Effect of free-soil-inhabiting or root-associated microfungi on the development of arbuscular mycorrhizæ and on proliferation of intraradical mycorrhizal hyphæ

Colonization of maize roots by the arbuscular mycorrhizal fungusGlomus fistulosum and proliferation of intraradical distributive hyphæ was influenced by the free-soil-inhabiting sterile microfungus SC. Inoculation with this isolate significantly increased the percentage of the infected root length and changed the composition of population of microfungi in the cultivation substratum. Compared to a control without inoculation with any saprophytic microfungus, inoculation with the isolate SC significantly (by approx. 100%) increased the percentage of root segments showing the proliferation of mycorrhizal fungus, the mean number of proliferating hyphæ per active (proliferating) root segment being increased by approx. 200%. The plant growth was not affected by inoculation with any of the saprophytes tested.     

培养容器容积对AM真菌生长发育的影响

研究宿主植物栽培容器对丛枝菌根(Arbuscularmycorrhizae,AM)真菌Glomusmosseae生长发育的影响。结果表明:小容积容器的根系密度相对较大,在菌根共生体建立初期,菌根真菌繁殖体与根接触的机会增大,对于菌根真菌的迅速侵染及共生体的迅速建立非常有利,同时还增大了根外菌丝二次侵染的机会,从而使菌根真菌生长发育形成了一个良性循环,最终有利于根外孢子的形成。容器对共生体的影响决不是简单的盆的体积问题,而与其面积和体积之比有关,也和种植密度有密切关系。     

Effects of water stress, organic amendment and mycorrhizal inoculation on soil microbial community structure and activity during the establishment of two heavy metal-tolerant native plant species

Our aim was to examine the effect of water stress on plant growth and development of two native plant species (Tetraclinis articulata and Crithmum maritimum) and on microbial community composition and activity in the rhizosphere soil, following the addition of an organic amendment, namely sugar beet residue (SBR), and/or the inoculation with an arbuscular mycorrhizal (AM) fungus, namely Glomus mosseae, in a non-sterile heavy metal-polluted soil. The AM inoculation did not have any significant effect on plant growth of both species. In T. articulata, SBR increased shoot growth, foliar P, total phospholipid fatty acids (PLFA), fungi-related PLFA, AM fungi-related neutral lipid fatty acid, bacterial gram-positive/gram-negative PLFA ratio and the β-glucosidase and dehydrogenase activities. SBR and AM inoculation increased phosphatase activity in T. articulata plants grown under drought conditions. In both plants, there was a synergistic effect between AM inoculation and SBR on mycorrhizal colonisation under drought conditions. In C. maritimum, the increase produced by the SBR on total amounts of PLFA, bacterial gram-positive-related PLFA and bacterial gram-negative-related PLFA was considerably higher under drought conditions. Our results suggest that the effectiveness of the amendment with regard to stimulating microbial communities and plant growth was largely limited by drought, particularly for plant species with a low degree of mycorrhizal colonisation.     

丛枝菌根真菌对枳根净离子流及锌污染下枳苗矿质营养的影响

盆栽实验研究了不同施Zn水平(0、300 mg/kg和600 mg/kg)下,接种丛枝菌根真菌Glomus intraradices对枳苗生长、Zn、Cu、P、K、Ca、Mg分布的影响,并采用非损伤微测技术测定分析了菌根化与非菌根化枳根净Ca²⁺、H⁺、NO₃^-离子流动态。结果表明:(1)在不同施Zn水平下,接种菌根真菌显著提高了枳苗地上部及根部鲜重;随着施Zn水平的提高,菌根侵染率呈降低趋势,枳苗地上部与根部Zn含量呈增加趋势,且接种株根部Zn含量显著高于未接种株。(2)接种株未施Zn处理的地上部Cu、P、K、Mg和根部Cu含量、施600 mg/kg Zn处理的根部Cu及施300 mg/kg Zn处理的根部P含量均显著高于对照,而菌根真菌侵染对枳苗Ca含量并无显著性影响。(3)接种株未施Zn处理的根部距根尖端0 μm和600 μm处净Ca²⁺流出速率、600 μm处净H⁺流入速率、2400 μm处净NO₃^-流入速率均显著高于未接种株。     

Interaction between arbuscular mycorrhizal fungus Glomus mosseae and plant growth promoting fungus Phoma sp. on their root colonization and growth promotion of cucumber (Cucumis sativus L.)

Interaction between arbuscular mycorrhizal fungus Glomus mosseae and plant growth promoting fungus Phoma sp. was studied for its effect on their root colonization and plant growth of cucumber. Two isolates of Phoma sp. (GS8-2 and GS8-3) were tested with G. mosseae. The percent root length colonized by G. mosseae was not adversely affected by the presence of Phoma isolates. In contrast, the root colonization of both isolates GS8-2 and GS8-3 in 4-week-old plants was significantly reduced (80.7% and 84.3%, respectively) by added G. mosseae. Inoculating plants with each Phoma isolate significantly increased the shoot dry weight. However, dual inoculation of each Phoma isolate with G. mosseae had no significant effect on growth enhancement.     

Influence of bacterial strains isolated from lead-polluted soil and their interactions with arbuscular mycorrhizae on the growth of Trifolium pratense L. under lead toxicity

We isolated two bacterial strains from an experimentally lead (Pb)-polluted soil in Hungary, 10 years after soil contamination. These strains represented the two most abundant cultivable bacterial groups in such soil, and we tested their influence on Trifolium pratense L. growth and on the functioning of native mycorrhizal fungi under Pb toxicity in a second Pb-spiked soil. Our results showed that bacterial strain A enhanced plant growth, nitrogen and phosphorus accumulations, nodule formation, and mycorrhizal infection, demonstrating its plant-growth-promoting activity. In addition, strain A decreased the amount of Pb absorbed by plants, when expressed on a root weight basis, because of increased root biomass due to the production of indoleacetic acid. The positive effect of strain A was not only evident after a single inoculation but also in dual inoculation with arbuscular mycorrhizal fungi. Strain A also exhibited higher tolerance than strain B when cultivated under increasing Pb levels in the spiked soil. Molecular identification unambiguously placed strain A within the genus Brevibacillus. We showed that it is important to select the most tolerant and efficient bacterial strain for co-inoculation with arbuscular mycorrhizal fungi to promote effective symbiosis and thus stimulate plant growth under adverse environmental conditions, such as heavy-metal contamination.     

Influence of arbuscular mycorrhizal fungi on microbes and enzymes of soils from different cultivated densities of red clover

Effects of arbuscular mycorrhizal fungus (AMF)Glomus mosseae on plant growth, soil microbial populations and enzymes activities of soils were studied in red clover (Trifolium pratense L.) grown in pots at different cultivated densities. Seeds of red clover were sown with 50 g inoculums ofG. mosseae per pot. After a week, the plants were thinned to 20, 30, 40, 50 and 60 seedlings per pot. Three months after treatment, AMF inoculation significantly stimulated plant growth. Quantities of vesicles and spores, arbuscules and hyphae were the highest when 30 and 50 seedlings were grown per pot, respectively. However, no root was infected in control plants. In all the soil sites, the numbers of fungi and bacteria were followed in the order: root > root surface > rhizospheric. It was indicated that arbuscular mycorrhizal fungus decreased the numbers of fungi and bacteria but improved growth of actinomycetes. Compared to control plants, AMF stimulated activities of phosphatase and urease but decreased invertase.     

丛枝菌根真菌摩西管柄囊霉侵染增强番茄对机械损伤的响应

植食性昆虫取食会给植物造成机械损伤并激活植物的防御反应,而与有益微生物共生是否可以增强植物对机械损伤的响应对植物抗虫有重要意义.本研究在番茄根系被丛枝菌根真菌摩西管柄囊霉侵染后,研究机械损伤对番茄防御反应的影响.结果表明: 预先接种菌根真菌的番茄叶片受到机械损伤处理(FD)后,叶片苯丙氨酸解氨酶(PAL)、超氧化物歧化酶(SOD)、过氧化物酶(POD)、多酚氧化酶(PPO)和过氧化氢酶(CAT)活性,以及叶片和根系苯丙氨酸解氨酶基因(PAL)和β-1,3-葡聚糖酶基因(PR2)的转录水平均显著高于只进行机械损伤的处理(D)、只接种摩西管柄囊霉的处理(F),以及既未接种菌根菌也未进行机械损伤的健康番茄植株(CK).虽然D和 F处理也可诱导部分酶活性及基因转录水平升高,但FD处理诱导的防御反应更迅速和强烈.表明丛枝菌根真菌侵染可以警备(prime)番茄对机械损伤做出更快速和强烈的响应.     

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.     

Growth response of threeFestuca rubra clones to light quality and arbuscular mycorrhiza

The influence of the arbuscular mycorrhizal fungus—Glomus etunicatum and changes in light quality (decrease of red/far-red ratio) on the growth of threeFestuca rubra clones, ecotypes originating from a mountain grassland region, was studied in a growth chamber experiment. Inoculation with the arbuscular mycorrhizal fungus and low red/far-red ratio decreased both the number of tillers and the biomass of treated plants. Significant interactions between the treatments were found and most of the growth characteristics were reduced further when both treatments were applied simultaneously. Inoculation with the arbuscular mycorrhizal fungus also resulted in reduced maximum height of tillers, whereas low red/far-red ratio caused the maximum height of tillers to increase. Differences in plasticity were found for the threeFestuca rubra clones. Response to one treatment was strongly modified by the other treatment. This indicates that the arbuscular mycorrhizal fungus and red/far-red ratio can differentially influence the growth ofFestuca rubra clones and thus modify their relative competitive abilities which can consequently have implications for the coexistence mechanisms within plant population, thereby potentially influencing plant canopy and community structure.     

缺铁和过量重碳酸盐胁迫下丛枝菌根真菌对枳活性氧代谢的影响

采用盆栽沙培试验,研究了缺铁处理及重碳酸盐胁迫下丛枝菌根真菌地表球囊霉对枳实生苗抗活性氧系统的影响。试验结果表明,在缺铁以及重碳酸盐胁迫处理下,丛枝菌根真菌显著提高了枳叶片和根系中可溶性蛋白含量、超氧化物岐化酶活性、过氧化物酶活性和过氧化氢酶活性,明显增强了叶片类胡萝卜素含量,显著降低了枳叶片和根系中的丙二醛含量,增强了枳自身防御能力,减少了胁迫对枳细胞膜的伤害。     

Arbuscular mycorrhizal fungus-promoted accumulation of two new triterpenoids in cucumber roots

Cucumber (Cucumis sativus L.) roots were analyzed by HPLC and TLC for their levels of secondary metabolites upon inoculation with the arbuscular mycorrhizal fungus, Glomus caledonium. Three compounds in EtOAc extracts from the mycorrhizal roots showed significant increases six weeks after inoculation. These compounds were isolated by column chromatography and determined to be two novel triterpenes, 2beta-hydroxybryonolic acid (2beta,3beta-dihydroxy-D:C-friedoolean-8-en-29-oic acid) and 3beta-bryoferulic acid [3beta-O-trans-ferulyl-D:C-friedooleana-7,9(11)-diene-29-oic acid], and the known triterpene, bryonolic acid, by spectroscopic methods. Time-course experiments showed that the levels of the three terpenoids in cucumber roots were significantly increased by the application of a 53-microm sieving from a soil inoculum of the arbuscular mycorrhizal fungus containing soil microbes but no mycorrhizal fungi, and that mycorrhizal colonization further promoted the terpenoid accumulation. Inoculation with Glomus mosseae also enhanced the accumulation of the triterpenes, whereas no accumulation was observed by inoculating with the fungal pathogen, Fusarium oxysporum f. sp. cucumerinum. 2Beta-hydroxybryonolic acid was also isolated from the roots of melon and watermelon.     

Arbuscular Mycorrhizal Symbiosis Changes the Colonization Pattern of Acacia tortilis spp. Raddiana Rhizosphere by Two Strains of Rhizobia

The aim of the study was to assess the effect of the mycorrhizosphere of A. tortillis spp. raddiana mycorrhized with Glomus intraradices on the root nodulation by Sinorhizobium terangae (ORS 1009) and/or Mesorhizobium plurifarium (ORS 1096) in two different culture substrates (sandy soil and sand). The endomycorrhizal fungus only stimulated plant growth in the sandy soil. Moreover, arbuscular mycorrhizal infection enhanced the nodulation process in both culture substrates. Beside the stimulatory effects of the mycorrhizosphere on both rhizobia development, fungal symbiosis induces two different dynamics of each bacterial strains in the sand-grown plants. These results suggest specific relationships could occur during the development of the tripartite symbiosis, at physiological and molecular level. From a practical point of view, the role of arbuscular mycorrhizas in improving nodulation and N2 fixation is universally recognized. The fungal symbiosis could modify the development of bacterial inoculants along the root systems. This effect is of particular interest in the controlled inoculation of selected rhizobia.     

丛枝菌根真菌对枳根系形态和蔗糖、葡萄糖含量的影响

研究丛枝菌根真菌接种(摩西球囊霉、地表球囊霉和摩西球囊霉+地表球囊霉)对盆栽枳的生长、根系形态以及蔗糖、葡萄糖含量的影响.结果表明: 3个接种处理都显著提高枳的株高、茎粗、叶片数,以及地上部和地下部生物量,诱导1级、2级和3级侧根的发生,同时增加了根系投影面积、表面积、体积和总长度(主要是0～1 cm根长),但降低根系平均直径,其中以地表球囊霉效果最明显.丛枝菌根真菌接种显著提高枳的叶片蔗糖和根系葡萄糖含量,但降低叶片葡萄糖和根系蔗糖含量.由于根系“菌根碳库”的存在,丛枝菌根真菌接种导致根系维持较高的葡萄糖和较低的蔗糖含量,从而有利于宿主根系的生长和发育,建立更优的根系形态.     

Arbuscular mycorrhizal fungal application to improve growth and tolerance of wheat (Triticum aestivum L.) plants grown in saline soil

A pot experiment was conducted to examine the effects of three different arbuscular mycorrhizal fungi, Glomus mosseae, G. deserticola and Gigaspora gergaria, on growth and nutrition of wheat (Triticum aestivium L. cv. Henta) plants grown in saline soil. Under saline condition, mycorrhizal inoculation significantly increased growth responses, nutrient contents, acid and alkaline phosphatases, proline and total soluble protein of wheat plants compared to non-mycorrhizal ones. Those stimulations were related to the metabolic activity of the each mycorrhizal fungus. The localization of succinate dehydrogenase “SDH” (as a vital stain for the metabolically active fungus) in the arbuscular mycorrhizal fungi was variable. In general, mycorrhizal shoot plant tissues had significantly higher concentrations of P, N, K and Mg but lower Na concentration than those of non-mycorrhizal plants. In saline soil, growth and nutrition of wheat plants showed a high degree of dependency on mycorrhizal fungi (especially G. mosseae). The use of the nitroblue tetrazolium chloride method as a vital stain for SDH activity showed that all the structures of mycorrhizal infections in the wheat plant estimated by the trypan blue staining (non-vital stain) were not metabolically active. Interestingly, the reduction in Na uptake along with associated increases in P, N and Mg absorption and high proline, phosphatase activities and chlorophyll content in the mycorrhizal plants could be important for salt alleviation in plants growing in saline soils.     

水分胁迫下丛枝菌根真菌对枳实生苗生长和渗透调节物质含量的影响

采用盆栽试验研究了水分胁迫下接种丛枝菌根真菌摩西球囊霉(Glomaus mosseae)对枳[Poncirustrifoliat(L.)Raf.]实生苗的生长和渗透调节物质含量的影响.结果表明,在土壤含水量为20%、16%和12%条件下,接种G.mosseae能够增加植株的生长(株高、茎粗、叶面积、地上部干重、地下部干重和植株干重),促进植株根系活跃吸收面积和根际土壤有效磷的吸收,提高叶片和根系可溶性糖含量的积累,降低叶片脯氨酸含量,增强植株的水分利用效率(达20%～40%),使枳实生苗的抗旱能力得到增强.土壤含水量为20%和16%条件下接种G.mosseae对植株的效果较土壤含水量为12%条件下更显著.12%的土壤含水量严重抑制Gmosseae的侵染,说明丛枝菌根侵染程度轻,其对植物的效果也差.     

Presymbiotic growth and sporal morphology are affected in the arbuscular mycorrhizal fungus Gigaspora margarita cured of its endobacteria

Some arbuscular mycorrhizal fungi contain endocellular bacteria. In Gigaspora margarita BEG 34, a homogenous population of beta-Proteobacteria is hosted inside the fungal spore. The bacteria, named Candidatus Glomeribacter gigasporarum, are vertically transmitted through fungal spore generations. Here we report how a protocol based on repeated passages through single-spore inocula caused dilution of the initial bacterial population eventually leading to cured spores. Spores of this line had a distinct phenotype regarding cytoplasm organization, vacuole morphology, cell wall organization, lipid bodies and pigment granules. The absence of bacteria severely affected presymbiotic fungal growth such as hyphal elongation and branching after root exudate treatment, suggesting that Ca. Glomeribacter gigasporarum is important for optimal development of its fungal host. Under laboratory conditions, the cured fungus could be propagated, i.e. could form mycorrhizae and sporulate, and can therefore be considered as a stable variant of the wild type. The results demonstrated that - at least for the G. margarita BEG 34 isolate - the absence of endobacteria affects the spore phenotype of the fungal host, and causes delays in the growth of germinating mycelium, possibly affecting its ecological fitness. This cured line is the first manipulated and stable isolate of an arbuscular mycorrhizal fungus.     

Cadmium accumulation and buffering of cadmium-induced stress by arbuscular mycorrhiza in three Pisum sativum L. genotypes

The role of arbuscular mycorrhiza in reducing Cd stress was investigated in three genotypes of Pisum sativum L. (cv. Frisson, VIR4788, VIR7128), grown in soil/sand pot cultures in the presence and absence of 2-3 mg kg(-1) bioavailable Cd, and inoculated or not with the arbuscular mycorrhizal fungus Glomus intraradices. Shoot, root and pod biomass were decreased by Cd in non-mycorrhizal plants. The presence of mycorrhiza attenuated the negative effect of Cd so that shoot biomass and activity of photosystem II, based on chlorophyll a fluorescence, were not significantly different between mycorrhizal plants growing in the presence or absence of the heavy metal (HM). Total P concentrations were not significantly different between mycorrhizal and non-mycorrhizal plants treated with Cd. From 20-50-fold more Cd accumulated in roots than in shoots of Cd-treated plants, and overall levels were comparable to other metal-accumulating plants. Genetic variability in Cd accumulation existed between the pea genotypes. Concentration of the HM was lowest in roots of VIR4788 and in pods of VIR4788 and VIR7128. G. intraradices inoculation decreased Cd accumulation in roots and pods of cv. Frisson, whilst high concentrations were maintained in roots and pods of mycorrhizal VIR7128. Shoot concentrations of Cd increased in mycorrhizal cv. Frisson and VIR4788. Sequestration of Cd in root cell walls and/or cytoplasm, measured by EDS/SEM, was comparable between non-mycorrhizal pea genotypes but considerably decreased in mycorrhizal cv. Frisson and VIR7128. Possible mechanisms for mycorrhiza buffering of Cd-induced stress in the pea genotypes are discussed.     

Contribution of an arbuscular mycorrhizal fungus to the uptake of cadmium and nickel in bean and maize plants

Two experiments were carried out in pots with three compartments, a central one for root and hyphal growth and two outer ones which were accessible only for hyphae of the arbuscular mycorrhizal fungus, Glomus mosseae ([Nicol. and Gerd.] Gerdemann and Trappe). In the first experiment, mycorrhizal and nonmycorrhizal bean (Phaseolus vulgaris L.) plants were grown in two soils with high geogenic cadmium (Cd) or nickel (Ni) contents. In the second experiment, mycorrhizal and nonmycorrhizal maize (Zea mays L.) or bean plants were grown in a non-contaminated soil in the central compartment, and either the Cd- or Ni-rich soil in the outer compartments. In additional pots, mycorrhizal plants were grown without hyphal access to the outer compartments. Root and shoot dry weight was not influenced by mycorrhizal inoculation, but plant uptake of metals was significantly different between mycorrhizal and nonmycorrhizal plants. In the first experiment, the contribution of mycorrhizal fungi to plant uptake accounted for up to 37% of the total Cd uptake by bean plants, for up to 33% of the total copper (Cu) uptake and up to 44% of the total zinc (Zn) uptake. In contrast, Ni uptake in shoots and roots was not increased by mycorrhizal inoculation. In the second experiment, up to 24% of the total Cd uptake and also up to 24% of the total Cu uptake by bean could be attributed to mycorrhizal colonisation and delivery by hyphae from the outer compartments. In maize, the mycorrhizal colonisation and delivery by hyphae accounted for up to 41% of the total Cd uptake and 19% of the total Cu uptake. Again, mycorrhizal colonisation did not contribute to Ni uptake by bean or maize. The results demonstrate that the arbuscular mycorrhizal fungus contributed substantially not only to Cu and Zn uptake, but also to uptake of Cd (but not Ni) by plants from soils rich in these metal cations. Deceased 21 September 1996 Deceased 21 September 1996     

A phosphate transporter gene from the extra-radical mycelium of an arbuscular mycorrhizal fungus Glomus intraradices is regulated in response to phosphate in the environment

The majority of vascular flowering plants are able to form symbiotic associations with arbuscular mycorrhizal fungi. These symbioses, termed arbuscular mycorrhizas, are mutually beneficial, and the fungus delivers phosphate to the plant while receiving carbon. In these symbioses, phosphate uptake by the arbuscular mycorrhizal fungus is the first step in the process of phosphate transport to the plant. Previously, we cloned a phosphate transporter gene involved in this process. Here, we analyze the expression and regulation of a phosphate transporter gene (GiPT) in the extra-radical mycelium of the arbuscular mycorrhizal fungus Glomus intraradices during mycorrhizal association with carrot or Medicago truncatula roots. These analyses reveal that GiPT expression is regulated in response to phosphate concentrations in the environment surrounding the extra-radical hyphae and modulated by the overall phosphate status of the mycorrhiza. Phosphate concentrations, typical of those found in the soil solution, result in expression of GiPT. These data imply that G. intraradices can perceive phosphate levels in the external environment but also suggest the presence of an internal phosphate sensing mechanism.