丛枝菌根真菌与根围促生细菌相互作用的效应与机制

丛枝菌根(arbuscular mycorrhiza,AM)真菌是植物活体营养专性共生菌,广泛存在于陆地各生态系统中.研究表明,AM真菌与根围促生细菌(plant growth promoting rhizobacteria,PGPR)之间的相互作用,尤其是它们之间的协同作用不仅影响植物养分吸收利用、病原物发生发展、土壤理化特性与生物修复等,而且对于可持续农、林、牧业生产、稳定生态系统都具有十分重要的意义.因此,近年来给予众多关注和研究.综述了AM真菌与PGPR之间的相互影响及其可能的作用机制,以及AM真菌与PGPR协同改善植物营养和生长、协同抑制病原菌、协同修复土壤方面的作用,旨在总结AM真菌与PGPR相互作用的效应与机制方面的最新研究进展,为今后研究发展提供依据.     

丛枝菌根真菌与植食性昆虫的相互作用

丛枝菌根(arbuscular mycorrhizal AM)真菌与昆虫均是陆地生态系统中的重要组分,同植物关系密切,对植物的影响和作用是巨大的。生态系统中则以AM真菌-植物-昆虫互作体系参预食物网与生态过程。早在20世纪80年代,人们已开始研究AM真菌对昆虫的影响。进入21世纪人们越来越重视AM真菌与昆虫的相互作用。总结了AM真菌对昆虫取食偏好、生长、繁殖和对植物危害等方面的影响、以及昆虫对AM真菌侵染、扩展和产孢的影响;分析了植物营养状况、昆虫性别、昆虫龄期和AM真菌种类等对AM真菌与昆虫相互作用的影响特点;探讨了AM真菌与昆虫相互作用的机制;展望了利用AM真菌抑制植食性害虫、及促进天敌昆虫和部分传粉昆虫作用的可能性,旨在丰富菌根学研究内容、促进AM真菌与昆虫互作领域的深入研究、为探索生物防控农林业害虫的新途径提供依据。     

菌根真菌是唱响生物共生交响曲的主角——菌根真菌专辑序言

地球上任何生物都不是单独进行生命活动和进化的,即生物之间更多的是依靠密切联合、共生互助、需求互补和共同发展。其中,陆地生态系统中的强大分解者真菌和强大生产者植物关系密切,特别是以菌根真菌(mycorrhizal fungi)为代表的植物共生真菌自始至终与植物共生,这一强-强共生联合在维持生态平衡、保存生态系统可持续生产力与生态系统综合服务功能体系中,其分布之广、作用之多、功能之强和贡献之大,可谓名副其实的生物共生体系中的主导者。近年来,中国在真菌与植物共生研究领域成绩斐然,占据世界重要地位。本期《菌物学报》"菌根真菌专刊"刊登了2篇综述和20篇研究报告。综述分别对丛枝菌根(AM)真菌在煤矿区生态修复应用研究和兰科植物与菌根真菌的营养关系进行了总结和热点论述;研究报告分别对菌物界球囊菌门AM真菌全球公认种的中文学名给予了全面规范正确的描述、对中国部分林区红桦外生菌根真菌多样性、华山松印度块菌菌根中的块菌交配型基因、AM真菌对枳吸收磷和分泌磷酸酶的影响、转Bt基因棉叶片腐熟物抑制AM真菌定殖及菌根对磷的吸收、低pH影响AM真菌丛枝发育和磷的吸收、接种AM真菌与间作对红壤上玉米和大豆种间氮素竞争的影响、AM真菌及其菌种组合对植物根结线虫病害的影响以及接种AM真菌和施加铁可协同降低水稻砷累积等方面进行了研究。本期内容基本体现了中国菌根真菌分类、物种多样性、生理学、生态学、生理生态效应与作用机制研究的最新进展,对当前和今后开展植物共生真菌的研究具有重要的引领作用。     

丛枝菌根真菌诱导植物信号物质研究进展

丛枝菌根(AM)真菌侵染植物根系形成菌根共生体过程中能诱导植物合成多种信号物质,如水杨酸(SA)、茉莉酸(JA)、类黄酮、一氧化氮(NO)和过氧化氢(H2O2)等。这些信号分子的传导途径和作用机制备受关注。本文从AM真菌诱导植物信号物质的种类和数量入手,探讨这些信号分子在植物体内的传导途径、生理效应和可能的作用机制,旨在为研究AM真菌与植物之间的共生关系、功能与进化等提供依据。     

丛枝菌根结构与功能研究进展

丛枝菌根(arbuscular mycorrhiza,AM)是陆地生态系统中分布最广泛、最重要的互惠共生体之一,对提高植物抗逆性、修复污染生境、保持生态系统稳定与可持续生产力的作用显著.AM结构特征是判断菌根形成的主要指标,与其功能密切相关.本文总结了AM丛枝结构、泡囊结构、菌丝结构和侵入点结构等发育特征;分析了A型丛枝结构、P型丛枝结构、泡囊结构和根外菌丝结构与促进寄主植物养分吸收和生长、提高植物抗旱性、耐涝性、耐盐性、抗高温、拮抗病原物、提高植物抗病性、抗重金属毒性、分解有毒有机物、修复污染与退化土壤等功能的关系,及其所发挥的重要作用;探讨了影响AM结构与功能的因子,以及基于AM不同结构所发挥功能的作用机制.旨在为系统研究AM真菌发育特征、AM真菌效能机制,以及评价和筛选AM真菌高效菌种提供依据.     

丛枝菌根真菌脂类代谢对共生信号调控的响应和反馈

丛枝菌根(AM)真菌是自然生态系统中分布最为广泛的真菌之一,在自然界物质循环和能量流动中发挥着重要作用。经过长期的协同进化,AM真菌和宿主植物之间形成了完美的互惠互利的共生关系,而真菌的脂类代谢可能是揭示共生秘密的关键所在。本文综述了AM真菌脂类代谢在共生关系建立和维持中关键作用的最新研究进展,重点探讨了AM真菌脂类代谢对共生信号调控的响应和反馈机制,主要包括:AM真菌脂类存储和释放对共生和非共生状态的响应,以及脂类代谢产物变化与共生营养传递之间的关系;脂类分解过程在共生建立初期对信号分子调控发生的响应,以及相应的物质转化和能量代谢;菌根共生互惠互利关系维持中,真菌脂类代谢与信号分子交流通道的相互渗透和影响。本文对于理解菌根共生机制,促进菌根在生产中的应用具有促进作用。     

外生菌根共生:共生真菌多样性及菌根形成的分子机制

大约2%的维管植物能够与17～18个目约280个属的真菌形成外生菌根关系.外生菌根关系的形成、宿主植物的专一化和宿主转移等事件可能是共生真菌物种分化的重要驱动力.比较基因组学研究发现,外生菌根真菌丢失了大量与植物细胞壁物质降解相关的基因.在外生菌根形成过程中,真菌与宿主植物之间借助多样化的信号分子完成相互识别,并且外生菌根真菌能够借助分泌效应蛋白抑制宿主植物的防御反应,促进菌根形成.本文对外生菌根真菌的多样性和分布规律,以及外生菌根形成的分子机制等方面进行了综述,并据此对后续研究提出展望.     

丛枝菌根(AM)对根瘤菌趋化作用研究

对紫穗槐非接种(AM- Rh-)、单接种根瘤菌(Rh )、单接种AM真菌(AM )和双接种(AM Rh )处理,研究AM真菌、根瘤茵对宿主植物紫穗槐侵染情况,并采用经过改良的根部微生物趋化试验手段研究AM真菌侵染根系后分泌物对根瘤茵的趋化性.实验结果表明:在接种AM Rh 情况下,使宿主先于AM ,Rh '处理形成根瘤,且双接种能够显著提高菌根侵染率;在共生体形成期间,AM真菌与根瘤菌之间存在着识别互动反应和一定的信号物质,接种AM真菌对根瘤菌有正趋化作用;同时,外界温度对AM真菌.宿主植物一根瘤茵三者共生体初始信号识别也起到一定的调控作用.     

同位素示踪技术在丛枝菌根真菌生态学研究中的应用

丛枝菌根(arbuscular mycorrhizal,AM)真菌是生态系统中重要的土壤微生物之一。AM真菌菌丝体网络是由AM真菌菌丝体在土壤生态系统中连接两株或两株以上植物根系所形成的菌丝体网络。随着菌根学研究的深入,如何直观的揭示AM真菌的生态学功能已经成为相关领域关注的热点问题。研究发现,利用同位素示踪技术可以开展AM真菌与宿主植物对土壤矿质营养的吸收、转运等方面的研究,以及菌丝体网络对不同宿主植物之间营养物质的分配研究和AM真菌在生态系统生态学中的功能研究。基于此,为了阐明同位素示踪技术在AM真菌研究中的价值,围绕菌根学最新研究进展,系统回顾了利用同位素示踪技术探究AM共生体对不同元素吸收和转运的机制、同位素示踪技术在AM真菌菌丝体网络研究中的价值和利用同位素示踪技术研究AM真菌在生态系统中的功能,为AM真菌生态学功能的研究提供理论基础,并对本领域未来的研究方向和应用前景进行展望。     

AM真菌在有机农业发展中的机遇

在农田生态系统中,许多农作物均为丛枝菌根(AM)真菌的优良宿主植物,当AM真菌与这些宿主植物建立共生关系之后,AM真菌的存在有益于宿主植物的生长。然而,传统农业耕作模式中化学肥料和农药的施用、耕作制度的不断调整和非宿主植物的种植等都不利于AM真菌的建植。有机农业生态系统排除了化学肥料和农药的施用,减少了对AM真菌生长不利的因素,促进了土壤中AM真菌数量的增加和群落多样性的提高。同时,AM真菌可以通过多种方式改善土壤物理结构、提高农作物对干旱胁迫的耐受能力以及宿主植物对病虫害的抗性/耐性、抑制杂草生长、促进营养物质的吸收,进而提高植物的生长和改善产品的品质。基于此,围绕AM真菌在有机农业发展中的生态学功能展开论述,分析当前有机农业生态系统存在的问题,探讨利用AM真菌发展有机农业的可行性及其发展的机遇,以期促进AM真菌在有机农业发展中的应用。     

Arbuscular mycorrhizal fungi might alleviate aluminium toxicity in banana plants

Under defined laboratory conditions it was shown that two glucosinolate-containing plant species, Tropaeolum majus and Carica papaya , were colonized by arbuscular mycorrhizal (AM) fungi, whereas it was not possible to detect AM fungal structures in other glucosinolate-containing plants (including several Brassicaceae). Benzylglucosinolate was present in all of the T. majus cultivars and in C. papaya it was the major glucosinolate. 2-Phenylethylglucosinolate was found in most of the non-host plants tested. Its absence in the AM host plants indicates a possible role for the isothiocyanate produced from its myrosinase-catalysed hydrolysis as a general AM inhibitory factor in non-host plants. The results suggest that some of the indole glucosinolates might also be involved in preventing AM formation in some of the species. In all plants tested, both AM hosts and non-hosts, the glucosinolate pattern was altered after inoculation with one of three different AM fungi ( Glomus mosseae , Glomus intraradices and Gigaspora rosea ), indicating signals between AM fungi and plants even before root colonization. The glucosinolate induction was not specifically dependent on the AM fungus. A time-course study in T. majus showed that glucosinolate induction was present during all stages of mycorrhizal colonization.     

Root apical meristems ofAllium porrum L. as affected by arbuscular mycorrhizae and phosphorus

Summary Arbuscular mycorrhizal (AM) fungi significantly improve plant growth in soils with low phosphorus availability and cause many changes in root morphology, similar to those produced by increased P nutrition, mainly depending on root apex size and activity. The aim of this work was to discriminate between the morphogenetic role of AM fungi and P in leek (Allium porrum L.) by feeding mycorrhizal and nonmycorrhizal plants with two nutrient solutions containing 3.2 or 96 M P and examining specific parameters related to adventitious root apices (apex size, mitotic cycle, and RNA synthesis). The results showed that AM fungi blocked meristem activity as indicated by the higher percentages of inactive apices and metaphases in the apical meristem of mycorrhizal plants, whereas the high P supply lengthened the mitotic cycle without blocking the apices, resulting in steady, slow root growth. The possible involvement of abscisic acid in the regulation of root apex activity is discussed.Abbreviations ABA abscisic acid - AM arbuscular mycorrhizae - CI and CII nonmycorrhizal control plants grown with low or high phosphorus concentration - MI and MII mycorrhizal plants grown with low or high phosphorus concentration - PGR plant growth regulator     

Field response of wheat to arbuscular mycorrhizal fungi and drought stress

Mycorrhizal plants often have greater tolerance to drought than nonmycorrhizal plants. This study was conducted to determine the effects of arbuscular mycorrhizal (AM) fungi inoculation on growth, grain yield and mineral acquisition of two winter wheat (Triticum aestivum L.) cultivars grown in the field under well-watered and water-stressed conditions. Wheat seeds were planted in furrows after treatment with or without the AM fungi Glomus mosseae or G. etunicatum. Roots were sampled at four growth stages (leaf, tillering, heading and grain-filling) to quantify AM fungi. There was negligible AM fungi colonization during winter months following seeding (leaf sampling in February), when soil temperature was low. During the spring, AM fungi colonization increased gradually. Mycorrhizal colonization was higher in well-watered plants colonized with AM fungi isolates than water-stressed plants. Plants inoculated with G. etunicatum generally had higher colonization than plants colonized with G. mosseae under both soil moisture conditions. Biomass and grain yields were higher in mycorrhizal than nonmycorrhizal plots irrespective of soil moisture, and G. etunicatum inoculated plants generally had higher biomass and grain yields than those colonized by G. mosseae under either soil moisture condition. The mycorrhizal plants had higher shoot P and Fe concentrations than nonmycorrhizal plants at all samplings regardless of soil moisture conditions. The improved growth, yield and nutrient uptake in wheat plants reported here demonstrate the potential of mycorrhizal inoculation to reduce the effects of drought stress on wheat grown under field conditions in semiarid areas of the world.     

Meeting a non-host: the behaviour of AM fungi

 Arbuscular mycorrhizal (AM) fungi are obligately biotrophic organisms that live symbiotically with the roots of most plants. The establishment of a functional symbiosis between AM fungi and host plants involves a sequence of recognition events leading to the morphological and physiological integration of the two symbionts. The developmental switches in the fungi are triggered by host signals which induce changes in gene expression and a process leading to unequivocal recognition between the two partners of the symbiosis. It has been calculated that about 80% of plant families from all phyla of land plants are hosts of AM fungi. The remaining plant species are either non-mycorrhizal or hosts of mycorrhizas other than the arbuscular type. Non-host plants have been used to obtain information on the factors regulating the development of a functional symbiosis. The aim of this present review is to highlight present-day knowledge of the fungal developmental switches involved in the process of host/non-host discrimination. The following stages of the life cycle of AM fungi are analysed in detail: spore germination, presymbiotic mycelial growth, differential branching pattern and chemotropism, appressorium formation, root colonization. Accepted: 17 June 1998     

Effects of arbuscular mycorrhiza and phosphorus application on artemisinin concentration in <Emphasis Type="Italic">Artemisia annua</Emphasis> L.

Annual wormwood (Artemisia annua L.) produces an array of complex terpenoids including artemisinin, a compound of current interest in the treatment of drug-resistant malaria. However, this promising antimalarial compound remains expensive and is hardly available on the global scale. Synthesis of artemisinin has not been proved to be feasible commercially. Therefore, increase in yield of naturally occurring artemisinin is an important area of investigation. The effects of inoculation by two arbuscular mycorrhizal (AM) fungi, Glomus macrocarpum and Glomus fasciculatum, either alone or supplemented with P-fertilizer, on artemisinin concentration in A. annua were studied. The concentration of artemisinin was determined by reverse-phase high-performance liquid chromatography with UV detection. The two fungi significantly increased concentration of artemisinin in the herb. Although there was significant increase in concentration of artemisinin in nonmycorrhizal P-fertilized plants as compared to control, the extent of the increase was less compared to mycorrhizal plants grown with or without P-fertilization. This suggests that the increase in artemisinin concentration may not be entirely attributed to enhanced P-nutrition and improved growth. A strong positive linear correlation was observed between glandular trichome density on leaves and artemisinin concentration. Mycorrhizal plants possessed higher foliar glandular trichome (site for artemisinin biosynthesis and sequestration) density compared to nonmycorrhizal plants. Glandular trichome density was not influenced by P-fertilizer application. The study suggests a potential role of AM fungi in improving the concentration of artemisinin in A. annua.     

Monitoring the decline in AM fungus populations and efficacy during a long term bare fallow

Producing nonmycorrhizal plants in the field is a challenge due to the ubiquitous distribution of arbuscular mycorrhizal [AM] fungi and impacts of chemical treatments upon nontarget organisms. A field plot was covered with ground cover fabric to prohibit plant growth and take advantage of the obligate symbiotic nature of AM fungi to selectively starve and remove them from the soil microbiological community. The decline in the AM fungus population was monitored through spore counts and most probable number bioassays. Response to inoculation experiments were conducted to contrast the response of Allium porrum L. to inoculation with in vitro produced spores of Glomus intraradices Schenck and Smith when plants were grown in the AM fungus-depleted soil vs. soil from an adjacent, cropped plot. Data indicated a strongly diminished, yet still viable population of AM fungi after 39 months of bare fallow. Plants grown in cropped soil showed no growth response nor increase in percentage root length colonized as a result of inoculation, while the response to inoculation of plants grown in the covered soil increased as the population of AM fungi declined below 1 propagule cm^?3.     

Systemic inhibition of arbuscular mycorrhiza development by root exudates of cucumber plants colonized by<Emphasis Type="Italic"> Glomus mosseae</Emphasis>

The arbuscular mycorrhizal (AM) non-host plants mustard, sugar beet, lupin and the AM host plant cucumber were used as test plants. Cucumber plants were grown either in the absence of the AM fungus (AMF) Glomus mosseae or in a split-root system, with one side mycorrhizal and one side non-mycorrhizal. Root exudates of the AM non-host plants, the non-mycorrhizal cucumber plants and the mycorrhizal and the non-mycorrhizal side of the split-root system of mycorrhizal cucumber plants were collected and applied to cucumber plants inoculated with the AMF. Root exudates of non-mycorrhizal cucumber plants showed a significant stimulatory effect on root colonization, whereas root exudates from the mycorrhizal and the non-mycorrhizal sides of a split-root system of a mycorrhizal cucumber plant did not show this stimulatory effect and were even slightly inhibitory. Root exudates of the two AM non-host plants mustard and sugar beet significantly reduced root colonization in cucumber plants, whereas no such effect was observed when root exudates of the AM non-host plant lupin were applied.     

AM真菌在植物病虫害生物防治中的作用机制

丛枝菌根(Arbuscular Mycorrhizae,AM)真菌是一类广泛分布于土壤生态系统中的有益微生物,能与大约80%的陆生高等植物形成共生体。由土传病原物侵染引起的土传病害被植物病理学界认定为最难防治的病害之一。研究表明,AM真菌能够拮抗由真菌、线虫、细菌等病原体引起的土传性植物病害,诱导宿主植物增强对病虫害的耐/抗病性。当前,利用AM真菌开展病虫害的生物防治已经引起生态学家和植物病理学家的广泛关注。基于此,围绕AM真菌在植物病虫害生物防治中的最新研究进展,从AM真菌改变植物根系形态结构、调节次生代谢产物的合成、改善植物根际微环境、与病原微生物直接竞争入侵位点和营养分配、诱导植株体内抗病防御体系的形成等角度,探究AM真菌在植物病虫害防治中的作用机理,以期为利用AM真菌开展植物病虫害的生物防治提供理论依据,并对本领域未来的发展方向和应用前景进行展望。     

Fungal root colonization responses in natural grasslands after long-term exposure to elevated atmospheric CO2

Arbuscular mycorrhizae, ubiquitous mutualistic symbioses between plant roots and fungi in the order Glomales, are believed to be important controllers of plant responses to global change, in particular to elevated atmospheric CO₂. In order to test if any effects on the symbiosis can persist after long-term treatment, we examined root colonization by arbuscular mycorrhizal (AM) and other fungi of several plant species from two grassland communities after continuous exposure to elevated atmospheric CO₂ for six growing seasons in the field. For plant species from both a sandstone and a serpentine annual grassland there was evidence for changes in fungal root colonization, with changes occurring as a function of plant host species. We documented decreases in percentage nonmycorrhizal fungal root colonization in elevated CO₂ for several plant species. Total AM root colonization (%) only increased significantly for one out of the five plant species in each grassland. However, when dividing AM fungal hyphae into two groups of hyphae (fine endophyte and coarse endophyte), we could document significant responses of AM fungi that were hidden when only total percentage colonization was measured. We also documented changes in elevated CO₂ in the percentage of root colonized by both AM hyphal types simultaneously. Our results demonstrate that changes in fungal root colonization can occur after long-term CO₂ enrichment, and that the level of resolution of the study of AM fungal responses may have to be increased to uncover significant changes to the CO₂ treatment. This study is also one of the first to document compositional changes in the AM fungi colonizing roots of plants grown in elevated CO₂. Although it is difficult to relate the structural data directly to functional changes, possible implications of the observed changes for plant communities are discussed.