植酸钠对菌根真菌根内菌丝碱性磷酸酶活性及根外菌丝生长的影响

采用三室隔网培养装置,以玉米为宿主植物,接种丛枝菌根真菌(AM)(Glomus intraradices),研究了不同用量的植酸钠对AM真菌生长和代谢活性的影响．研究发现,接种AM真菌的植株地上部和根系的P浓度和吸P量,比非菌根植物的提高了1～2倍．外源植酸钠的存在,显著降低了AM真菌根内菌丝的碱性磷酸酶活性,增加了AM真菌在土壤中的菌丝密度．结果表明,外源植酸钠对根内AM真菌碱性磷酸酶活性和真菌根外菌丝的生长具有调控(增减)作用,并且AM真菌提高了植物对土壤固有养分和外源植酸钠中P的吸收和利用．     

宿主植物栽培密度对AM真菌生长发育的影响

温室盆栽条件下宿主植物高粱(SorghumvulgarePers.)的栽培密度对丛枝菌根(Arbuscularmycorrhizae,AM)真菌Glomusmosseae(Nicol.&Gerd.)Gerdemann&Trappe生长发育的影响试验结果表明:60株/盆密度处理的根外菌丝量及孢子数均高于其它处理。在一定栽培密度下(20~60株/盆),植株根系可溶性糖浓度与根外菌丝量呈显著负相关,与菌根侵染率呈显著正相关。植株根中磷浓度与根外菌丝量、根外菌丝量与孢子数均呈显著正相关。植株根中磷浓度与菌根侵染率呈显著负相关。结果说明:适当密植虽对植株生长有一定影响,但却促进了真菌的生长,此时菌根共生体有可能由互惠共生开始向偏利共生或弱寄生转化。密植作为一种调控手段,在菌剂生产中能获得较大数量的侵染根段、菌丝及孢子等繁殖体。     

宿主植物栽培密度对AM真菌生长发育的影响*

温室盆栽条件下宿主植物高粱(SorghumvulgarePers.)的栽培密度对丛枝菌根(Arbuscularmycorrhizae,AM)真菌Glomusmosseae(Nicol.&Gerd.)Gerdemann&Trappe生长发育的影响试验结果表明:60株/盆密度处理的根外菌丝量及孢子数均高于其它处理。在一定栽培密度下(20~60株/盆),植株根系可溶性糖浓度与根外菌丝量呈显著负相关,与菌根侵染率呈显著正相关。植株根中磷浓度与根外菌丝量、根外菌丝量与孢子数均呈显著正相关。植株根中磷浓度与菌根侵染率呈显著负相关。结果说明:适当密植虽对植株生长有一定影响,但却促进了真菌的生长,此时菌根共生体有可能由互惠共生开始向偏利共生或弱寄生转化。密植作为一种调控手段,在菌剂生产中能获得较大数量的侵染根段、菌丝及孢子等繁殖体。     

外生菌根菌丝桥在板栗幼苗间传递磷的效应

采用^32P示踪和4室根箱方法研究了外生菌根菌丝桥对板栗磷营养和植株间磷素传递作用的效应。给一株板栗幼苗(供体)接种外生菌根真菌美味牛肝菌(Boletus edulis)、褐环乳牛肝菌(Suillus luteus),菌根真菌在侵染供体植物以后其根外菌丝继续生长并侵染邻近的另外一株板栗植株(受体)。同位素示踪试验表明,供体板栗体内的^32P可通过菌丝桥传递给受体板栗,受体植株不仅根中^32P放射性强度高于对照,而且茎中^32P强度也显著高于对照。说明外生菌根真菌在不同板栗植株间形成了菌丝桥,但是菌丝桥传递的磷的数量很有限,仅占供体植株体内总磷量的5％-8％。美味牛肝菌和褐环乳牛肝菌侵染供体板栗植株以后,使植株含磷量、总吸磷量和生物量较对照明显增加。受体板栗幼苗在菌丝桥建立以后其植株含磷量和总吸磷量显著高于对照,但生物量与对照没有显著差别。     

磷水平对接种丛枝菌根真菌甜玉米苗期生长的影响

研究了不同外源磷水平条件下,接种丛枝菌根真菌根内球囊霉(Glomus intraradices)对寄主植物甜玉米菌根侵染率、地上部和地下部鲜重、氮磷含量、精氨酸含量影响。结果表明:丛枝菌根真菌能够很好的侵染于玉米植株根系。且不同磷水平条件下,菌根侵染率差异较显著。在低磷水平下,菌根侵染率较高。孢子数量随着磷水平提高而增加。菌丝室根外菌丝鲜重在P40时最高。菌根化的甜玉米生物量及氮磷含量显著高于对照组。此外,低磷水平促使甜玉米地上部和地下部鲜重显著提高。甜玉米地上部总氮和地下部总氮含量分别在P40、P80和P20、P40时最高。地上部总磷和地下部总磷含量分别在P80和P160时最高。菌根精氨酸含量在低磷(P20)时最高。研究表明接种丛枝菌根真菌可促进甜玉米幼苗生长并与外源磷水平有关。     

不同丛枝菌根真菌侵染对土壤结构的影响

为了定量化比较研究接种丛枝菌根真菌后,根际、菌根际和菌丝际土壤结构的变化,采用四室分根装置,比较中性紫色土接种不同AM真菌后,菌根际、根际、菌丝际和非根际土壤平均重量直径(MWD)、几何平均直径(GMD)和大于0.25mm团聚体总量(R_0.25)的变化。结果表明:接种3个菌种后菌丝际EEG和有机质含量均呈高于菌根际的趋势。菌丝密度和易提取球囊霉素相关蛋白(EEG)与MWD、GMD和R_0.25呈显著正相关,菌根际和菌丝际土壤水稳性R_0.25与菌丝密度显著正相关,相关系数分别为0.777和0.671。接种G. mosseae的菌根际土壤R_0.25值显著高于其它分室土壤,而接种G.etunicatum的菌丝际土壤R_0.25值显著高于其它分室土壤。试验结果在一定程度上说明不同菌种对土壤结构均有不同程度的影响,反映了丛枝菌根真菌生态功能的多样性。     

接种根内球囊霉(Glomus intraradices)对地毯草(Axonopus compressus)再生及土壤的影响

研究主要探讨了根内球囊霉(Glomus intraradices)对地毯草(Axonopus compressus)再生以及土壤性状的影响。结果发现: (1)接种AMF(Arbuscular Mycorrhiza Fungi)能够显著提高地毯草的生物量、绝对再生高度和根系活力; (2)接种处理对地毯草地上部和地下部总N 含量的影响不显著, 但接种处理地毯草地上部总P 含量显著高于对照; (3)接种组的土壤pH 显著高于对照组, 且土壤团聚体的平均重量直径和几何均重直径较对照分别提高了39.1%和114.5%。可见,菌根真菌能够有效促进地毯草的生长, 并在一定程度上有利于土壤的理化性质的改良。     

珠状巨孢囊霉的单主寄生营养液培养及宿主根分泌物特性*

为研究丛枝菌根真菌对宿主植物根分泌物的影响,在营养液培养条件下成功地建立了菌根真菌Gigaspora margarita与转移Ri T-DNA胡萝卜根器官之间的无菌单主寄生培养方法。接种发芽的孢子四个月后,对根段染色观测,发现萌发孢子的菌丝能够入侵到根段的皮层细胞内,根细胞内有菌丝的折叠卷曲现象,并开始形成了新的孢子。利用高压液相色谱测定各处理营养液中根分泌物的成分,发现菌根分泌的苹果酸和乙酸含量高于对照处理,菌根营养液的pH升高幅度也大于未接种的对照根。     

覆膜与接种AM真菌对半干旱区玉米根际土壤理化性质的影响

本研究采用裂区试验设计,主区设置了3种覆膜方式:露地平播(即常规播种方法,无覆膜)、半覆膜平作(即常规播种方法,覆膜占小区面积一半)、全膜垄上穴播(即起垄后小区全覆膜,垄上播种),副区设置了2个丛枝菌根(AM)真菌接种水平:接种AM真菌(AM)和不接种对照(CK),研究了大田条件3种覆膜方式下接种AM真菌对半干旱区春播玉米根际土壤养分、有机碳含量及AM真菌特性(侵染率、根外菌丝密度与土壤球囊霉素)的影响。结果表明:3种覆膜方式下,与不接种对照相比,接种AM真菌显著提高了根系侵染率、根外菌丝密度、土壤中球囊霉素和有机碳含量、植株干重、碳氮比和土壤含水量,同时显著促进了土壤养分吸收(个别例外),其中土壤根外菌丝密度、易提取球囊霉素、有机碳、速效磷和速效钾含量、碳氮比随着覆膜方式由无覆膜-半覆膜-全覆膜的变化呈降低趋势,而植株干重、土壤中总球囊霉素、全氮和含水量随着覆膜方式由无覆膜-半覆膜-全覆膜的变化呈升高的趋势。全覆膜结合接种AM真菌在促进西北半干旱地区田间作物生长、提高土壤含水量、以及改善菌根侵染率、菌丝密度与土壤中球囊霉素含量的作用最大,但降低了土壤养分,后期还可能需要通过合理施肥措施加以维持土壤肥力水平。相关分析表明,土壤根外菌丝密度和球囊霉素含量与土壤矿质养分和水分存在一定程度的协同效应,接种AM真菌有助于根际土壤养分转化,促进植物生长。     

丛枝菌根真菌对豆科作物生长和生物固氮及磷素吸收的影响

本研究以大豆为材料,采用盆栽和田间试验,探讨丛枝菌根真菌(AMF)对豆科作物生长的影响。盆栽试验设置了接种(+AMF)和不接种(-AMF)丛枝菌根真菌处理,田间试验设置了AMF菌丝非限制与限制处理。盆栽试验结果表明: 接种AMF显著提高了大豆地上部生物量(16.5%)和大豆根瘤数(131.4%),地上部磷含量、磷吸收量、氮含量和氮吸收量也显著增加。田间试验中,AMF菌丝非限制处理下大豆的地上部生物量、根系生物量、根瘤数量分别比限制处理下显著提高了123.6%、61.5%和212.5%,地上部和根系磷吸收量、氮含量、氮吸收量均显著高于限制处理,大豆根际土壤速效氮和有效磷含量也均显著高于限制处理。本研究可为进一步认识豆科作物与AMF的共生关系及田间磷肥高效利用提供理论参考。     

Litter N retention over winter for a low and a high phenolic species in the alpine tundra

Mycorrhizal fungus colonization of roots may modify plant metal acquisition and tolerance. In the present study, the contribution of the extraradical mycelium of an arbuscular mycorrhizal (AM) fungus, Glomus mosseae (BEG 107), to the uptake of metal cations (Cu, Zn, Cd and Ni) by cucumber (Cucumis sativus) plants was determined. The influence of the amount of P supplied to the hyphae on the acquisition and partitioning of metal cations in the mycorrhizal plants was also investigated. Pots with three compartments were used to separate root and root-free hyphal growing zones. The shoot concentration of Cd and Ni was decreased in mycorrhizal plants compared to non-mycorrhizal plants. In contrast, shoot Zn and Cu concentrations were increased in mycorrhizal plants. High P supply to hyphae resulted in decreased root Cu concentrations and shoot Cd and Ni concentrations in mycorrhizal plants. These results confirm that some elements required for plant growth (P, Zn, Cu) are taken up by mycorrhizal hyphae and are then transported to the plants. Conversely, Cd and Ni were transported in much smaller amounts by hyphae to the plant, so that arbuscular mycorrhizal fungus colonization could partly protect plants from toxic effects of these elements. Selective uptake and transport of plant essential elements over non-essential elements by AM hyphae, increased growth of mycorrhizal plants, and metal accumulation in the root may all contribute to the successful growth of mycorrhizal plants on metal-rich substrates. These effects are stimulated when hyphae can access sufficient P in soil.     

Response of the grapevine rootstock Richter 110 to inoculation with native and selected arbuscular mycorrhizal fungi and growth performance in a replant vineyard

Two indigenous arbuscular mycorrhizal (AM) fungi from the Mediterranean wine growing area in the Northeast of Spain were isolated and classified as Glomus intraradices Schenck & Smith. Both native fungi were found to increase the growth of the vine rootstock 110 Richter under greenhouse conditions compared with G. intraradices (BEG 72) and a phosphorus (P) fertilization treatment. The effectivity of field inoculation of Cabernet Sauvignon plants grafted on Richter 110 with the former native fungi and with G. intraradices BEG 72 in a replant vineyard severely infested by the root-rot fungus Armillaria mellea (Vahl ex Fr.) Kummer was assessed. The native fungi were not effective at enhancing plant development, and only G. intraradices BEG 72, resulted in a positive response. Field inoculation with this selected fungus increased plant shoot dry weight at the end of the first growing season.     

Application of in vitro methods to study carbon uptake and transport by AM fungi

Just as multi-compartmented root chambers have advantages over standard plastic pots for the study of nutrient uptake by arbuscular mycorrhizal [AM] fungi in soil, so the split-plate in vitro system has advantages over the standard dual culture system for the study of the physiology of AM fungi. We used the split-plate culture system of Ri T-DNA transformed Daucus carota L. roots and Glomus intraradices Schenck & Smith, in which only the fungus has access to the distal compartment, to study the ability of germ tubes and extraradical and intraradical hyphae to take up ¹³C-labeled substrates. Labeled substrates were added to one side of the plate divider and plates were incubated for 8 weeks while the fungus proliferated on the side from which the root was excluded. Tissues then were recovered from the plate and examined via NMR spectroscopy. Results showed that the morphological phases of the fungus differed in their ability to take up these substrates, most notably that intraradical hyphae take up hexose while extraradical hyphae cannot. In addition, NMR studies indicated that intraradical hyphae actively synthesized lipids while extraradical hyphae did not. These data show that eventual axenic culture of AM fungi is more than a matter of finding the proper substrate for growth. Genetic regulation must be overcome to make extraradical hyphae behave like intraradical hyphae in terms of C uptake and metabolism. This revised version was published online in June 2006 with corrections to the Cover Date.     

The response of Glomus fistulosum–maize mycorrhiza to treatments with culture fractions from Pseudomonas putida

 This study examined which culture fraction of the plant-growth-promoting bacterium Pseudomonas putida (Trevisan) Migula has an effect on growth and mycorrhiza formation of maize (Zea mays L.). Shoot dry weight and total leaf area of plants did not increase after inoculation with Glomus fistulosum but were significantly higher than the controls when the plants were dualinoculated with G. fistulosum and living cells of P. putida. Mycorrhizal infection of the roots was significantly higher when plants were inoculated with G. fistulosum together with living cells of P. putida or with G. fistulosum and dialysed cell extracts of P. putida than with G. fistulosum alone. Development of arbuscular mycorrhizal (AM) extraradical hyphae and the proportion of extraradical hyphae showing NADH diaphorase activity were significantly enhanced by inoculation of plants with living cells of P. putida or dialysed cell extracts of P. putida. No stimulation of extraradical hyphae proliferation from in vitro incubated mycorrhizal root segments was observed after application of culture fractions of P. putida. However, the percentage contamination of the root segments by extraneous filamentous fungi significantly decreased in the presence of livingcells of P. putida. Accepted: 12 January 1996     

Interactions between biochar and mycorrhizal fungi in a water-stressed agricultural soil

Biochar may alleviate plant water stress in association with arbuscular mycorrhizal (AM) fungi but research has not been conclusive. Therefore, a glasshouse experiment was conducted to understand how interactions between AM fungi and plants respond to biochar application under water-stressed conditions. A twin chamber pot system was used to determine whether a woody biochar increased root colonisation by a natural AM fungal population in a pasture soil (‘field’ chamber) and whether this was associated with increased growth of extraradical AM fungal hyphae detected by plants growing in an adjacent (‘bait’) chamber containing irradiated soil. The two chambers were separated by a mesh that excluded roots. Subterranean clover was grown with and without water stress and harvested after 35, 49 and 63 days from each chamber. When biochar was applied to the field chamber under water-stressed conditions, shoot mass increased in parallel with mycorrhizal colonisation, extraradical hyphal length and shoot phosphorus concentration. AM fungal colonisation of roots in the bait chamber indicated an increase in extraradical mycorrhizal hyphae in the field chamber. Biochar had little effect on AM fungi or plant growth under well-watered conditions. The biochar-induced increase in mycorrhizal colonisation was associated with increased growth of extraradical AM fungal hyphae in the pasture soil under water-stressed conditions.     

Expressed genes in the extraradical hyphae of an arbuscular mycorrhizal fungus, Glomus intraradices, in the symbiotic phase

To collect extraradical hyphae of arbuscular mycorrhizal (AM) fungi for RNA isolation, a PVDF membrane was laid on the hyphal compartment of a two-compartment culture system of transformed carrot hairy roots and Glomus intraradices. Extraradical hyphae free from host tissue were easily collected, and their RNA was rapidly extracted with a modified acid guanidinium thiocyanate-phenol-chloroform method. A 3'-RACE (rapid amplification of cDNA ends) of a known gene indicated that this protocol enabled the isolation of mRNA molecules as small as 2.3 kb. The cDNA libraries of an AM fungus from the aseptic extraradical hyphae in a symbiotic state were constructed for the first time. Three-fourth of 150 ESTs (expressed sequence tags) indicated low or no similarities to known sequences from other organisms.     

Hyphosphere interactions between Rhizophagus irregularis and Rahnella aquatilis promote carbon–phosphorus exchange at the peri-arbuscular space in Medicago truncatula

Arbuscular mycorrhizal (AM) fungi form a continuum between roots and soil. One end of this continuum is comprised of the highly intimate plant–fungus interface with intracellular organelles for nutrient exchange, while on the other end the fungus interacts with bacteria to compensate for the AM fungus' inability to take up organic nutrients from soil. How both interfaces communicate in this highly complex tripartite mutualism is widely unknown. Here, the effects of phosphate-solubilizing bacteria (PSB) Rahnella aquatilis dwelling at the surface of the extraradical hyphae of Rhizophagus irregularis was analysed based on the expression of genes involved in C-P exchange at the peri-arbuscular space (PAS) in Medicago truncatula. The interaction between AM fungus and PSB resulted in an increase in uptake and transport of Pi along the extraradical hyphae and its transfer from AM fungus to plant. In return, this was remunerated by a transfer of C from plant to AM fungus, improving the C-P exchange at the PAS. These results demonstrated that a microorganism (i.e., a PSB) developing at the hyphosphere interface can affect the C-P exchange at the PAS between plant and AM fungus, suggesting a fine-tuned communication operated between three organisms via two distantly connected interfaces.     

Translocation and Utilization of Fungal Storage Lipid in the Arbuscular Mycorrhizal Symbiosis

The arbuscular mycorrhizal (AM) symbiosis is responsible for huge fluxes of photosynthetically fixed carbon from plants to the soil. Carbon is transferred from the plant to the fungus as hexose, but the main form of carbon stored by the mycobiont at all stages of its life cycle is triacylglycerol. Previous isotopic labeling experiments showed that the fungus exports this storage lipid from the intraradical mycelium (IRM) to the extraradical mycelium (ERM). Here, in vivo multiphoton microscopy was used to observe the movement of lipid bodies through the fungal colony and to determine their sizes, distribution, and velocities. The distribution of lipid bodies along fungal hyphae suggests that they are progressively consumed as they move toward growing tips. We report the isolation and measurements of expression of an AM fungal expressed sequence tag that encodes a putative acyl-coenzyme A dehydrogenase; its deduced amino acid sequence suggests that it may function in the anabolic flux of carbon from lipid to carbohydrate. Time-lapse image sequences show lipid bodies moving in both directions along hyphae and nuclear magnetic resonance analysis of labeling patterns after supplying 13C-labeled glycerol to either extraradical hyphae or colonized roots shows that there is indeed significant bidirectional translocation between IRM and ERM. We conclude that large amounts of lipid are translocated within the AM fungal colony and that, whereas net movement is from the IRM to the ERM, there is also substantial recirculation throughout the fungus.     

Branched absorbing structures (BAS): a feature of the extraradical mycelium of symbiotic arbuscular mycorrhizal fungi

The present work describes the morphogenesis and cytological characteristics of 'branched absorbing structures' (BAS, formely named arbuscule-like structures, ALS), small groups of dichotomous hyphae formed by the extraradical mycelium of arbuscular mycorrhizal (AM) fungi. Monoxenic cultures of the AM fungus Glomus intraradices Smith & Schenck and tomato ( Lycopersicum esculentum Mill.) roots allowed the continuous, non-destructive study of BAS development. These structures were not observed in axenic cultures of the fungus under different nutritional conditions or in unsuccessful (asymbiotic) monoxenic cultures. However, extraradical mycelium of G. intraradices formed BAS immediately after fungal penetration of the host root and establishment of the symbiosis. The average BAS development time was 7 d under our culture conditions, after which they degenerated, becoming empty septate structures. Certain BAS were closely associated with spore formation, appearing at the spore's substending hypha. Branches of these spore-associated BAS (spore-BAS) usually formed spores. Electron microscopy studies revealed that BAS and arbuscules show several ultrastructural similarities. The possible role of BAS in nutrient uptake by the mycorrhizal plant is discussed.