内蒙古露天煤矿区回填土壤具生态适应能力丛枝菌根真菌的筛选

在盆栽试验条件下,应用灭菌的露天煤矿区回填土壤为培养基质,研究8个丛枝菌根真菌菌种(株)对沙打旺生长及根系侵染的影响.结果表明,分离自江西和新疆的Glomus mosseae的2个菌株在露天煤矿区回填土壤上能够显著提高沙打旺的生物量,并能有效改善植株的磷、氮营养;其侵染率均在50%以上,且根外繁殖体数显著高于其他接种处理.说明此两个菌株在该土壤上具有良好的生态适应能力,有助于露天煤矿区植被重建和生态恢复等研究工作的进一步开展.     

Metabolite profiling of mycorrhizal roots of Medicago truncatula

Metabolite profiling of soluble primary and secondary metabolites, as well as cell wall-bound phenolic compounds from roots of barrel medic (Medicago truncatula) was carried out by GC-MS, HPLC and LC-MS. These analyses revealed a number of metabolic characteristics over 56 days of symbiotic interaction with the arbuscular mycorrhizal (AM) fungus Glomus intraradices, when compared to the controls, i.e. nonmycorrhizal roots supplied with low and high amounts of phosphate. During the most active stages of overall root mycorrhization, elevated levels of certain amino acids (Glu, Asp, Asn) were observed accompanied by increases in amounts of some fatty acids (palmitic and oleic acids), indicating a mycorrhiza-specific activation of plastidial metabolism. In addition, some accumulating fungus-specific fatty acids (palmitvaccenic and vaccenic acids) were assigned that may be used as markers of fungal root colonization. Stimulation of the biosynthesis of some constitutive isoflavonoids (daidzein, ononin and malonylononin) occurred, however, only at late stages of root mycorrhization. Increase of the levels of saponins correlated AM-independently with plant growth. Only in AM roots was the accumulation of apocarotenoids (cyclohexenone and mycorradicin derivatives) observed. The structures of the unknown cyclohexenone derivatives were identified by spectroscopic methods as glucosides of blumenol C and 13-hydroxyblumenol C and their corresponding malonyl conjugates. During mycorrhization, the levels of typical cell wall-bound phenolics (e.g. 4-hydroxybenzaldehyde, vanillin, ferulic acid) did not change; however, high amounts of cell wall-bound tyrosol were exclusively detected in AM roots. Principal component analyses of nonpolar primary and secondary metabolites clearly separated AM roots from those of the controls, which was confirmed by an hierarchical cluster analysis. Circular networks of primary nonpolar metabolites showed stronger and more frequent correlations between metabolites in the mycorrhizal roots. The same trend, but to a lesser extent, was observed in nonmycorrhizal roots supplied with high amounts of phosphate. These results indicate a tighter control of primary metabolism in AM roots compared to control plants. Network correlation analyses revealed distinct clusters of amino acids and sugars/aliphatic acids with strong metabolic correlations among one another in all plants analyzed; however, mycorrhizal symbiosis reduced the cluster separation and enlarged the sugar cluster size. The amino acid clusters represent groups of metabolites with strong correlations among one another (cliques) that are differently composed in mycorrhizal and nonmycorrhizal roots. In conclusion, the present work shows for the first time that there are clear differences in development- and symbiosis-dependent primary and secondary metabolism of M. truncatula roots.     

Arbuscular mycorrhizal fungal propagules in a salt marsh

The tolerance of indigenous arbuscular mycorrhizal fungi (AMF) to stressful soil conditions and the relative contribution of spores of these fungi to plant colonization were examined in a Portuguese salt marsh. Glomus geosporum is dominant in this salt marsh. Using tetrazolium as a vital stain, a high proportion of field-collected spores were found to be metabolically active at all sampling dates. Spore germination tests showed that salt marsh spores were not affected by increasing levels of salinity, in contrast to two non-marsh spore isolates, and had a significantly higher ability to germinate under increased levels of salinity (20) than in the absence of or at low salinity (10). Germination of salt marsh spores was not affected by soil water levels above field capacity, in contrast to one of the two non-marsh spore isolates. For the evaluation of infectivity, a bioassay was established with undisturbed soil cores (containing all types of AM fungal propagules) and soil cores containing only spores as AM fungal propagules. Different types of propagules were able to initiate and to expand the root colonization of a native plant species, but spores were slower than mycelium and/or root fragments in colonizing host roots. The AM fungal adaptation shown by this study may explain the maintenance of AMF in salt marshes.     

Belowground biodiversity effects of plant symbionts support aboveground productivity

Soil microbes play key roles in ecosystems, yet the impact of their diversity on plant communities is still poorly understood. Here we demonstrate that the diversity of belowground plant-associated soil fungi promotes plant productivity and plant coexistence. Using additive partitioning of biodiversity effects developed in plant biodiversity studies, we demonstrate that this positive relationship can be driven by complementarity effects among soil fungi in one soil type and by a selection effect resulting from the fungal species that stimulated plant productivity the most in another soil type. Selection and complementarity effects among fungal species contributed to improving plant productivity up to 82% and 85%, respectively, above the average of the respective fungal species monocultures depending on the soil in which they were grown. These results also indicate that belowground diversity may act as insurance for maintaining plant productivity under differing environmental conditions.     

Fish models in prion biology: Underwater issues

Transmissible spongiform encephalopathies (TSEs), otherwise known as prion disorders, are fatal diseases causing neurodegeneration in a wide range of mammalian hosts, including humans. The causative agents - prions - are thought to be composed of a rogue isoform of the endogenous prion protein (PrP). Beyond these and other basic concepts, fundamental questions in prion biology remain unanswered, such as the physiological function of PrP, the molecular mechanisms underlying prion pathogenesis, and the origin of prions. To date, the occurrence of TSEs in lower vertebrates like fish and birds has received only limited attention, despite the fact that these animals possess bona fide PrPs. Recent findings, however, have brought fish before the footlights of prion research. Fish models are beginning to provide useful insights into the roles of PrP in health and disease, as well as the potential risk of prion transmission between fish and mammals. Although still in its infancy, the use of fish models in TSE research could significantly improve our basic understanding of prion diseases, and also help anticipate risks to public health. This article is part of a Special Issue entitled Zebrafish Models of Neurological Diseases.     

A short LysM protein with high molecular diversity from an arbuscular mycorrhizal fungus,Rhizophagus irregularis

Arbuscular mycorrhizal (AM) fungi form an intimate symbiosis with roots of more than 80% of land plants without eliciting a significant defense response, and how they do so is yet to be determined. Typically, plants mount a defense response upon sensing chitin in fungal walls, and to counteract this response, plant-pathogenic fungi secrete small effector proteins with chitin-binding LysM domains. In the AM fungus, Rhizophagus irregularis, a small, putatively-secreted LysM protein, which we refer to as RiSLM, is among the most highly expressed effector-like proteins during symbiosis. Here, we show that RiSLM expression is reduced during non-functional symbiosis with Medicago mutants, mtpt4-2 and vapyrin. We demonstrate that RiSLM can bind to both chitin and chitosan, and we model the protein-ligand interaction to identify possible binding sites. Finally, we have identified RiSLM homologs in five published R. irregularis isolate genomes and demonstrate that the gene is subject to a high rate of evolution and is experiencing positive selection, while still conserving putative function. Our results present important clues for elucidating a role for a LysM effector, RiSLM, in AM symbiosis.     

山东省不同植被区内野生植物根围AM菌的生态分布

ＡＭ菌是土壤习居菌 ,生态适应性强 ,可发生在各种生态环境。寄主范围也十分广泛 ,除少量植物如莎草科、苋科、灯心草科、藜科、石竹科等 2 0余科植物不能或不易形成ＡＭ外 ,大多数植物包括苔藓、蕨类、裸子植物、被子植物都能被菌根菌侵染。当前人们十分重视对野生植物上ＡＭ菌的调查[3 ,4 ,1 0 ,1 1 ,1 4 ]。研究发现 ,野生植物上可能有比栽培作物更多的ＡＭ菌种类[1 ]。我国野生植物资源丰富 ,开发和利用野生寄主植物上的ＡＭ菌潜力巨大。由于ＡＭ菌对寄主植物的选择性及对环境条件的适应性不同 ,或进化过程中的历史原因 ,造成了自然生态…     

Mycorrhizal‐mediated nitrogen acquisition in switchgrass under elevated temperatures and N enrichment

Arbuscular mycorrhizal fungi (AMF) can perform key roles in ecosystem functioning through improving host nutrient acquisition. Nitrogen (N) is an essential nutrient for plant growth, however, anthropogenic N loading (e.g. crop fertilization and deposition from combustion sources) is increasing so that N now threatens ecosystem sustainability around the world by causing terrestrial and aquatic eutrophication and acidification. It is important to better understand the capacity of AMF to directly uptake N from soils and transfer it to host plants because this process may increase N recycling and retention within ecosystems. In addition to understanding the role of AMF in the N cycle in the present day it is important to understand how AMF function may change as global change proceeds. Currently the net effects of N enrichment and elevated temperature predicted with global change on AMF are unknown. In this study, we examined the effects of N enrichment by simulated N‐deposition loading, elevated temperatures expected by future global changes and their interactions on growth and AMF‐mediated N acquisition of switchgrass (Panicum virgatum var. Alamo), an important species for biofuel production. Switchgrass plants were grown in microcosm units that divided mycorrhizal roots from AMF hyphae and organic residues enriched with ¹⁵N by compartments separated by an air gap to reduce N diffusion. While AMF did not enhance switchgrass biomass, mycorrhizas significantly increased ¹⁵N in shoots and total shoot N. Neither N enrichment nor elevated temperatures influenced this mycorrhizal‐mediated N uptake and transfer. Results from this study can aid in developing sustainable bioethanol and switchgrass production practices that are less reliant on synthetic fertilizers and more dependent on internal N recycling from AMF.