禾草内生真菌生物碱的研究进展

综述了国内外近20a以来在禾草内生真菌生物碱方面的研究进展。目前,已发现至少4大类10余种生物碱与内生真菌有关。各类生物碱中典型代表物的分子结构已完全清楚,部分内生真菌在离体条件下可产生除黑麦草碱外的生物碱,但产碱量较其在植物体中所产生的低很多,可相差150余倍之多。随着生物技术的发展,美国、新西兰等国在波胺、麦角碱和loline的生物合成途径方面已有了初步的进展,对个别具有重要功能基因以及其所编码的酶已有了深入研究。各种生物碱的致毒机理尚未完全清楚,除饱和吡咯化合物为新陈代谢类毒素和神经性毒素外,其余3类生物碱均为神经性毒素。生物碱可增加禾草对40余种害虫的抗性,并可增加对某些线虫和病害的抗性。诸多因素均可影响寄主植株中生物碱的种类和浓度,包括寄主植株：种群和生态型,植物品种和基因型,植株的部位和生长期;环境：气候因素,土壤养分,季节和年度变化;内生真菌菌株和草地管理利用方式等。用于生物碱检测的主要方法为预分离检测法和直接检测法,其中高效液相色谱法以其分离能力强、选择性高、测定灵敏度高,操作简单,可在室温下进行,应用范围极广的优点而广泛应用。目前,国际关于禾草内生真菌生物碱研究的重点包括创造不含对家畜有毒素的有益禾草-内生真菌共生体,开展基因工程研究以及合理利用生物碱,使其成为新一代的“生物农药”。     

禾草类内生真菌的研究进展*

感染内生真菌的禾草在牧草和草坪业上具有重要的生态和经济意义。关于禾草和内生真菌的互利共生作用已有大量报道,中就近年来有关禾草类内生真菌的起源和进化、内生真菌的生物和生态学作用以及内生真菌的应用前景方面的研究进展作一综述,以期更好地利用内生真菌造福人类。     

禾草内生真菌对其它微生物的影响研究进展

禾草内生真菌在宿主植物的茎叶等地上组织中普遍存在,不仅能够提高禾草对生物与非生物逆境的抗性,而且能够对周围环境中的不同微生物类群产生影响。主要总结了禾草Neotyphodium/Epichlo内生真菌对病原真菌、丛枝菌根真菌和土壤微生物的影响及其作用机理。发现禾草内生真菌普遍存在对病原真菌的抑制作用,而对丛枝菌根真菌存在不对称的竞争作用,且因种类而异。禾草内生真菌对土壤微生物群落的作用则会随着土壤类型和时间等外界因素发生变化。禾草内生真菌对不同类群微生物的影响机制主要包括:通过生态位竞争、抑菌物质分泌、诱导抗病性等对病原真菌造成影响;通过根系化学物质释放、营养元素调节、侵染条件差异等对丛枝菌根真菌造成影响;通过根际沉积物和凋落物等对土壤微生物群落造成影响。禾草内生真菌产生的生物碱能提高宿主植物对包括昆虫在内草食动物采食的抗性,影响病原菌的侵入、定殖和扩展;根组织分泌物中包含次生代谢产物能够抑制菌根真菌、土传病原真菌及其它土壤微生物的侵染与群落组成;也可能通过次生代谢物影响禾草的其它抗性。因此,禾草内生真菌在植物-微生物系统中的作用应该给予更多的关注和深入研究。     

禾草-内生真菌共生体在草地农业系统中的作用

综述了国内外近年对禾草 -内生真菌 (N eotyphodium)的研究进展。全世界现已报道 14种禾草内生真菌 ,与 2 3个属的禾草形成共生体 ,我国已在 13属 2 5种天然草地禾草中发现内生真菌 ,其中发草属 (Descampsia)、大麦属 (H ord eum)和赖草属(L eymus)以往在国际文献中未曾报道。内生真菌在禾草体内产生的生物碱 ,致使采食带菌禾草的马、牛、羊、鹿等家畜产生中毒症状 ,每年给美国、新西兰等国造成的经济损失达 6.4亿美元之多 ,对其毒理研究取得了进展。已发现我国醉马草 (Achnatheruminebrians)对家畜的毒性与内生真菌的侵染有关。内生真菌侵染增加可使禾草对 42种害虫的抗性 ,并可增加对某些线虫和病害的抗性。与不带菌禾草相比 ,带菌禾草的另一特点是抗逆性强 ,牧草产量高。国际在该领域的研究主要集中在多年生黑麦草(L olium p erenne)和高羊茅 (Festuca arundinacea)。我国的研究发现 ,带菌布顿大麦草 (H ordeum bodg anii)和圆柱披碱草(Elymus cylind ricus)的牧草产量分别增加 3 3 .3 %和 2 78.8% ,分孽数分别增加 13 6.8%和 84.5%。目前 ,国际研究的重点包括大规模开展内生真菌生物学与生态学特性的研究 ,创造不含对家畜有害毒素的有益禾草 -内生真菌共生体 ,培育带内生真菌的草坪草品种 ,培育抗毒     

不同pH对醉马草内生真菌共生体幼苗生长和产碱的影响

该研究考察了不同pH(3、5、7、9和11)处理对醉马草内生真菌共生体幼苗的形态指标、叶绿素、可溶性糖以及麦角酰胺和麦角新碱含量的影响,以明确共生体幼苗生长和产碱的最适pH条件。结果表明：（1）醉马草内生真菌共生体幼苗株高、根长、分蘖和生物量等均在pH 7时（达到最大）显著高于其他4个酸碱处理,而且4个生长指标在强碱性处理下均显著高于强酸处理。（2）幼苗叶绿素含量也在pH 7的中性条件下（达到最高）显著高于pH 3、pH 5和pH 11处理,且强碱性处理下叶绿素含量也显著高于强酸处理,但幼苗可溶性糖含量在不同pH处理之间没有显著变化。（3）在相同时间内,醉马草内生真菌共生体幼苗麦角酰胺和麦角新碱含量均随环境pH值升高而增加;在处理时间为15 d时,麦角酰胺在pH 9~11处理下积累量最多,麦角新碱含量在pH 11处理下达到最大值,酸性条件抑制醉马草内生真菌共生体幼苗产碱。研究发现,醉马草内生真菌共生体幼苗在中性环境条件下生长最佳,且在碱性条件下生长较酸性条件下生长良好,而体内麦角酰胺和麦角新碱的积累在强碱性条件下达到峰值,可将醉马草内生真菌共生体应用于盐碱地的栽培绿化。     

禾草内生真菌作为生防因子的潜力分析

早熟禾亚科多种禾草可与Neotyphodium内生真菌形成禾草-内生真菌共生体, 这种植物-微生物共生体性状较为稳定, 且在自然界中广泛存在。禾草-内生真菌共生体稳定的互利共生关系不但保证了内生真菌所需的全部营养物质, 而且共生体产生的次生代谢物又可显著提高宿主禾草对生物胁迫的抗逆性。众多研究表明, 内生真菌的侵染可显著提高宿主禾草对虫害、病害及伴生植物等多种生物胁迫的抗性。据不完全统计, 禾草内生真菌对蛛形纲、线虫纲、昆虫纲3个纲至少79个种的害虫表现出较明显的抗性, 对至少22个种的病原真菌表现出明显的抗性。尽管利用内生真菌进行禾草品种选育及其品质改良的技术日趋成熟, 但是内生真菌在不同宿主禾草之间高效的替代转化技术, 及其在宿主体内遗传的稳定性仍有待于进一步深入探索。研究者把禾草内生真菌作为生防手段, 在未来的应用过程中不应只考虑其与宿主禾草之间的共生特异性, 而应更全面地分析禾草-内生真菌-生态环境之间的相互关系, 让内生真菌更好地为人类服务。     

植物内生真菌防治根结线虫研究进展

根结线虫病是对农作物危害严重且难以防治的病害,并随着我国设施农业的发展日趋严重。常规的化学防治方法因毒性大、破坏生态环境而不适应农业的可持续发展。作为一种能稳定寄生在作物体内的生物防治真菌,内生真菌通过抑制卵的孵化、降低J2期线虫幼虫活力、抑制线虫的入侵、延缓雌虫发育、减少产卵数目、降低作物根中根结和卵块数量,来实现稳定、高效、安全地防治根结线虫病害。近年来,内生真菌的作用机制得到广泛关注和研究,取得了显著进展。本文综述近年来内生真菌生物防治根结线虫机制的研究进展,总结了内生真菌直接攻击、资源竞争、代谢物胁迫、防御激活等4种主要机制,探讨其存在的问题,以期为进一步开发、应用植物内生真菌进行生物防治提供帮助。     

光照强度和光周期对醉马草内生真菌共生体幼苗生长和生物碱积累的影响

该研究通过测定不同光周期(8、12、14和16h·d~(-1))和光照强度(1 500、2 500和3 500lux)处理下醉马草内生真菌共生体幼苗的形态指标以及叶绿素、可溶性糖、麦角酰胺和麦角新碱的含量,以明确醉马草内生真菌共生体幼苗生长和生物碱积累的最适光照条件,为醉马草内生真菌共生体的应用提供理论依据。结果发现:(1)醉马草内生真菌共生体幼苗株高、叶绿素和可溶性糖含量随着光照时间的延长而增加,并在光周期为16h·d~(-1)时显著(P0.05)高于其他处理;根长、单株分蘖数和单株生物量均先升高后降低,且均在14h·d~(-1)处理下达到最大值。(2)随着光照强度的增加,醉马草内生真菌共生体幼苗4个形态指标以及叶绿素和可溶性糖含量均呈增加的趋势,并在光照强度为3 500lux时均达到最大值。(3)随着处理时间的延长,醉马草内生真菌共生体幼苗麦角酰胺和麦角新碱的含量在不同光周期处理下均呈上升的趋势,并在光周期为12h·d~(-1)和光照强度为2 500lux处理下麦角酰胺和麦角新碱的含量均显著高于其他处理(P0.05),且在处理第15天时达到最大值。研究表明,适宜的光照环境能显著促进醉马草内生真菌共生体幼苗生长和生物碱的积累,并以12h·d~(-1)光周期和2 500lux光照处理下最有利于麦角酰胺和的麦角新碱积累。     

Advances in research of Achnatherum inebrians-Epichloë endophyte symbionts北大核心CSCD

Research on drunken horse grass (Achnatherum inebrians)-endophytic fungi (Epichloë gansuensis, E. inebrians) represented an important area of endophyte research in China. Compared with tall fescue (Festuca arundinacea)-endophyte (E. coenophiala) in the United States and perennial ryegrass (Lolium perenne)-endophyte (E. festucae var. lolii) in New Zealand, A. inebrians-endophyte research in China is becoming a leading branch of endophyte research. The studies of A. inebrians-endophyte symbionts over the past three decades were reviewed, mainly including endophyte distribution, detection methods, infection rate, fungal diversity, stress tolerances of drought, cold, salt, heavy metal, pest, disease and their mechanisms, secondary metabolite of alkaloids, feeding experiments and its ecological functions etc. Research reveals that drunken horse grass itself has no toxicity, the grazed animals will be intoxicated if the grass bears infection by Epichloë endophytes and produces ergot alkaloids. Future research will focus on E. gansuensis and E. inebrians genomics and endophyte functions. In other research we will create new grass cultivars that are 1) sanitized of the endophyte and non-toxic, 2) utilizing novel endophytes that deter birds feeding and 3) utilizing endophytes that are modified to produce novel fungicides, pesticides or medicines. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

Epichloë endophyte effects on leaf blotch pathogen (Rhynchosporium sp.) of tall fescue (Schedonorus phoenix) vary among grass origin and environmental conditions

ABSTRACT

Background

Systemic Epichloë endophytes are common fungal symbionts of many cool-season grasses. They are known for their capability of increasing host plant tolerance against biotic and abiotic stressors, including grass pathogens. However, results on endophyte-mediated disease resistance have been ambiguous, and the underlying mechanisms of disease resistance remain unknown.     

Identification and characterization of bacterial endophytes of rice

We isolated seven different bacteria from rice seedlings grown from surface sterilized seeds. Three were associated with the rice seed husk and the other four were growing endophytically within the seed. Microscopic studies revealed that the endophytes were concentrated in the root stele region. Some of the bacteria exhibited strong anti-fungal activity against Rhizoctonia solani, Pythium myriotylum, Guamannomyces graminis and Heterobasidium annosum.     

Exploitation of endophytes for sustainable agricultural intensification

Intensive agriculture, which depends on unsustainable levels of agrochemical inputs, is environmentally harmful, and the expansion of these practices to meet future needs is not economically feasible. Other options should be considered to meet the global food security challenge. The plant microbiome has been linked to improved plant productivity and, in this microreview, we consider the endosphere – a subdivision of the plant microbiome. We suggest a new definition of microbial endophyte status, the need for synergy between fungal and bacterial endophyte research efforts, as well as potential strategies for endophyte application to agricultural systems.     

ROOTS OF METAL HYPERACCUMULATING POPULATION OF THLASPI PRAECOX (BRASSICACEAE) HARBOUR ARBUSCULAR MYCORRHIZAL AND OTHER FUNGI UNDER EXPERIMENTAL CONDITIONS

Thlaspi praecox (Brassicaceae) is a recently discovered metal hyperaccumulating plant species colonized by arbuscular mycorrhizal fungi (AMF). The identity and diversity of the AMF colonizing its roots have not been determined so far. Therefore, T. praecox was inoculated with an indigenous fungal mixture from a metal polluted site and grown in original polluted soil/ commercial substrate mixtures (i.e., 100%, 50%, and 25%). Low to moderate mycorrhizal frequencies (F = 33–68%) and only rare arbuscules were observed. Densities of vesicles and microsclerotia, typical structures of dark septate endophytes (DSE), were greater in pots with 100% original polluted soil. In contrast, the highest diversity of fungal genotypes was observed in the roots from 25% polluted soil/ commercial substrate mixture, with the lowest soil concentrations of Cd, Zn, and Pb. The sequences obtained corresponded to Glomus species (Glomeromycota), to putative DSE Phialophora verrucosa and Rhizoctonia sp. and to some other fungi from Asco- and Basidiomycota, that are known to associate with plants, namely Capnobotryella sp., Penicillium brevicompactum, Rodotorula aurantiaca and Rodotorula slooffiae. This is the first report of DSE occurrence in roots of hyperaccumulating T. praecox, a promising candidate for phytoextraction.     

Fungal endophytes from Dioscorea zingiberensis rhizomes and their antibacterial activity

AIMS: The aim of the study was to isolate and characterize the endophytic fungi from the rhizomes of the Chinese traditional medicinal plant Dioscorea zingiberensis and to detect their antibacterial activities. METHODS AND RESULTS: After strict sterile sample preparation, nine fungal endophytes were isolated from rhizomes of the Chinese traditional medicinal plant D. zingiberensis. The endophytes were classified by morphological traits and internal transcribed spacer (ITS) rRNA gene sequence analysis. Their ITS rDNA sequences were 99-100% identical to Nectria, Fusarium, Rhizopycnis, Acremonium and Penicillium spp. respectively. Of these, the most frequent genera were Fusarium and Nectria. One isolate, Dzf7, was unclassified on the basis of its low sequence similarity. The next closest species was Alternaria longissima (c. 92.4% sequence similarity). Endophyte isolate Dzf5 showed the closest sequence similarity (c. 99.5%) to an uncultured soil fungus (DQ420800) obtained from Cedar Creek, USA. Bioassays using a modified broth dilution test were used to detect the antibacterial activity of n-butanol extracts of both mycelia and culture filtrates of D. zingiberensis showed biological activity against Bacillus subtilis, Staphylococcus haemolyticus, Escherichia coli and Xanthomonas vesicatoria. Minimal inhibitory concentration (MIC) values of the extracts were between 31 x 25 microg ml(-1) and 125 microg ml(-1). CONCLUSIONS: Endophytic fungus Dzf2 (c. 99 x 8% sequence similarity to Fusarium redolens) isolated from D. zingiberensis rhizome showed the most potent antibacterial activities. SIGNIFICANCE AND IMPACT OF THE STUDY: Endophytic fungi isolated from D. zingiberensis may be used as potential producers of antibacterial natural products.