七叶一枝花根的显微结构及其内生真菌分布研究

本文采用石蜡永久制片和光学显微摄像的方法对七叶一枝花Parispolyphylla根的显微结构及其内生真菌的分布进行了研究。结果表明,七叶一枝花的根茎由栓皮层、薄壁组织及维管组织组成,其中栓皮层由4层细胞组成;薄壁组织的细胞含有丰富的营养物质,其内有时分布有针状结晶束。不定根由表皮层、皮层、内皮层及维管束构成,表皮上有根毛,皮层所占根径的比例达80%以上;木质部为三原型。在七叶一枝花的根茎和不定根的皮层细胞中均有内生真菌的分布。真菌由表皮、外皮层侵入到皮层薄壁组织,在皮层薄壁细胞中形成菌丝结,并扩展成一定的侵染区域,部分皮层细胞中菌丝结已被消化吸收。内生真菌只侵染皮层薄壁细胞,不侵染维管柱。七叶一枝花可以通过消化细胞内的菌丝作为营养的来源之一。     

金银花根系VAM真菌侵染过程观察

在金银花生长季节,从西北农林科技大学北校区药用植物园采集金银花根系及根际土壤,采用形态学方法观察研究了VAM真菌侵染其根系的过程,并对其孢子进行了初步的形态学分类。结果表明:(1)VAM真菌侵染金银花根系时,先形成附着胞,然后入侵到皮层细胞,在根内形成线性菌丝、圈状菌丝;菌丝末端产生泡囊;在较粗的菌丝上产生丛枝状菌丝,而且VAM胞内菌丝主干可以穿越相邻的2个皮层细胞,在皮层中连续形成丛枝;VAM菌丝形成丛枝时,首先是胞内菌丝上膨大产生乳状突起,而后在乳状突起上产生较粗的丛枝柄,最后在这些丛枝柄上产生极细的丛枝状菌丝形成成熟的丛枝结构。(2)VAM真菌菌丝在金银花皮层细胞中,有伸展状态、菌丝圈及丛枝状态,所以金银花与VAM真菌形成的菌根是混合型菌根。(3)金银花根际土壤中至少存在3种类型的VAM真菌孢子,因此认为金银花至少可与3种VAM真菌共生。(4)金银花种植地土壤有效磷含量(6.6mg/kg)显著高于对照空地土壤有效磷含量(3.5mg/kg);金银花生长旺盛季(4月下旬到5月中旬)VAM真菌对其根系的侵染率高达81%。     

三种白及属植物不同生长发育时期的菌根显微结构

采用石蜡切片技术对白及Bletilla striata、黄花白及B. ochracea和小白及B. formosana的栽培种在生长期、花期、果期和休眠期的菌根解剖结构特征、菌根真菌入侵方式和菌丝特征等进行观察研究,以进一步了解菌根真菌与白及属植物的共生关系。结果表明,3种白及属植物的菌根真菌均是通过通道细胞侵入根皮层薄壁细胞,侵入后菌丝靠近皮层细胞的细胞核分布,最终在皮层细胞形成菌丝团;真菌侵染率和菌丝形态随着植物生长发育变化而变化,3种白及属植物均表现为花期和生长期的真菌侵染率较高,以丝状菌丝团为主,而果期和休眠期较低,以团块状菌丝团居多;同一时期不同植物类型的菌根特征无显著差异。     

山珊瑚内生菌根的研究

山珊瑚内生菌根真菌在人工培养基上分离培养不能生长。侵染菌丝由山珊瑚侧根表皮侵入,在皮层中部形成侵染通道。进入皮层细胞后形成丛枝吸器。被侵染的寄主细胞仍是生活细胞,但细胞质变稀,蛋白质、RNA含量很少。近中柱的6至8层皮层细胞壁增厚并木质化。丛枝吸器含有丰富的红淀粉,少量的中性脂肪、碱性蛋白质和D NA。菌丝丛枝干幼龄期电子致密,周围有界面物质包围,在衰老时泡囊化,界面物质亦瓦解。吸器由五边形结构组成。寄主细胞在被侵染前含淀粉质体、线粒体、高尔基体、内质网和核糖体,在被侵染后,淀粉质体消失,其它细胞器数量明显减少,而主要是微丝和小液泡及多泡体。文章讨论了山珊瑚菌根与天麻和泡囊-丛枝菌根的异同。     

人工栽培铁皮石斛菌根的细胞学研究

从细胞学水平上研究了人工栽培铁皮石斛的菌根特征。结果表明:真菌与铁皮石斛根成功地形成了菌根,真菌菌丝穿透根被细胞,并在根被的某个细胞中定殖,然后经由外皮层的通道细胞进入皮层薄壁细胞;皮层薄壁细胞层正是真菌与植物体相互作用的活跃部位;真菌侵染大多数的皮层薄壁细胞,并不能侵染内皮层及中柱细胞,从而使根仍然保持生活力。     

5种虾脊兰菌根显微结构观察

采用石蜡切片法观察5种虾脊兰菌根的显微结构、菌根真菌的侵入途径与分布特征,为更好地保护和开发利用虾脊兰属植物资源提供理论依据。结果表明:(1)5种虾脊兰菌根的显微结构由根被、皮层和中柱组成,根被细胞3～6层,皮层由9～13层薄壁细胞组成,韧皮部与木质部8～12束,呈辐射状相间排列,中柱中央为薄壁细胞组成的髓。(2)菌丝通过外皮层中的通道细胞侵入皮层,且皮层是内生菌根真菌寄居的主要区域,菌丝和菌丝结在靠近外皮层的几层皮层细胞中数量居多,菌丝在细胞核附近被消解,细胞核变形膨大。研究认为,5种虾脊兰可能拥有广泛的侵染能力较强的菌根真菌类型,使得这5种虾脊兰均具有较强的生态适应性。     

AM真菌与非菌根植物的相互作用关系

丛枝菌根(AM)真菌作为一类在全球分布广泛的土壤微生物,能够与陆地上大多数的维管植物形成专性共生关系,对于植物营养吸收和生态系统功能具有重要作用.而较少量的维管植物如苋科、黎科、石竹科、十字花科等植物被认为是非菌根植物.目前,对于这些非菌根植物与AM真菌之间的相互作用关系研究少且分散,缺乏系统总结.本文综述了非菌根植物的类型以及低侵染的原因,邻体植物形成的菌丝网络对AM真菌侵染非菌根植物的影响,并探讨AM真菌和非菌根植物之间可能存在的相互作用,以及植物-AM真菌之间的物质交换及可能存在的生态功能,旨在为进一步发挥非菌根植物在脆弱生态系统的功能潜力提供新思路.     

丛枝菌根真菌与转移Ri T一DNA胡萝卜根器官双重培养的形态学研究

利用双重培养技术,使丛枝菌根真菌GigasporamaFgarita侵染转移RiT-DNA胡萝卜根器官,建立共生联合体。菌丝对根器官的入侵、在根内的分布、原生质在菌丝内的双向流动、根外辅助细胞形成、菌丝的愈伤现象及孢子的产生、发育和再发芽的形态特征。所形成的形态构造对植物的养分吸收和运输有重要意义。     

密花石斛等六种兰科植物菌根的显微结构研究

本文对密花石斛等六种兰科植物根的显微结构进行了比较观察。结果表明,它们具有典型的兰科植物根,具根被和发达的皮层组织,皮层细胞内分布有针状结晶和菌根真菌形成的菌丝结,发现菌根真菌通过外皮层薄壁通道细胞或破坏根被组织和外皮层细胞侵入皮层细胞,形成内生菌根。     

银杏根际丛枝菌根真菌生长与根系黄酮含量的相关性研究

试验通过调查银杏根际丛枝菌根真菌的菌丝体长度、孢子密度及根系菌根侵染率,并测定银杏根系黄酮含量的季节性变化,研究二者的变化规律,分析相关关系。试验结果表明,年周期内银杏根际丛枝菌根真菌菌丝体长度、孢子密度与根系黄酮类化合物含量呈规律性变化:1月~3月根际丛枝菌根真菌菌丝长度有限,孢子密度、根系菌根侵染率与根系黄酮类化合物含量都最低;3月上中旬皆迅速增加,到9月达到全年最高峰;11月后,丛枝菌根真菌菌丝长度、孢子密度及根系菌根侵染率与根系黄酮类化合物含量均有所下降。通过数学模型分析,银杏根际丛枝菌根真菌菌丝长度、孢子密度及根系菌根侵染率与根系黄酮类化合物含量表现显著的正相关。     

Anatomy and mycotrophy of the achlorophyllous Afrothismia winkleri

Afrothismia winkleri develops fleshy rhizomes, densely covered with small root tubercles, narrowing to filiform roots with age. The exclusively intracellular mycorrhizal fungus has distinct morphologies in different tissues of the plant. In the filiform root the hyphae grow straight and vesicles are borne on short hyphal stalks. The straight hyphae are present in the epidermis of the root tubercles, but change to loosely coiled and swollen hyphae in the rhizome tissue. No penetration from epidermis to root cortex was found. From the rhizome, a separating cell layer permits only one or rarely two hyphal penetrations into the cortex of each root tubercle. The hyphae proceed apically within the root hypodermis in a spiral row of distinctively coiled hyphae, branches of which colonize the inner root cortex. In the inner root cortex the hyphal coils degenerate to amorphous clumps. In older roots the cortex itself also deteriorates, but epidermis, hypodermis, endodermis and central cylinder persist. The mycorrhizal pattern in A. winkleri is interpreted as an elaborate exploitation system whereby the fungus provides carbon and nutrients to the plant and, simultaneously but spatially distinct, its hyphae are used to translocate and store the matter within the plant. Several features indicate that the endophyte is an arbuscular mycorrhizal fungus.     

Colonisation patterns of root tissues byPhytophthora nicotianae var.parasitica related to reduced disease in mycorrhizal tomato

Tomato plants pre-colonised by the arbuscular mycorrhizal fungusGlomus mosseae showed decreased root damage by the pathogenPhytophthora nicotianae var.parasitica. In analyses of the cellular bases of their bioprotective effect, a prerequisite for cytological investigations of tissue interactions betweenG. mosseae andP. nicotianae v.parasitica was to discriminate between the hyphae of the two fungi within root tissues. We report the use of antibodies as useful tools, in the absence of an appropriate stain for distinguishing hyphae ofP. nicotianae v.parasitica from those ofG. mosseae inside roots, and present observations on the colonisation patterns by the pathogenic fungus alone or during interactions in mycorrhizal roots. Infection intensity of the pathogen, estimated using an immunoenzyme labelling technique on whole root fragments, was lower in mycorrhizal roots. Immunogold labelling ofP. nicotianae v.parasitica on cross-sections of infected tomato roots showed that inter or intracellular hyphae developed mainly in the cortex, and their presence induced necrosis of host cells, the wall and contents of which showed a strong autofluorescence in reaction to the pathogen. In dual fungal infections of tomato root systems, hyphae of the symbiont and the pathogen were in most cases in different root regions, but they could also be observed in the same root tissues. The number ofP. nicotianae v.parasitica hyphae growing in the root cortex was greatly reduced in mycorrhizal root systems, and in mycorrhizal tissues infected by the pathogen, arbuscule-containing cells surrounded by intercellularP. nicotianae v.parasitica hyphae did not necrose and only a weak autofluorescence was associated with the host cells. Results are discussed in relation to possible processes involved in the phenomenon of bioprotection in arbuscular mycorrhizal plants.     

Transmembrane electric potential difference of germ tubes of arbuscular mycorrhizal fungi responds to external stimuli

Measurements of the electric potential difference across the hyphal wall and the cell membrane were made on external hyphae of three species of arbuscular mycorrhizal fungus Gigaspora margarita , Scutellospora calospora and Glomus coronatum and on germ tubes of Gi. margarita . The values of transmembrane electric potential difference recorded (∼–40 mV) are less negative than those previously reported from hyphae of arbuscular mycorrhizal fungi closely associated with roots and from filamentous fungi. The external hyphae of arbuscular mycorrhizal fungi grown in soil had similar values of electric potential difference to those grown in soil-less culture, and to germ tubes. Thermodynamic calculations showed that despite these low values of electric potential difference, efficient high-affinity uptake of phosphate is possible. The transmembrane electric potential difference of germ tubes of Gi. margarita became more negative when plant root extract was added to the medium, showing for the first time that the early stages of interaction between plant and fungus occur via direct effects on the plasma membrane rather than via effects on gene expression. Addition of K⁺ reversibly depolarized the transmembrane electric potential difference of germ tubes of Gi. margarita , indicating that despite the low electric potential difference the fungus has control over the permeability of the plasmamembrane to K⁺.     

Mycorrhizal status and diversity of fungal endophytes in roots of common buckwheat (Fagopyrum esculentum) and tartary buckwheat (F. tataricum)

To determine the mycorrhizal status and to identify the fungi colonising the roots of the plants, common buckwheat (Fagopyrum esculentum) and tartary buckwheat (F. tataricum) were inoculated with an indigenous fungal mixture from a buckwheat field. Root colonisation was characterised by the hyphae and distinct microsclerotia of dark septate endophytes, with occasional arbuscules and vesicles of arbuscular mycorrhizal fungi. Sequences of arbuscular mycorrhizal fungi colonising tartary buckwheat clustered close to the Glomus species group A. Sequences with similarity to the Ceratobasidium/Rhizoctonia complex, a putative dark septate endophyte fungus, were amplified from the roots of both common and tartary buckwheat. To the best of our knowledge, this is the first report of arbuscular mycorrhizal colonisation in tartary buckwheat and the first molecular characterisation of these fungi that can colonise both of these economically important plant species.     

Pathways of Phosphorus Absorption and Early Signaling between the Mycorrhizal Fungi and Plants

This review highlights the key role that mycorrhizal fungi play in making phosphorus (Pi) more available to plants, including pathways of phosphorus absorption, phosphate transporters and plant-mycorrhizal fungus symbiosis, especially in conditions where the level of inorganic phosphorus (Pi) in the soil is low. Mycorrhizal fungi colonization involves a series of signaling where the plant root exudates strigolactones, while the mycorrhizal fungi release a mixture of chito-oligosaccharides and liposaccharides, that activate the symbiosis process through gene signaling pathways, and contact between the hyphae and the root. Once the symbiosis is established, the extraradical mycelium acts as an extension of the roots and increases the absorption of nutrients, particularly phosphorus by the phosphate transporters. Pi then moves along the hyphae to the plant root/fungus interface. The transfer of Pi occurs in the apoplectic space; in the case of arbuscular mycorrhizal fungi, Pi is discharged from the arbuscular to the plant’s root symplasm, in the membrane that surrounds the arbuscule. Pi is then absorbed through the plant periarbuscular membrane by plant phosphate transporters. Furthermore, plants can acquire Pi from soil as a direct absorption pathway. As a result of this review, several genes that codify for high-affinity Pi transporters were identified. In plants, the main family is Pht1 although it is possible to find others such as Pht2, Pht3, Pho1 and Pho2. As in plants, mycorrhizal fungi have genes belonging to the Pht1 subfamily. In arbuscular mycorrhizal fungi we found L1PT1, GiPT, MtPT1, MtPT2, MtPT4, HvPT8, ZmPht1, TaPTH1.2, GmosPT and LYCes. HcPT1, HcPT2 and BePT have been characterized in ectomycorrhizal fungi. Each gene has a different way of expressing itself. In this review, we present diagrams of the symbiotic relationship between mycorrhizal fungi and the plant. This knowledge allows us to design solutions to regional problems such as food production in soils with low levels of Pi.

     

Role of Arbuscular Mycorrhizal Fungi in Uptake of Phosphorus and Nitrogen From Soil

Abstract

Colonization of plant roots by arbuscular mycorrhizal fungi can greatly increase the plant uptake of phosphorus and nitrogen. The most prominent contribution of arbuscular mycorrhizal fungi to plant growth is due to uptake of nutrients by extraradical mycorrhizal hyphae. Quantification of hyphal nutrient uptake has become possible by the use of soil boxes with separated growing zones for roots and hyphae. Many (but not all) tested fungal isolates increased phosphorus and nitrogen uptake of the plant by absorbing phosphate, ammonium, and nitrate from soil. However, compared with the nutrient demand of the plant for growth, the contribution of arbuscular mycorrhizal fungi to plant phosphorus uptake is usually much larger than the contribution to plant nitrogen uptake. The utilization of soil nutrients may depend more on efficient uptake of phosphate, nitrate, and ammonium from the soil solution even at low supply concentrations than on mobilization processes in the hyphosphere. In contrast to ectomycorrhizal fungi, nonsoluble nutrient sources in soil are used only to a limited extent by hyphae of arbuscular mycorrhizal fungi. Side effects of mycorrhizal colonization on, for example, plant health or root activity may also influence plant nutrient uptake.     

Characterization of Mycorrhizas Formed by Glomus sp. on Roots of Hypernodulating Mutants of Lotus japonicus

Lotus japonicus hypernodulating mutants, Ljsym78-1 and Ljsym78-2, by the arbuscular mycorrhizal fungus Glomus sp. was characterized. The mutants are defective in systemic autoregulation of nodulation and nitrate inhibition, and form an excess of nodules and lateral roots. The percent root length colonized by the arbuscular mycorrhizal fungi was significantly higher for the mutant than wild-type roots. Detailed assessment of the colonization indicated that the percentage of colonization by arbuscules was increased, but that by external hyphae, internal hyphae and vesicles was decreased, in the mutant roots compared with the wild-type. The succinate dehydrogenase activity of arbuscules, external hyphae and internal hyphae showed similar trends. In addition, the majority of individual arbuscules that formed on the mutant roots had a well-developed and seemingly tough morphology. The results suggest that mutation at the Ljsym78 locus positively stimulates the growth and activity of arbuscules, but leads to reduced growth and activity of hyphae. We report the first identification of Lotus japonicus mutants that show significantly increased arbuscule formation and termed these mutants Arb⁺⁺. Received 8 August 2000/ Accepted in revised form 19 October 2000     

柑橘丛枝菌根形态结构观察

以田间栽培的‘国庆1号’温州蜜柑(Citrus unshiu ‘Guoqing No.1’)/枳(Poncirus trifoliata)和‘国庆4号’温州蜜柑(C.unshiu ‘Guoqing No.4’)/枳为试材观察丛枝菌根的形态结构。结果表明,泡囊、丛枝、侵入点、根内菌丝、根外菌丝、根外厚垣孢子等结构出现在柑橘根系中,说明柑橘属于典型的丛枝菌根植物。丛枝菌根结构中泡囊出现概率较小,丛枝随处可见,侵入点多样化。丛枝菌根的结构主要存在柑橘根段的伸长区和成熟区,首次观察到根冠和分生区也有侵染。     

Extraradical mycelium of the arbuscular mycorrhizal fungus Glomus lamellosum can take up,accumulate and translocate radiocaesium under root-organ culture conditions

Radiocaesium enters the food chain when plants absorb it from soil, in a process that is strongly dependent on soil properties and plant and microbial species. Among the microbial species, arbuscular mycorrhizal (AM) fungi are obligate symbionts that colonize the root cortex of many plants and develop an extraradical mycelial (ERM) network that ramifies in the soil. Despite the well-known involvement of this ERM network in mineral nutrition and uptake of some heavy metals, only limited data are available on its role in radiocaesium transport in plants. We used root-organ culture to demonstrate that the ERM of the AM fungus Glomus lamellosum can take up, possibly accumulate and unambiguously translocate radiocaesium from a 137Cs-labelled synthetic root-free compartment to a root compartment and within the roots. The accumulation of 137Cs by hyphae in the root-free compartment may be explained by sequestration in the hyphae or by a bottleneck effect resulting from a limited number of hyphae crossing the partition between the two compartments. Uptake and translocation resulted from the incorporation of 137Cs into the fungal hyphae, as no 137Cs was detected in mycorrhizal roots treated with formaldehyde. The importance of the translocation process was indicated by the correlation between 137Cs measured in the roots and the total hyphal length connecting the roots with the labelled compartment. 137Cs may be translocated via a tubular vacuolar system or by cytoplasmic streaming per se.