丛枝菌根真菌和根瘤菌对白三叶氮同化的影响

为揭示丛枝菌根真菌(AMF)和根瘤菌在白三叶氮(N)同化中的作用,该研究对白三叶进行单一或联合接种隐类球囊霉(Paraglomus occultum)和三叶草根瘤菌(Rhizobium trifolii),分析其对白三叶的生长、光合作用、叶片N和氨基酸含量以及N同化相关酶活性的影响。结果表明:(1)单一接种AMF或根瘤菌以及联合接种AMF和根瘤菌均显著增加了白三叶的株高、匍匐茎长度、叶片数、地上部生物量、总生物量、叶绿素b和总叶绿素含量、稳态光量子效率和叶片N含量,这种增强效应是联合接种>单一AMF>单一根瘤菌>未接种处理。(2)联合接种AMF和根瘤菌显著增加了白三叶叶片中丙氨酸、精氨酸、天冬酰胺、天冬氨酸、谷氨酰胺、谷氨酸和组氨酸的含量,显著提升了叶片N同化相关酶如硝酸还原酶、亚硝酸还原酶、谷氨酰胺合成酶、谷氨酸合成酶、谷氨酸脱氢酶、天冬酰胺合成酶和天冬氨酸转氨酶的活性,显著促进AMF对白三叶根系的侵染。综上认为,联合接种AMF和根瘤菌通过激活N同化相关酶活性有效促进N同化,产生更多氨基酸,进一步促进白三叶植株生长; 联合接种AMF和根瘤菌具有协同作用,有效促进了白三叶的N同化。     

Effects of prometryn and acetochlor on arbuscular mycorrhizal fungi and symbiotic system

Prometryn and acetochlor are common herbicides widely used to control weeds in agricultural systems. The impacts of the two herbicides on spore germination, hyphal elongation, the biomass and malondialdehyde content of carrot hairy roots were investigated using a strict in vitro cultivation system associating the Ri T‐DNA‐transferred carrot hairy roots with Glomus etunicatum. Alternatively, root colonization, daughter spore production and the proportion of hyphae with succinate dehydrogenase (SDH) and alkaline phosphatase (ALP) activities were also investigated. No significant impact on spore germination was noted in the presence of acetochlor at all three concentrations tested, while a significant decrease was observed with prometryn only at the highest concentration. Moreover, an inverse correlation was identified between herbicides concentrations and G. etunicatum root colonization and spore production as well as hyphal SDH and ALP activity, with a positive correlation identified among these four factors. Both herbicides exerted negative effects on the arbuscular mycorrhizal (AM) fungus and symbiosis at increasing concentrations, with prometryn apparently more toxic than acetochlor. Furthermore, the AM symbiotic system was shown to improve biomass, reduce malondialdehyde accumulation and ease lipid peroxidation in carrot hairy roots and decrease damage in host plants, thus enhancing plant tolerance to adverse conditions.

Significance and Impact of the Study

In this study, the effect of prometryn and acetochlor on the physiology and metabolic activities of the AM fungus Glomus etunicatum were investigated. Our findings demonstrate for the first time, the impact of the two herbicides at three concentrations (0·1, 1 and 10 mg l^?1) on transformed carrot hairy roots/AM fungus association under strict in vitro culture conditions, which may guide the application of the two herbicides in modern agriculture.     

云南杓兰菌根真菌组成及共生关系研究

杓兰属(Cypripedium)植物因具有较高的观赏和药用价值而长期被过度采集,已成为濒危植物。利用菌根技术进行杓兰属植物的保护和人工栽培,需要获得其可培养的菌根真菌。该研究采用分离培养法和共生回接方法,研究了云南杓兰菌根真菌菌群组成及其共生关系。结果表明:(1)从10株云南杓兰300块毛根组织中分离获得126株内生真菌,归属为3个菌属,分别是胶膜菌属(Tulasnella)73株、伏革菌属(Corticium)36株、角担菌属(Ceratobasidium)17株。其中,胶膜菌属为优势菌群,占总菌株数量的57.94%。(2)6株供试菌株中,4株菌株可显著缩短种子的萌发过程,6株菌株对幼苗的生长有显著的促进作用。(3)从中筛选获得一株CY-18高效促生真菌,对云南杓兰种子共生萌发和幼苗共生生长有极显著的促进作用。该研究结果为更好地利用菌根技术进行杓兰属植物资源的保护与可持续利用奠定了基础。     

Evolutionary histories and mycorrhizal associations of mycoheterotrophic plants dependent on saprotrophic fungi

Mycoheterotrophic plants (MHPs) are leafless, achlorophyllous, and completely dependent on mycorrhizal fungi for their carbon supply. Mycorrhizal symbiosis is a mutualistic association with fungi that is undertaken by the majority of land plants, but mycoheterotrophy represents a breakdown of this mutualism in that plants parasitize fungi. Most MHPs are associated with fungi that are mycorrhizal with autotrophic plants, such as arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi. Although these MHPs gain carbon via the common mycorrhizal network that links the surrounding autotrophic plants, some mycoheterotrophic lineages are associated with saprotrophic (SAP) fungi, which are free-living and decompose leaf litter and wood materials. Such MHPs are dependent on the forest carbon cycle, which involves the decomposition of wood debris and leaf litter, and have a unique biology and evolutionary history. MHPs associated with SAP fungi (SAP-MHPs) have to date been found only in the Orchidaceae and likely evolved independently at least nine times within that family. Phylogenetically divergent SAP Basidiomycota, mostly Agaricales but also Hymenochaetales, Polyporales, and others, are involved in mycoheterotrophy. The fungal specificity of SAP-MHPs varies from a highly specific association with a single fungal species to a broad range of interactions with multiple fungal orders. Establishment of symbiotic culture systems is indispensable for understanding the mechanisms underlying plant–fungus interactions and the conservation of MHPs. Symbiotic culture systems have been established for many SAP-MHP species as a pure culture of free-living SAP fungi is easier than that of biotrophic AM or ECM fungi. Culturable SAP-MHPs are useful research materials and will contribute to the advancement of plant science.

     

Measuring the fitness of symbiotic rhizobia

The legume-rhizobia symbiosis is an important model system for research on the evolution of cooperation and conflict. A key strength of this system is that the fitness consequences of greater or lesser investment in cooperative behaviors can be measured for each partner. Most empirical studies have characterized the fitness of symbiotic rhizobia exclusively by their numbers within nodules, often estimated using nodule size as a proxy. Here we show that the relationship between nodule size and rhizobial numbers can differ drastically between strains of the same species. We further show that differences in accumulation of the storage polyester poly-3-hydroxybutyrate (PHB), which can support future reproduction, can be large enough that even direct measurements of rhizobial numbers alone can lead to qualitatively incorrect conclusions. Both results come from a comparison of strains differing in production of the ethylene-inhibitor rhizobitoxine (Rtx). A broader study (using three legume-rhizobia species pairs) showed that PHB/cell cannot be reliably estimated from its correlation with rhizobia/nodule or nodule size. Differences in PHB between strains or treatments will not always make major contributions to differences in fitness, but situation-specific data are needed before PHB can safely be neglected.     

Nuclei of symbiotic arbuscular mycorrhizal fungi as revealed by in vivo two-photon microscopy

The present work reports the results obtained from in vivo studies on the distribution and behavior of nuclei of two arbuscular mycorrhizal (AM) fungi growing in symbiosis with tomato root organ cultures (AM monoxenic cultures). Upon staining with 4',6-diamidino-2-phenylindole and two-photon microscopy (2PM) observations, symbiotic thick runner hyphae appeared mostly opaque to 2PM and did not reveal nuclei within them; thin runner hyphae showed dimly stained nuclei along them, whereas nuclei were clearly visible within the branches of the so-called branched absorbing structures. When visible, nuclei appeared anchored laterally at regular intervals along the symbiotic AM extraradical hyphae. Other nuclei migrate through the hyphal central core; this migration occurs in pulses. Simultaneous observations on different areas of extraradical AM mycelium revealed the existence of lysed compartments along the fungal hyphae, containing nuclei remnants and/or chromatin masses. All these results give new insights in (i) the differential permeability of AM hyphae in the symbiotic versus the asymbiotic state; (ii) the behavior and distribution of nuclei along the symbiotic extraradical mycelium; (iii) the occurrence of ageing events within the AM fungal colony; and (iv) the existence of "healing" mechanisms aiming to restrict the damage induced by such ageing or lytic events. An AM fungal strategy for hyphal survival under adverse conditions is also suggested.     

Nuclei of symbiotic arbuscular mycorrhizal fungi as revealed by in vivo two-photon microscopy

Summary The present work reports the results obtained from in vivo studies on the distribution and behavior of nuclei of two arbuscular mycorrhizal (AM) fungi growing in symbiosis with tomato root organ cultures (AM monoxenic cultures). Upon staining with 4′,6-diamidino-2-phenylindole and two-photon microscopy (2PM) observations, symbiotic thick runner hyphae appeared mostly opaque to 2PM and did not reveal nuclei within them; thin runner hyphae showed dimly stained nuclei along them, whereas nuclei were clearly visible within the branches of the so-called branched absorbing structures. When visible, nuclei appeared anchored laterally at regular intervals along the symbiotic AM extraradical hyphae. Other nuclei migrate through the hyphal central core; this migration occurs in pulses. Simultaneous observations on different areas of extraradical AM mycelium revealed the existence of lysed compartments along the fungal hyphae, containing nuclei remnants and/or chromatin masses. All these results give new insights in (i) the differential permeability of AM hyphae in the symbiotic versus the asymbiotic state; (ii) the behavior and distribution of nuclei along the symbiotic extraradical mycelium; (iii) the occurrence of ageing events within the AM fungal colony; and (iv) the existence of “healing” mechanisms aiming to restrict the damage induced by such ageing or lytic events. An AM fungal strategy for hyphal survival under adverse conditions is also suggested.     

Why are mycorrhizal fungi and symbiotic nitrogen-fixing bacteria not genetically integrated into plants?

The bacteria and fungi involved in diazotrophic and mycorrhizal symbioses with plants have varying degrees of genetic recombination. Those with very limited, or no, recombination are at risk from the progressive accumulation of mutations (‘Müller's ratchet'). This accumulation could be alleviated by complete genetic integration of the parts of the symbiont genomes relating to their function in hospice (nitrogen fixation and acquisition of a range of nutrients, respectively) into the nuclear genome of the (usually) sexually reproducing exhabitant. This integration is not known to have occurred, and the diazotrophic and mycorrhizal inhabitants with very restricted recombination survive ‘Müller's ratchet', as do some other symbioses, free-living organisms that have reproduced asexually for many generations and the organelle genomes of mitochondria and plastids. An evolutionary and environmental possibility is that it was difficult to maintain genetically integrated diazotrophs and mycorrhizas as environments changed with respect to the availability of combined nitrogen and of phosphorus. Genetic modification techniques could be used to attempt to genetically integrate diazotrophs and mycorrhizas; even granted that this could be done, a careful evaluation is required of whether the benefits of such manipulation outweigh whatever costs are entailed.     

网络分析在宿主植物与菌根真菌共生关系研究中的应用

菌根共生体是生物界最广泛的互惠共生体,共生关系多样性是生物多样性的重要组成部分,当前群落尺度菌根共生关系研究才刚刚起步,但发展迅速。网络分析作为生态学研究的重要手段逐渐在菌根共生关系中得以应用,网络分析为群落尺度探究菌根真菌多样性分布规律、共生机制研究提供新观点和途径,对菌根真菌群落结构、生态功能研究具有重要意义。本文总结了网络分析方法在单点式、双点式和多点式菌根共生关系网络研究中的优势和局限性,同时还阐述了零模型选择和构建网络大小对关系网络度量指数的影响,为菌根真菌群落结构、生态功能研究提供新思路,为后续群落尺度菌根共生关系格局研究提供借鉴。     

丛枝菌根真菌与放线菌对辣椒和茄子的促生防病效应

丛枝菌根真菌(AMF)和植物共生放线菌(PSA)具有促进植物生长、抑菌、抗逆和防病等作用.然而,AMF与PSA之间是否能协同发挥促生防病作用值得探究.本试验旨在评价AMF和PSA对茄科蔬菜的促生防病效应,获得高效AMF+PSA组合.温室盆栽试验采用辣椒(羊角椒)和茄子(黑冠长茄子),分别接种和不接种AMF摩西斗管囊霉(Fm)、变形球囊霉(Gv)、PSA浑圆链霉菌(H6-1)、娄彻氏链霉菌(S2-2)、珊瑚链霉菌(D11-4)和病原真菌灰葡萄孢,共48个处理,测定各处理植株生长、发病和根系共生体发育状况等.结果表明: Fm与PSA能相互促进侵染定殖,而Gv与PSA相互抑制.与不接种对照相比,接种AMF、PSA和AMF+PSA各处理均能不同程度地提高辣椒和茄子植株的光合性能、根系活力和生长量.接种病原真菌条件下,接种AMF和PSA处理均显著促进植株生长,降低植株的病情指数,其中,PSA的促生防病效应大于AMF,Fm+H6-1组合对辣椒的促生防病效果最好,对灰霉病的防效达69.1%;Fm+D11-4对茄子的促生防病效果最佳,对灰霉病的防效达75.5%.在本试验条件下,Fm+H6-1和Fm+D11-4分别是辣椒和茄子促生防病的高效组合,有待进一步开展田间试验.     

Comparing symbiotic performance and physiological responses of two soybean cultivars to arbuscular mycorrhizal fungi under salt stress

The presented experiments evaluated the symbiotic performance of soybean genotypes with contrasting salt stress tolerance to arbuscular mycorrhizal fungi (AMF) inoculation. In addition, the physiological stress tolerance mechanisms in plants derived from mutualistic interactions between AMF and the host plants were evaluated. Plant growth, nodulation, nitrogenase activity and levels of endogenous growth hormones, such as indole acetic acid and indole butyric acid, of salt-tolerant and salt-sensitive soybean genotypes significantly decreased at 200 mM NaCl. The inoculation of soybean with AMF improved the symbiotic performance of both soybean genotypes by improving nodule formation, leghemoglobin content, nitrogenase activity and auxin synthesis. AMF colonization also protected soybean genotypes from salt-induced membrane damage and reduced the production of hydrogen peroxide, subsequently reducing the production of TBARS and reducing lipid peroxidation. In conclusion, the results of the present investigation indicate that AMF improve the symbiotic performance of soybean genotypes regardless of their salt stress tolerance ability by mitigating the negative effect of salt stress and stimulating endogenous level of auxins that contribute to an improved root system and nutrient acquisition under salt stress.     

春兰菌根真菌CL-3菌株的鉴定及共生体系的构建

采用分离自野生春兰(Cymbidium goeringii)根部的真菌CL-3菌株, 进行了春兰内生菌根真菌的人工接种、再分离及其共生培养研究。通过对CL-3菌株形态学观察和ITS序列同源性分析, 发现该菌株ITS序列与Acremonium strictum的亲缘关系最为接近, 序列同源性为100%。用CL-3菌株接种春兰组培苗, 接种后2个月可从组培苗中再分离获得该菌株, 且CL-3菌株处理苗的鲜重增长率达80.5%, 经方差分析, 与对照相比有显著差异。通过石蜡切片和染色, 在已接种的组培苗的根部组织中可观察到CL-3菌株存在。表明CL-3菌株能与组培幼苗成功建立共生培养体系。     

混合盐碱胁迫下接种丛枝菌根真菌和根瘤菌对紫花苜蓿生长的影响

随着气候变化,全球土壤盐碱化严重威胁着农牧业生产和生态环境的建设。土壤盐化与碱化常常伴随发生,目前多数研究侧重于盐胁迫,忽略了碱胁迫的存在。实际上,碱性盐除了盐度外还伴随着高p H。由此,试图探讨混合盐碱胁迫下接种丛枝菌根真菌(AMF)和根瘤菌对紫花苜蓿生长的影响及其作用机理。根据中国盐碱地的特点,将4种盐(Na Cl、Na_2SO_4、Na_2CO_3、Na HCO_3)按一定比例混合模拟出16种混合盐碱(盐浓度25—150 mmol/L,p H 7.67—10.52)胁迫浓度,按照L_(16)(16~1×2~2)混合正交设计,采用盆栽法研究了混合盐碱胁迫下接种AMF摩西管柄囊霉(Funneliformis mosseae)和根瘤菌(Sinorhizobium meliloti)对紫花苜蓿生长及生理的影响。结果表明:对紫花苜蓿株高的影响程度依次是AMF+根瘤菌pHAMF盐碱类型根瘤菌;对地上生物量、地下生物量、茎高净增长量、丙二醛(MDA)及脯氨酸影响程度依次是p HAMF+根瘤菌盐碱类型AMF根瘤菌;对超氧化物歧化酶(SOD)的影响程度依次是p HAMF+根瘤菌盐碱类型AMF根瘤菌;对过氧化物酶(POD)影响程度依次是p HAMF+根瘤菌根瘤菌AMF盐碱类型;对蛋白质的影响程度依次是p H盐碱类型根瘤菌AMF+根瘤菌=AMF。株高、地下生物量、POD均在双接种的处理下出现最大值。本研究证明:盐碱混合胁迫会严重抑制植物的生长发育;而接种AMF和/或根瘤菌均可有效缓解盐碱胁迫对植物造成的伤害,提高植物对盐碱的耐受能力;且同时接种AMF及根瘤菌效果最好,其次是单独接种AMF,单独接种根瘤菌作用相对最小。     

The interactions between plant life form and fungal traits of arbuscular mycorrhizal fungi determine the symbiotic community

Arbuscular mycorrhizal (AM) fungi have traditionally been considered generalist symbionts. However, an increasing number of studies are pointing out the selectivity potential of plant hosts. Plant life form, determined by plant life history traits, seems to drive the AM fungal community composition. The AM fungi also exhibit a wide diversity of functional traits known to be responsible for their distribution in natural ecosystems. However, little is known about the role of plant and fungal traits driving the resultant symbiotic assemblages. With the aim of testing the feedback relationship between plant and fungal traits on the resulting AM fungal community, we inoculated three different plant life forms, i.e. annual herbs, perennial herbs and perennial semi-woody plants, with AM fungal communities sampled in different seasons. We hypothesized that the annual climate variation will induce changes in the mean traits of the AM fungal communities present in the soil throughout the year. Furthermore, the association of plants with different life forms with AM fungi with contrasting life history traits will show certain preferences according to reciprocal traits of the plants and fungi. We found changes in the AM fungal community throughout the year, which were differentially disrupted by disturbance and altered by plant growth form and plant biomass. Both plant and fungal traits clearly contributed to the resultant AM fungal communities. The revealed process can have implications for the functioning of ecosystems since changes in dominant plant life forms or climatic variables could influence the traits of AM fungal communities in soil and hence ecosystem processes.     

Response to paclobutrazol of symbiotic mycorrhizal fungi and dropper (tuber stalk) formation of host orchid seedlings

The effects of the triazole compound paclobutrazol on the mycorrhizalfungi and production of droppers (tuber stalks) in three species of terrestrialorchids of southwestern Australia were investigated. Seedlings ofDiuris laxiflora Lindley (bee orchid), Microtismedia R. Br. (common mignonette orchid), and Pterostylissanguinea D. Jones & M. Clements (dark banded greenhood orchid)were cultured symbiotically with specific mycorrhizal fungi invitro. The mycorrhizal fungi of the study species were grown on mediacontaining paclobutrazol at 0, 1.7, 3.4, 10.2, or 17.0 M(corresponding to 0, 0.5, 1.0, 3.0, or 5.0 mgL^–1). Paclobutrazol at all concentrations evaluateddecreased the growth rates of the mycorrhizal fungi of M.media and P. sanguinea below that of thecontrol. However, paclobutrazol did not adversely affect the growth of themycorrhizal fungus of D. laxiflora, and low concentrations(1.7 or 3.4 M) stimulated the growth of this fungus. Symbiotic seedlings of the study species were exposed to paclobutrazolat 0, 1.7, 3.4, 10.2, or 17.0 M. Paclobutrazol at allconcentrations evaluated increased dropper (tuber stalk) production inD. laxiflora, but had no effect on M.media and P. sanguinea.This suggests that, for species in which paclobutrazol has no fungicidaleffect on mycorrhizal fungi, it has the potential to stimulate early andefficient tuberization of symbiotic orchid seedlings.     

Genomics of parasitic and symbiotic fungi

Complete and partial genome sequence information is underway in several parasitic and symbiotic fungi that infect humans, other animals and plants. Comparative analyses of these sequences will provide new insights into the genomic plasticity and evolution of parasitism and mutualism in fungi.     

丛枝菌根（AM）真菌-豆科植物-根瘤菌共生识别信号研究概况

<正>植物与微生物共生是自然界中普遍存在的一种生物学现象,其中高等植物和丛枝菌根(arbuscular mycorrhiza,AM)真菌共生形成的菌根、以及豆科植物和根瘤菌(rhizobia)形成的根瘤与农林牧业生产和生态系统的稳定性密切相关。豆科植物形成根瘤的同时还能与AM真菌形成菌根,最终建立三位一体     

独花兰菌根真菌的分离及rDNA ITS序列在其分类鉴定中的应用

独花兰(Changnienia amoena Chien)为我国特有的独属独种兰科植物,仅生长于长江中下游及陕西南部的山地林下及沟谷中,是中国特有兰科物种之一,被列为国家二级保护植物.以浙江天目山自然保护区的野生独花兰中分离获得的菌根真菌为对象,应用传统的形态结构鉴别与rDNA ITS分子生物学手段相结合的研究方法,进行了菌株的分类鉴定研究,确定该菌株为兰科菌根真菌之一的胶膜菌属(Tulasnella)真菌.研究结果对于全面了解兰科植物菌根真菌的特征和有效保护独花兰植物资源均具较大意义和参考价值.