from Ascochyta agropyrina var. nana,a fungal pathogen of Elitrigia repens

A strain of Ascochyta agropyrina var. nana, a fungal pathogen of the perennial weed Elytrigia repens, produced several toxins in a liquid medium, and its primary toxin, named agropyrenol, was characterized as a substituted salicylaldehyde on the basis of its chemical and spectroscopic properties. Its absolute stereochemistry was determined by Mosher’s method. Two other minor metabolites were isolated from the same culture and named agropyrenal and agropyrenone, respectively. They were characterized as a trisubstituted naphthalene carbaldehyde and a pentasubstituted 3H-benzofuranone, respectively, using the same techniques. When assayed on leaves of several weed plants, i.e., Mercurialis annua, Chenopodium album and Setaria viridis, agropyrenol proved to be phytotoxic, causing the appearance of necrotic lesions, agropyrenal was less active, while agropyrenone was inactive. None of the compounds showed antibiotic, fungicidal or zootoxic activity.     

Establishment and characterization of Rubus tissue culture systems for in vitro bioassays against phytotoxins from Rubus fungal pathogens

The Rubus species R. parviflorus, R. spectabilis and R. strigosus interfere with conifer seedling establishment on forest regeneration sites in Canada and the United States. As a first step towards microbial metabolite-based control, callus and cell suspension cultures of the Rubus species were developed as a bioassay system to detect phytotoxic compounds that may have relevance in a vegetation control context. Rapidly growing friable callus and suspension cultures were obtained from leaf disks of the three weedy Rubus species using similar culture media conditions (modified Murashige and Skoog) but required different plant growth regulators (R. parviflorus, 4.5 M 2,4-D; R. spectabilis, 26.9 M NAA/0.5 M zeatin; and R. strigosus, 12.4 M picloram). Cell growth and health attributes including callus circumference, degree of browning and suspension culture cell viability as measured by the TTC vital stain assay were developed and were rapid and convenient to use. We have established Rubus tissue culture systems that will make it possible for large scale screening of phytotoxic metabolites.     

The developing relationship between the study of fungal communities and community ecology theory

Plant and animal systems had a head start of several decades in community ecology and have largely created the theoretical framework for the field. I argue that the lag in fungal community ecology was largely due to the microscopic nature of fungi that makes observing species and counting their numbers difficult. Thus the basic patterns of fungal occurrence were, until recently, largely invisible. With the development of molecular methods, especially high-throughput sequencing, fungal communities can now be “seen”, and the field has grown dramatically in response. The results of these studies have given us unprecedented views of fungal communities in novel habitats and at broader scales. From these advances we now have the ability to see pattern, compare it to existing theory, and derive new hypotheses about the way communities are assembled, structured, and behave. But can fungal systems contribute to the development of theory in the broader realm of community ecology? The answer to this question is yes! In fact fungal systems already have contributed, because in addition to many important natural fungal communities, fungi also offer exceptional experimental communities that allow one to manipulate, control, isolate and test key mechanisms. I discuss five well-developed systems and some of the contributions they have made to community ecology, and I briefly mention one additional system that is amenable to development.     

基于表型性状的芍药不同品种群亲缘关系分析

芍药品种变异丰富,表型性状的研究对各品种进行科学分类及亲缘关系的研究具有重要意义。本研究以芍药DUS测试指南(2012版)为依据,以不同品种群的47个芍药品种为研究对象,选取了株高、分枝能力、茎秆颜色等33个表型性状(二元性状9个,数量多态性状3个,定性多态性状21个)进行了R型聚类分析、主成分分析和Q型聚类分析。结果表明:基于33个表型性状的聚类结果可以较好地区分芍药不同品种群的品种,其中国内品种与大多数国外品种亲缘关系较远;杂种芍药品种群的品种由于多亲本参与,起源复杂,聚类结果比较分散;伊藤品种群与杂种芍药品种群存在较近亲缘关系。本研究与前人利用形态和分子标记进行品种分类的结果基本一致,能够较准确反映品种间、品种群间的亲缘关系。     

Screening of some wild fungal isolates for cellulolytic activities

Six wild fungal strains, Trichoderma viride, T. harzianum, Gliocladium virens, Aspergillus terreus, A. niger and Tiarosporella phaseolina , isolated from decomposed jute stacks and diseased jute stem, were tested for their cellulolytic and hemicellulolytic activities and compared with T. reesei MCG 77. Filter paper cellulase production by all these wild strains were lower than those produced by T. reesei while some strains ( T. viride, T. harzianum and G. virens ) possessed carboxymethyl cellulase, β-glucosidase, xylanase and β-xylosidase activities comparable to T. reesei. A. terreus and A. niger produced 3·2 and 1·2 times respectively, greater β-glucosidase activity compared to T. reesei when grown on microcrystalline cellulose.     

Diversity of fungal isolates from three Hawaiian marine sponges

Sponges harbor diverse prokaryotic and eukaryotic microbes. However, the nature of sponge-fungal association and diversity of sponge-derived fungi have barely been addressed. In this study, the cultivation-dependent approach was applied to study fungal diversity in the Hawaiian sponges Gelliodes fibrosa, Haliclona caerulea, and Mycale armata. The cultivated fungal isolates were representatives of 8 taxonomic orders, belonging to at least 25 genera of Ascomycota and 1 of Basidiomycota. A portion of these isolates (n=15, 17%) were closely affiliated with fungal isolates isolated from other marine habitats; the rest of the isolates had affiliation with terrestrial fungal strains. Cultivated fungal isolates were classified into 3 groups: 'sponge-generalists'-found in all sponge species, 'sponge-associates'-found in more than one sponge species, and 'sponge-specialists'-found only in one sponge species. Individuals of G. fibrosa collected at two different locations shared the same group of 'sponge-specialists'. Also, representatives of 15 genera were identified for the first time in marine sponges. Large-scale phylogenetic analysis of sponge-derived fungi may provide critical information to distinguish between 'resident fungi' and 'transient fungi' in sponges as it has been done in other marine microbial groups. This is the first report of the host specificity analysis of culturable fungal communities in marine sponges.     

Canonical correlation between groups of acarine,fungal and environmental variables in bulk grain ecosystems

Interrelations among acarine, fungal, and environmental components of bulk grain ecosystems were determined by canonical correlation analyses. Twenty-seven variables were measured monthly in samples collected from 2 identical grain bulks in a granary in Winnipeg during the years 1959–67. The relationships between 9 kinds of arthropods and 6 environ mental variables, and between the same arthropods and 12 kinds of actinomycetes and fungi were examined. The maximum canonical correlation between arthropods and environmental factors was 0.35, and between arthropods and microorganisms was 0.28; both are highly significant (p<0.001). In the first analysis correlations of the variables with the canonical variates revealed that correlations of the variables with the canonical variates revealed that sampling location, depth, and temperature are the primary environmental antecedents involved, and the criterion is primarily composed of mites Tarsonemus spp.,Tydeus interruptus and the psocid, Lepinotus reticulatus. In the second analysis the fungi Nigrospora sphaerica, Aspergillus spp., and Cochliobolus sativus are involved with the mites Cheyletus eruditus and Acarus siro. Generally, the results of these analyses complement the findings of factor and regression analyses of the same data reported earlier.     

Numerical study to establish relationship between coagulation volume and target tip temperature during temperature-controlled radiofrequency ablation

The present study aims at proposing a relationship between the coagulation volume and the target tip temperature in different tissues (viz., liver, lung, kidney, and breast) during temperature-controlled radiofrequency ablation (RFA). A 20-min RFA has been modelled using commercially available monopolar multi-tine electrode subjected to different target tip temperatures that varied from 70°C to 100°C with an increment of 10°C. A closed-loop feedback proportional-integral-derivative (PID) controller has been employed within the finite element model to perform temperature-controlled RFA. The coagulation necrosis has been attained by solving the coupled electric field distribution, the Pennes bioheat and the first-order Arrhenius rate equations within the three-dimensional finite element model of different tissues. The computational study considers temperature-dependent electrical and thermal conductivities along with the non-linear piecewise model of blood perfusion. The comparison between coagulation volume obtained from the numerical and in vitro experimental studies has been done to evaluate the aptness of the numerical models. In the present study, a total of 20 numerical simulations have been performed along with 12 experiments on tissue-mimicking phantom gel using RFA device. The study revealed a strong dependence of the coagulation volume on the pre-set target tip temperature and ablation time during RFA application. Further, the effect of target tip temperature on the applied input voltage has been studied in different tissues. Based on the results attained from the numerical study, statistical correlations between the coagulation volume and treatment time have been developed at different target tip temperatures for each tissue.     

Immunological relationship between different types of bovine intermediate filaments

In order to examine the relationship between the intermediate filaments from Purkinje fibres of the cow heart conduction system and five proposed subclasses of mammalian intermediate filaments, the gel electrophoresis-derived enzyme-linked immunosorbent assay (GEDELISA) has been used to examine the specificity and crossreactivity of our antibodies against the Purkinje fibre intermediate filament protein, skeletin. Bovine tissues known to contain intermediate filaments of the five main subclasses were examined with antiskeletin and with preimmune serum and the specific antiserum absorbed with pure skeletin as controls. The antibodies raised against Purkinje fibre skeletin reacted with all three polypeptides of the "neurofilament triplet", with glial fibrillary acidic protein (GFAP), with smooth muscle desmin and also slightly with some prekeratin subunits and with endothelial vimentin. From studies with monoclonal antibodies and amino acid sequencing, certain regions of all intermediate filaments are suggested to be structurally related. Here we show that Purkinje fibre skeletin seems to share antigenic determinants with the proposed five main classes of intermediate filaments. Our antibody is the first carefully controlled experimentally induced antibody having such properties. This might be due to the special attributes of the intermediate filament system in Purkinje fibres, which themselves have unique properties.     

The relationship between different forms of human alpha-mannosidase.

The tissue distribution and some properties of human alpha-mannosidase (alpha-D-mannoside mannohydrolase EC 3.2.1.24) have been studied. The acidic forms of the enzyme were fairly stable, whereas the neutral forms easily lost enzymic activity. The acidic forms were sensitive to neuraminidase but the neutral forms were unaffected. The experiments indicate that the acidic components are closely related to each other, differing only in sialic acid content and possibly conformation. The neutral forms of the enzyme are probably quite different from the acidic forms both in structure and cellular function.