Development Of Arbuscular Mycorrhizal Fungi Research Articles

Co-entrapment of Trichoderma harzianum and Glomus sp. within alginate beads: impact on the arbuscular mycorrhizal fungi life cycle

This study was performed to explore the compatibility and applicability of plant beneficial micro-organisms (i.e. Trichoderma harzianum MUCL 29707 and Glomus sp. MUCL 41833) co-entrapped in alginate beads. Spores of Glomus sp. and conidia of T. harzianum were immobilized in alginate beads and the impacts of the saprotrophic fungi on the presymbiotic and symbiotic phase of the arbuscular mycorrhizal (AM) fungi evaluated under strict in vitro culture conditions. Our results demonstrated the capacity of both micro-organisms in combination to regrowth outside the calcium alginate coating. The presence of T. harzianum did not hinder the AM fungal development but rather stimulated its spore production and fitness. The combination of T. harzianum MUCL 29707 with Glomus sp. MUCL 41833 in alginate beads may represent a reliable alternative inoculum formulation for application in sustainable agriculture. The entrapment in the alginate beads of two fungi (i.e. a saprotroph and a symbiont) having beneficial effects on plants represents a promising formulation for the development of inoculants adapted to field application.

Establishment of Mycorrhizas of Four Different Species of Arbuscular Mycorrhizal Fungi Observed Using Petri-Dish Microcosm

The Petri-dish microcosm is a simple system to study the development of arbuscular mycorrhizal fungi (AMF) and has been shown to be suitable to observe the establishment of Acaulospora tuberculata BEG41, Gigaspora rosea BEG111, Glomus manihotis BEG112 and Scutellospora heterogama BEG40 on plant root. The non-agar based system could be easily used to observe the whole course of development of fungal-root interactions as well as the extra-radical structures of AMF without destructive sampling.  It was found that these AMF species were unique with regard to spore germination, root colonization, the architecture of the extra-radical mycelium (ERM), the spread of the ERM in the media, and sporulation.  The ERM of A. tuberculata BEG41and G. manihotis BEG112 spread mainly close to the root system, while the ERM of G. rosea BEG111 and S. heterogama  BEG40 could occupy areas unoccupied by roots.  The unique structure, the branch absorbing structure, was found in the four species of AMF, but differed in their shape and size

The interactive effect of an AM fungus and an organic amendment with regard to improving inoculum potential and the growth and nutrition of Trifolium repens in Cd-contaminated soils

Aspergillus niger-treated dry olive cake (DryOC) can be used as a soil organic amendment and the aim of this work was to study the effectiveness of this amendment and a Cd-adapted arbuscular mycorrhizal (AM) fungus in improving Trifolium repens growth and nutrition in Cd-contaminated soil. In a compartmentalized growth system, consisting of a root compartment (RC) and two hyphal compartments (HCs), we investigated the influence of the amendment on intraradical and extraradical AM fungi development. In addition, we studied the viability and infectivity of the detached extraradical mycelium in plants, designated as receptor plants, grown in the HC after removal of the RC. Both the amendment and the AM fungus increased shoot and root biomass and nodulation in both the non-contaminated and Cd-contaminated soils. The positive interaction between the microbiologically treated DryOC and the AM fungus resulted in the highest plant yield, which can be explained by enhanced nutrient acquisition and arbuscular richness as well as by the immobilisation of Cd in amended soils. However, A. niger-treated DryOC had no effect on the extraradical mycorrhizal mycelium development. Although Cd decreased AM hyphal length density, symbiotic infectivity was similar in receptor plants grown in non-contaminated and contaminated soil, thus confirming the AM fungal inoculum potential. The combination of the AM fungus and A. niger-treated DryOC increased plant tolerance to Cd in terms of plant growth and nutrition and can be regarded as an important strategy for reclaiming Cd-contaminated soils.

Effect of polyamine on growth and development of arbuscular mycorrhizal fungi and host plant in symbiotic culture condition

The effects of exogenous polyamine on the growth and development of arbuscular mycorrhizal fungi (AMF) and host plant in the symbiotic culture condition were investigated by micropropagating grape plantlets infected with AMF (Gigaspora margarita) and then treated with exogenous polyamine (PA) and polyamine biosynthesis inhibitor [methylglyoxal bis (guanylhydrazone), MGBG]. The effects of exogenous PA and MGBG on spore germination, hyphal growth of AMF and development of the host plant in symbiotic culture condition were analyzed. The results indicate that certain doses of exogenous PA have significant effect on symbiotic development, grape plantlets and AMF. AMF arbuscular abundance, hyphal length, spore number and infection rate increase after treatment with exogenous PA. Meanwhile, PA biosynthesis inhibitor (MGBG) has opposite effect which is suppressed by application of exogenous PA. This implies that PA also has significant stimulating effect on the growth and development of AMF in ex vitro conditions. Because exogenous PA activates AMF in the rhizosphere, potential AMF infection is enhanced. Thus, AMF symbiotic association with grape plantlets can establish at early weaning stage and develop with time.

Does the sequence of plant dominants affect mycorrhiza development in simulated succession on spoil banks?

The aim of this field study was to examine how the development of arbuscular mycorrhizal fungi (AMF) on coal mine spoil banks is affected by the presence of plants with different mycorrhizal status. A 3-year trial was conducted on the freshly created spoil bank Vrsany, North-Bohemian coal basin, the Czech Republic. Three plant species – non-mycotrophic annual Atriplex sagittata, highly mycotrophic annual Tripleurospermum inodorum (both dominants of early stages of succession) and facultatively mycotrophic Arrhenatherum elatius (a perennial grass species of the later stage of succession) – were planted on 1 m2 plots over 3 years in different sequences that simulated the progress of succession on spoil banks. The development of AMF populations was monitored by evaluation of mycorrhizal colonization of plant roots and by measurement of the mycorrhizal inoculation potential (MIP) of soil. These two parameters were compared between plots inoculated with the mixture of three AMF isolates – Glomus mosseae BEG95, G. claroideum BEG96 and G. intraradices BEG140 – (“inoculated plots”) and plots exposed only to natural dispersal of AMF propagules (“uninoculated plots”). Highly colonized roots of plants together with a high MIP of soil in uninoculated plots were already found at the end of the first season, indicating rapid natural dispersal of AMF propagules. Root colonization of facultatively mycotrophic and non-mycotrophic plants in later years was affected by the mycorrhizal status of the previous plant species. The MIP of soil continuously increased throughout the experiment; in uninoculated plots, the MIP was temporarily decreased if plant species of higher mycotrophy were replaced by species of lower mycotrophy. The results lead to the conclusion that AMF colonize freshly formed sites very quickly and reproduce or accumulate in the soil, which leads to increasing MIP values. However, this infective potential can be decreased if non-mycotrophic plants predominate on the site.

The effect of EDDS chelate and inoculation with the arbuscular mycorrhizal fungus Glomus intraradices on the efficacy of lead phytoextraction by two tobacco clones

Two pot experiments were conducted to investigate the effect of inoculation with the arbuscular mycorrhizal (AM) fungus Glomus intraradices on Pb uptake by two clones of Nicotiana tabacum plants. Non-transgenic tobacco plants, variety Wisconsin 38, were compared in terms of Pb uptake with transgenic plants of the same variety with inserted gene coding for polyhistidine anchor in fusion with yeast metallothionein. Bioavailability of Pb in experimentally contaminated soil was enhanced by the application of a biodegradable chelate ethylenediaminedissuccinate (EDDS). EDDS addition (2.5 and 5.0 mmol kg −1 substrate) increased Pb uptake from the substrate and enhanced Pb translocation from the roots to the shoots, with shoot Pb concentrations reaching up to 800 mg kg −1 at the higher chelate dose. Application of a single dose of 5 mmol kg −1 proved to be more efficient at increasing shoot Pb concentrations than two successive doses of 2.5 mmol kg −1, in spite of a marked negative effect on plant growth and phytotoxicity symptoms. Pb amendment (1.4 g kg −1 substrate) connected with either dose of EDDS decreased significantly plant biomass as well as reduced the development of AM fungi. AM inoculation promoted the growth of tobacco plants and partly alleviated the negative effect of Pb contamination, mainly in the case of root biomass. No consistent difference in Pb uptake was found between transgenic and non-transgenic tobacco plants. The effect of AM inoculation on Pb concentrations in plant biomass varied between experiments, with no effect observed in the first experiment and significantly higher root Pb concentrations and increased root–shoot ratio of Pb concentrations in the biomass of inoculated plants in the second experiment. Due to probable retention of Pb in fungal mycelium, the potential of AM for phytoremediation resides rather in Pb stabilisation than in phytoextraction.

EFFECTS OF ARBUSCULAR MYCORRHIZAL FUNGI ON PLANT SECONDARY METABOLISM

Mycorrhizal fungi form the most important mutualistic symbioses on earth with plants. The most prevalent type of mycorrhizal fungi are the arbuscular mycorrhizal (AM) fungi. Much research has shown that the development of AM fungi is correlated with plant secondary metabolism. AM fungi can directly or indirectly affect plant secondary metabolic processes. Secondary metabolites are classified into 3 groups, terpenoids, phenolics and alkaloids. In this paper, we summarize the effects of AM fungi on the 3 groups of secondary metabolites. The relationship between terpenoids and AM fungi have been well studied, and some research has explored interactive mechanisms at the molecular level. Blumenin was first isolated and identified from mycorrhizal cereals, and its biosynthesis has been proven via the Glyceraldehyde 3_phosphate/ pyruvate pathway (MEP) by an isotopic labeling method. Since then, the accumulation of blumenin induced by AM fungi and differences in blumenin levels among different kinds of AM fungi have been observed. Studies on 1_deoxy_D_xylulose_5_phosphate synthase (DXS) and 1_deoxy_D_xylulose_5_phosphate reductoisomerase (DXR), two key enzymes in the biosynthesis of carotenoid metabolism via the MEP pathway, have found to increase the transcription of DXS and DXR in plants with AM fungi. Moreover it was temporarily and spatially correlated with the accumulation of apocarotenoids. Subsequently, two genes were identified: TC78589 encoding DXS2 which is highly expressed in roots inoculated with AM fungi, and TC77051 encoding mevalonate disphosphate decarboxylase, which is catalysed in the synthesis of terpenoids in the mevalonate pathway. Although both genes separately encode enzymes in different pathways, an enhancement of carotenoid biosynthesis has been observed. The interaction between phenolic compounds (such as phytoalexin, wall_bound phenol, flavonoids, isoflavonoids and their derivatives) and AM fungi also has been investigated intensively. It has been shown that some flavonoids stimulated the spore germination and hyphal growth of AM fungi, and the contents of flavonoids increased before the infection of AM fungi. Therefore some investigators hypothesized that flavonoids were a signal compound during the formation of AM fungi. Afterward, increased levels of flavonoids were found after the formation of AM fungi which was related to specific species of AM fungi. In addition, some experiments have indicated that the activity of peroxidase (POD), phenylalanine ammonia_lyase (PAL) and polyphenol oxidase (PPO) were significantly enhanced in AM plants. In phenylpropamoid metabolism, there are two different signaling pathways in the accumulation of secondary metabolites induced by the mycorrhizal fungus: one is through the induction of PAL and chalcone synthase (CHS), and the other is through the suppression of isoflavone reductase (IFR).Although little research seldom has examined the relationship between alkaloids and AM fungi, a recent study has shown that the formation of AM is beneficial to the accumulation of alkaloids. This study also showed the species specificity in AM affected biosynthesis of alkaloids.

Growth and development of AM fungi and maize under salt and acid stress

The growth and development of Arbuscular mycorrhizal fungi and maize as a response to salt and acid stress was studied. Maize plants were placed under salt stress by supplementing NaCl (3%) and acid stress by HCl under inoculated conditions. Plant growth was reduced by almost 50% compared with uninoculated control plants under the NaCl treatment. AM colonization in terms of percentage and number of vesicles/root and spore count in the soils was also reduced in this treatment. NaCl treatment was found to be inhibitory for the development and growth of maize as well as Arbuscular mycorrhizal fungi. Overall, maize plants showed reduced rate of growth in acid treatments, apart from root dry weight. No mycorrhization was, however, detected in the acid treated maize plants.

Effect of Azospirillum inoculants on arbuscular mycorrhiza establishment in wheat and maize plants

Plant growth-promoting rhizobacteria and arbuscular mycorrhizal (AM) fungi represent two main groups of beneficial microorganisms of the rhizosphere. The role of different strains of Azospirillum on AM fungi development was evaluated by measuring the percentage of AM colonisation of the root system in durum wheat and maize plants, grown under both greenhouse and field conditions. The effect of wild-type Azospirillum brasilense strain Sp245 and genetically modified (GM) derivatives overproducing indole-3-acetic acid was assessed at greenhouse level in (1) three different cultivars of durum wheat, in the presence of indigenous AM fungi and (2) maize plants artificially inoculated with Glomus mosseae and Glomus macrocarpum. In addition, the establishment of natural AM fungal symbiosis was evaluated using Azospirillum lipoferum CRT1 in maize plants at field level. Despite the stimulatory effect of the different Azospirillum inocula on root growth, no significant differences in AM colonisation were found, independently of the AM fungus involved, either in wheat or in maize plants. Similarly, GM A. brasilense, which strongly stimulates root development, did not affect AM formation. Although these results were obtained in conditions in which the mycorrhization rate was moderate (15–30%), overall considered they indicate that the use of wild-type or GM Azospirillum phytostimulators does not alter mycorrhization.

Relationship between Arbuscular Mycorrhizal Fungal Development and Eupalitin Content in Bahiagrass Roots Grown in a Satsuma Mandarin Orchard

An experiment was carried out in a satsuma mandarin orchard with a bahiagrass (Paspalum notatum Fliigge.) covercrop to evaluate if the concentration of eupalitin, a growth stimulatory compound for arbuscular mycorrhizal (AM) fungi, is correlated with AM fungal development in soils. Root and soil samples were obtained monthly from the satsuma mandarin and bahiagrass to evaluate the AM infection in the roots and the number of AM spores in the soil. The root samples were kept in a freezer until analysed for eupalitin. Eupalitin was isolated and purified from bahiagrass root extracts by flash chromatography, gel filtration, and high pressure liquid chromatography (HPLC) and its concentration in each sample was determined based on a standard solution. The percentage of AM infection in both bahiagrass and satsuma mandarin roots was around 80% during the summer but decreased from October. The number of spores started to increase in March, attaining a maximum of around 800 in 25 g soil in June; the count subsequently decreased. Eupalitin concentration in bahiagrass roots was high from May to November, peaking in May and July. The concentration of eupalitin was significantly correlated with the AM infection in bahiagrass and the number of spores in soil, but not for the AM infection in satsuma mandarin. It suggests that there might be an interaction between AM fungal development and growth stimulatory compounds in soil.

Fungal lipid accumulation and development of mycelial structures by two arbuscular mycorrhizal fungi.

We monitored the development of intraradical and extraradical mycelia of the arbuscular mycorrhizal (AM) fungi Scutellospora calospora and Glomus intraradices when colonizing Plantago lanceolata. The occurrence of arbuscules (branched hyphal structures) and vesicles (lipid storage organs) was compared with the amounts of signature fatty acids. The fatty acid 16:1omega5 was used as a signature for both AM fungal phospholipids (membrane constituents) and neutral lipids (energy storage) in roots (intraradical mycelium) and in soil (extraradical mycelium). The formation of arbuscules and the accumulation of AM fungal phospholipids in intraradical mycelium followed each other closely in both fungal species. In contrast, the neutral lipids of G. intraradices increased continuously in the intraradical mycelium, while vesicle occurrence decreased after initial rapid root colonization by the fungus. S. calospora does not form vesicles and accumulated more neutral lipids in extraradical than in intraradical mycelium, while the opposite pattern was found for G. intraradices. G. intraradices allocated more of its lipids to storage than did S. calospora. Thus, within a species, the fatty acid 16:1omega5 is a good indicator for AM fungal development. The phospholipid fatty acid 16:1omega5 is especially suitable for indicating the frequency of arbuscules in the symbiosis. We propose that the ratio of neutral lipids to phospholipids is more important than is the presence of vesicles in determining the storage status of AM fungi.

Metal-free cultivation of Glomus sp. BEG 140 isolated from Mn-contaminated soil reduces tolerance to Mn.

The ability of arbuscular mycorrhizal (AM) fungi of different origin and cultivation history to tolerate excessive levels of manganese (Mn) was studied using hydroponic sand culture. Maize plants were colonised with two lineages of Glomus sp. BEG 140 from Mn-contaminated soil kept for 2 years in metal-free substrate or in the original soil. For comparison, the plants were also inoculated with Glomus intraradices BEG 75 from uncontaminated soil or were left uncolonised. Manganese stress was simulated by irrigation with nutrient solutions containing Mn at high concentrations (0.1, 0.5 and 1 mM); control plants were supplied with 3.8 microM Mn. Whereas the growth of maize plants was not suppressed by Mn at the concentrations examined, the development of AM fungi was negatively influenced by the higher Mn concentrations, with significant differences between isolates and cultivation lineages. The isolate Glomus sp. from Mn-contaminated soil showed higher tolerance to Mn than G. intraradices from uncontaminated soil. Colonisation by G. intraradices was reduced by almost 90% when irrigated with 1 mM Mn, whereas colonisation by the Glomus sp. lineage kept in contaminated soil still reached high levels (65% of the colonisation level of the control plants). The lineage of Glomus sp. cultured in inert metal-free substrate tolerated excessive Mn levels to a lesser extent than the lineage kept long-term in the original contaminated soil, but withstood Mn at higher concentrations than the G. intraradices from uncontaminated soil.

The pre-symbiotic growth of arbuscular mycorrhizal fungi is induced by a branching factor partially purified from plant root exudates.

Arbuscular mycorrhizal (AM) symbiosis is an association between obligate biotrophic fungi and more than 80% of land plants. During the pre-symbiotic phase, the host plant releases critical metabolites necessary to trigger fungal growth and root colonization. We describe the isolation of a semipurified fraction from exudates of carrot hairy roots, highly active on germinating spores of Gigaspora gigantea, G. rosea, and G. margarita. This fraction, isolated on the basis of its activity on hyphal branching, contains a root factor (one or several molecules) that stimulates, directly or indirectly, G. gigantea nuclear division. We demonstrate the presence of this active factor in root exudates of all mycotrophic plant species tested (eight species) but not in those of nonhost plant species (four species). We negatively tested the hypothesis that it was a flavonoid or a compound synthesized via the flavonoid pathway. We propose that this root factor, yet to be chemically characterized, is a key plant signal for the development of AM fungi.

Effects of the antimycotic molecule Iturin A2, secreted by Bacillus subtilisstrain M51, on arbuscular mycorrhizal fungi

A new system, devised for the study of early stages of arbuscular mycorrhizal infection, was used to test the effect of the biological control agent Iturin A2, secreted by the strain M51 of Bacillus subtilis, on the development of arbuscular mycorrhizal fungi. The saprophytic growth of the fungus Glomus mosseaewas inhibited by Iturin A2 concentrations higher than 100 g/g of sand; whereas, in the presence of the tomato host plant, both, pre-infection events and intraradical growth were not negatively influenced by the antifungal compound; furthermore, the development of arbuscular mycorrhizal symbiosis was not impeded by the biocontrol agent in field conditions, while Fusarium oxysporumf. sp. lycopersiciinfection was hindered.