Growth and biomass of mycorrhizal mycelia in coniferous forests along short natural nutrient gradients

Hybridization may lead to unique phytochemical expression in plant individuals. Hybrids may express novel combinations or extreme concentrations of secondary metabolites or, in some cases, produce metabolites novel to both parental species. Here we test whether there is evidence for extreme metabolite expression or novelty in F1 hybrids between Senecio aquaticus and Senecio jacobaea. Hybridization is thought to occur frequently within Senecio, and hybridization might facilitate secondary metabolite diversification within this genus. Parental species express different quantities of several classes of compounds known to be involved in antiherbivore defence, including pyrrolizidine alkaloids, chlorogenic acid, flavonoids and benzoquinoids. Hybrids demonstrate differential expression of some metabolites, producing lower concentrations of amino acids, and perhaps flavonoids, than either parental species. Despite evidence for quantitative hybrid novelty in this system, NMR profiling did not detect any novel compounds among the plant groups studied. Metabolomic profiling is a useful technique for identifying qualitative changes in major metabolites according to plant species and/or genotype, but is less useful for identifying small differences between plant groups, or differences in compounds expressed in low concentrations.     

Response to cadmium of Daucus carota hairy roots dual cultures with Glomus intraradices or Gigaspora margarita

Ri T-DNA-transformed carrot roots were cultivated in two experiments either non-inoculated or inoculated with the arbuscular mycorrhizal (AM) fungi Glomus intraradices or Gigaspora margarita. The influence of two concentrations of cadmium (Cd) in the medium (2 mg l^–1, 4 mg l^–1) on both root and mycelium growth was tested. Both parameters were estimated at 10-day intervals for 70 or 100 days for G. intraradices and Gi. margarita, respectively. In the first experiment, G. intraradices showed a rapid spread of extraradical mycelium (ERM) and reached average densities per treatment of about 90 cm cm^–2 agar medium after 70 days. At the higher Cd level, the growth of ERM was delayed in comparison to the treatment without Cd addition. Root growth was inhibited by both Cd levels; the inhibition was, however, significantly lower in the treatments inoculated with G. intraradices compared to the non-inoculated control. In the second experiment, the ERM of Gi. margarita started to grow after a period of 50 days and reached average densities per treatment of only up to 27 cm cm^–2 by the end of the cultivation. The growth of Gi. margarita mycelium was not inhibited by Cd. No differences in root growth were observed between the Gi. margarita inoculated and non-inoculated treatments. The inhibitory effect of Cd on root growth differed between the non-inoculated treatments in both experiments. The study has shown that the AM fungus Glomus intraradices can alleviate Cd-induced growth inhibition to carrot hairy roots. The potential and limits of the monoxenic system in studying the interaction between AM fungi and heavy metals are discussed.     

Mycelium cultivation, chemical composition and antitumour activity of a Tolypocladium sp. fungus isolated from wild Cordyceps sinensis

AIMS: To examine and illustrate the morphological characteristics and growth kinetics of Cs-HK1, a Tolypocladium fungus, isolated from wild Cordyceps sinensis in solid and liquid cultures, and the major chemical constituents and antitumour effects of Cs-HK1 mycelium. METHODS AND RESULTS: The Cs-HK1 fungus was isolated from the fruiting body of a wild C. sinensis and identified as a Tolypocladium sp. fungus. It grew rapidly at 22-25 degrees C on a liquid medium containing glucose, yeast extract, peptone and major inorganic salts, with a specific growth rate of 1.1 day(-1), reaching a cell density of 23.0 g dw l(-1) in 7-9 days. Exopolysaccharides accumulated in the liquid culture to about 0.3 g l(-1) glucose equivalent. In comparison with natural C. sinensis, the fungal mycelium had similar contents of protein (11.7-microg) and carbohydrate (654.6-microg) but much higher contents of polysaccharide (244.2 mg vs 129.5 mg), adenosine (1116.8-microg vs 264.6 microg) and cordycepin (65.7 microg vs 20.8 microg) (per gram dry weight). Cyclosporin A, an antibiotic commonly produced by Tolypocladium sp., was also detected from the mycelium extract. The hot water extract of mycelium showed low cytotoxic effect on B16 melanoma cells in culture (about 25% inhibition) but significant antitumour effect in animal tests, causing 50% inhibition of B16 cell-induced tumour growth in mice. CONCLUSIONS: The Tolypocladium sp. fungus, Cs-HK1, can be easily cultivated by liquid fermentation. The mycelium biomass contained the major bioactive compounds of C. sinensis, and the mycelium extract had significant antitumour activity. SIGNIFICANCE AND IMPACT OF THE STUDY: The Cs-HK1 fungus may be a new and promising medicinal fungus and an effective and economical substitute of the wild C. sinensis for health care.     

Phylogeny of arbuscular mycorrhizal fungi predicts community composition of symbiosis-associated bacteria

Many physicochemical and biotic aspects of the soil environment determine the community composition of bacteria. In this study, we examined the effects of arbuscular mycorrhizal fungi, common symbionts of higher plants, on the composition of bacterial communities after long-term (7-8 years) enrichment culture in the presence of a plant host. We showed that the phylogeny of arbuscular mycorrhizal fungal isolates was a highly significant predictor of bacterial community composition, as assessed by cluster analysis, redundancy analysis and linear discriminant analysis of phospholipid fatty acid patterns. Numerous phospholipid fatty acids differed between the phylogenetic groupings; this pattern also held for fungal-origin phospholipid fatty acids and in a combined bacterial/fungal analysis, suggesting that categorizing phospholipid fatty acids into predominantly bacterial and fungal origin did not affect the overall outcome. The mechanisms underlying this observation could include substrate quality (and quantity) effects, interactions mediated by the host plant (e.g. rhizodeposition) and direct biotic interactions between arbuscular mycorrhizal fungi and bacterial populations. Our results suggest that aspects of arbuscular mycorrhizal fungal functions may be partially explained by the symbiosis-accompanying bacterial communities, a possibility that should be explicitly considered in studies examining the roles of arbuscular mycorrhizal fungal species diversity in soil and ecosystem processes.     

Different native arbuscular mycorrhizal fungi influence the coexistence of two plant species in a highly alkaline anthropogenic sediment

Different species of arbuscular mycorrhizal fungi (AMF) can produce different amounts of extraradical mycelium (ERM) with differing architectures. They also have different efficiencies in gathering phosphate from the soil. These differences in phosphate uptake and ERM length or architecture may contribute to differential growth responses of plants and this may be an important contributor to plant species coexistence. The effects of the development of the ERM of AMF on the coexistence of two co-occurring plant species were investigated in root-free hyphal chambers in a rhizobox experimental unit. The dominant shrub (Salix atrocinerea Brot.) and herbaceous (Conyza bilbaoana J. Rémy) plant species found in a highly alkaline anthropogenic sediment were studied in symbiosis with four native AMF species (Glomus intraradices BEG163, Glomus mosseae BEG198, Glomus geosporum BEG199 and Glomus claroideum BEG210) that were the most abundant members of the AMF community found in the sediment. Different AMF species did not influence total plant productivity (sum of the biomass of C. bilbaoana and S. atrocinerea), but had a great impact on the individual biomass of each plant species. The AMF species with greater extracted ERM lengths (G. mosseae BEG198, G. claroideum BEG210 and the four mixed AMF) preferentially benefited the plant species with a high mycorrhizal dependency (C. bilbaoana), while the AMF species with the smallest ERM length (G. geosporum BEG199) benefited the plant species with a low mycorrhizal dependency (S. atrocinerea). Seed production of C. bilbaoana was only observed in plants inoculated with G. mosseae BEG198, G. claroideum BEG210 or the mixture of the four AMF. Our results show that AMF play an important role in the reproduction of C. bilbaoana coexisting with S. atrocinerea in the alkaline sediment and have the potential to stimulate or completely inhibit seed production. The community composition of native AMF and the length of the mycelium they produce spreading from roots into the surrounding soil can be determinant of the coexistence of naturally co-occurring plant species.     

Ecological aspects of mycorrhizal symbiosis: with special emphasis on the functional diversity of interactions involving the extraradical mycelium

Different symbiotic mycorrhizal associations between plantsand fungi occur, almost ubiquitously, in a wide range of terrestrialecosystems. Historically, these have mainly been consideredwithin the rather narrow perspective of their effects on theuptake of dissolved mineral nutrients by individual plants.More recent research has placed emphasis on a wider, multifunctionalperspective, including the effects of mycorrhizal symbiosison plant and microbial communities, and on ecosystem processes.This includes mobilization of N and P from organic polymers,release of nutrients from mineral particles or rock surfacesvia weathering, effects on carbon cycling, interactions withmyco-heterotrophic plants, mediation of plant responses to stressfactors such as drought, soil acidification, toxic metals, andplant pathogens, as well as a range of possible interactionswith groups of other soil micro-organisms. Mycorrhizal fungiconnect their plant hosts to the heterogeneously distributednutrients required for their growth, enabling the flow of energy-richcompounds required for nutrient mobilization whilst simultaneouslyproviding conduits for the translocation of mobilized productsback to their hosts. In addition to increasing the nutrientabsorptive surface area of their host plant root systems, theextraradical mycelium of mycorrhizal fungi provides a directpathway for translocation of photosynthetically derived carbonto microsites in the soil and a large surface area for interactionwith other micro-organisms. The detailed functioning and regulationof these mycorrhizosphere processes is still poorly understoodbut recent progress is reviewed and potential benefits of improvedunderstanding of mycorrhizosphere interactions are discussed. Key words: Arbuscular mycorrhiza, biotic interactions, carbon flow, ectomycorrhiza, ericoid mycorrhiza, mycelium, nutrient uptake, symbiosis, weathering Received 22 January 2008; Revised 7 February 2008 Accepted 7 February 2008     

牛肝菌液体发酵及产多糖的影响因素研究

牛肝菌(Boletused)属外生菌根菌,美味牛肝菌多糖有明显的抗肿瘤效果。采用液体培养方法对牛肝菌菌丝体的发酵及产多糖特性进行了研究,实验考察了培养基中葡萄糖浓度和培养基的初始pH对牛肝菌菌丝量及产多糖的影响。结果表明,实验条件下,该株牛肝菌在pH值5．5—6．0,葡萄糖含量为60mg/mL时,多糖产量为6．7mg/mL。实验考察了从发酵菌丝体中提取多糖的几种方法,其中研磨法效果较好,与对照相比,多糖提取量增加了20％。     

猪苓营养菌丝与栽培菌核蛋白质成分的分析

对猪苓(Polyporus umbellate)营养菌丝与栽培菌核中蛋白质的氨基酸种类及含量进行了测定。结果表明,猪苓营养菌丝中各物质质量分数是:粗蛋白325.9g·kg-1,必需氨基酸总量34.924 g·kg-1,氨基酸总量91.956 g·kg-1;栽培菌核中各物质质量分数是:粗蛋白49.1 g·kg-1,必需氨基酸总量8.465 g·kg-1,氨基酸总量35.847 g·kg-1。营养菌丝中所含粗蛋白、氨基酸的量显著高于栽培菌核中粗蛋白、氨基酸的量。     

Nutrient transfer from soil nematodes to plants: a direct pathway provided by the mycorrhizal mycelial network

A pathway for the transfer of nutrients from dead nematodes to mycorrhizal plants is described for the first time. Plants of Betula pendula were grown in transparent microcosms in the mycorrhizal (M) or non‐mycorrhizal (NM) condition, either with or without nematode necromass of known nitrogen (N) and phosphorus (P) contents as the major potential source of these elements. Plants colonized by the mycorrhizal fungus Paxillus involutus produced greater yields and had larger N and P contents in the presence of nematodes than did their NM counterparts. The symbiotic systems were shown to exploit the N and P originally contained in necromass more effectively, and to transfer the nutrients to the plants in quantities approximately double those seen in NM systems. Even so, NM plants obtained sufficient N and P from dead nematodes to enable some enhancement of growth. Our observations confirm that mycorrhizal fungi provide the potential for the recycling of nutrients contained in this quantitatively important component of the soil mesofauna and demonstrate that the symbiotic pathway is considerably more effective than that provided by saprotrophs alone. The consequences of this nutrient transfer pathway for nutrient recycling in temperate forest ecosystems are considered.     

The extraradical proteins of Rhizophagus irregularis: A shotgun proteomics approach

Arbuscular Mycorrhizal fungi (AMF, Glomeromycota) form obligate symbiotic associations with the roots of most terrestrial plants. Our understanding of the molecular mechanisms enabling AMF propagation and AMF-host interaction is currently incomplete. Analysis of AMF proteomes could yield important insights and generate hypotheses on the nature and mechanism of AMF-plant symbiosis. Here, we examined the extraradical mycelium proteomic profile of the arbuscular mycorrhizal fungus Rhizophagus irregularis grown on Ri T-DNA transformed Chicory roots in a root organ culture setting. Our analysis detected 529 different peptides that mapped to 474 translated proteins in the R. irregularis genome. R. irregularis proteome was characterized by a high proportion of proteins (9.9 % of total, 21.4 % of proteins with functional prediction) mediating a wide range of signal transduction processes, e.g. Rho1 and Bmh2, Ca-signaling (calmodulin, and Ca channel protein), mTOR signaling (MAP3K7, and MAPKAP1), and phosphatidate signaling (phospholipase D1/2) proteins, as well as members of the Ras signaling pathway. In addition, the proteome contained an unusually large proportion (53.6 %) of hypothetical proteins, the majority of which (85.8 %) were Glomeromycota-specific. Forty-eight proteins were predicted to be surface/membrane associated, including multiple hypothetical proteins of yet-unrecognized functions. However, no evidence for the overproduction of specific proteins, previously implicated in promoting soil health and aggregation was obtained. Finally, the comparison of R. irregularis proteome to previously published AMF proteomes identified a core set of pathways and processes involved in AMF growth. We conclude that R. irregularis growth on chicory roots requires the activation of a wide range of signal transduction pathways, the secretion of multiple novel hitherto unrecognized Glomeromycota-specific proteins, and the expression of a wide array of surface-membrane associated proteins for cross kingdom cell-to-cell communications.