Detection of an arbuscular mycorrhizal fungus in roots of different plant species with the PCR.

PCR was used with the primer pair VANS1-NS21 to detect the arbuscular mycorrhizal fungus Glomus intraradices (commercial inoculum source) on roots of lettuce, zinnia, leek, pepper, and endive plants. The appropriate amplification product was obtained directly from roots without DNA extraction and purification.     

Regulation of arbuscular mycorrhizal development by plant host and fungus species in alfalfa

Two cvs of alfalfa ( Medicago sativa L.), Gilboa and Moapa 69, were inoculated in glasshouse pots with three arbuscular mycorrhizal (AM) fungi to investigate the efficacy of mycorrhizas with respect to the extent of colonization and sporulation. Paspalum notatum Flugge also was inoculated to describe fungal parameters on a routine pot culture host. Percentage root length of P. notatum colonized by Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe, Glomus intraradices Schenck & Smith, and Gigaspora margarita Becker & Hall increased from 10 to 21 wk, and all fungi sporulated during that period. In alfalfa, only colonization by G. intraradices increased over that time period, and it was the only fungus to sporulate in association with alfalfa at 10 wk. Glomus mosseae did not sporulate after 16–21 wk despite having colonized 30–35% of the root length of both alfalfa cvs. In vitro experiments in which Ri T-DNA-transformed roots of alfalfa were inoculated with AM fungi showed normal mycorrhizal formation by G. intraradices and a hypersensitivity-like response to Gi. margarita . Colonized cells became necrotic, and HPLC analysis indicated increased concentrations of phenolics and isoflavonoids in these root segments. These data strongly support the existence of a degree of specificity between AM fungi and host that might rely on specific biochemical regulatory processes initiated in the host as a result of the attempts at colonization by the fungus.     

Root colonization of different hosts by the vesicular-arbuscular mycorrhizal fungus Glomus dimorphicum

Colonization of the roots of beans, alfalfa, onions, red clover, corn, and four barley cultivars (Bonanza, Klondike, Gateway 63, and Olli) by Glomus dimorphicum Boyetchko and Tewari, a vesicular-arbuscular mycorrhizal fungus isolated from a barley field in Alberta, Canada, was studied under greenhouse conditions. Infection levels were low in all four barley cultivars but were higher in beans, alfalfa, and onions and were highest in red clover and corn roots. The infection patterns of G. dimorphicum varied among all the hosts. Coiling of intracellular hyphae occurred in corn, alfalfa, and red clover roots. Appreciable numbers of intraradical vesicles were found only in red clover and bean roots, while arbuscules formed in all hosts except barley. It was concluded that the pattern of root colonization by G. dimorphicum is influenced by the host genome and that the fungal morphology in the roots is variable and, thus, not diagnostic for the mycorrhizal species.     

Polyphosphate dynamics in mycorrhizal roots during colonization of an arbuscular mycorrhizal fungus

Inorganic polyphosphate (poly P) has been considered to be a translocatable form of phosphate (Pi) in arbuscular mycorrhizal fungi (AMF). Here we examined time-course changes in poly P content during the AMF colonization process. Onion (Allium cepa) plants were cultured with or without inoculation with Gigaspora margarita for 2-8 wk with periodic sampling. Poly P in the extracts, purified through gel filtration, was quantified by the reverse reaction of polyphosphate kinase. The length of poly P in mycorrhizal roots appeared to be shorter than in extraradical hyphae or in spores of the AMF, indicating that AMF depolymerize poly P before providing Pi to the host. The poly P content increased as colonization proceeded, and was highly correlated with the weight of the colonized roots. These results support the model that AMF supply Pi to the host through the poly P pool, and that the poly P content of a mycorrhizal root can be a good indicator of the Pi-supplying activity of AMF.     

Jasmonates in arbuscular mycorrhizal interactions

The mutualistic interaction between plants and arbuscular mycorrhizal (AM) fungi is believed to be regulated from the plant side among other signals by the action of phytohormones. Evidences for this are based mainly on application experiments and determination of phytohormone levels in AM roots by comparison to non-mycorrhizal roots. In case of jasmonates, additional proof is given by reverse genetic approaches, which led to first insights into their putative role in the establishment and functioning of the symbiosis. This review summarizes the current data about phytohormone action in AM roots and the role of jasmonates in particular.     

Variation in mycorrhizal growth response influences competitive interactions and mechanisms of plant species coexistence

Plant species vary in their growth response to arbuscular mycorrhizal (AM) fungi, with responses ranging from negative to positive. Differences in response to AM fungi may affect competition between plant species, influencing their ability to coexist. We hypothesized that positively responding species, whose growth is stimulated by AM fungi, will experience stronger intraspecific competition and weaker interspecific competition in soil containing AM fungi, while neutrally or negatively responding species should experience weaker intraspecific and stronger interspecific competition. We grew Plantago lanceolata, which responds positively to AM fungi, and Bromus inermis, which responds negatively to AM fungi, in an additive response surface competition experiment that varied the total density and relative frequency of each species. Plants were grown in sterilized background soil that had been inoculated with whole soil biota, which includes AM fungi, or a microbial wash, that contained other soil microbes but no AM fungi, or in sterilized soil that contained no biota. The positively responding P. lanceolata was more strongly limited by intraspecific than interspecific competition when AM fungi were present. By contrast, the presence of AM fungi decreased the strength of intraspecific competition experienced by the negatively responding B. inermis. Because AM fungi are almost always present in soil, strong intraspecific competition in positively responding species would prevent them from outcompeting species that respond neutrally or negatively to AM fungi. The potential for increased intraspecific competition to offset growth benefits of AM fungi could, therefore, be a stabilizing mechanism that promotes coexistence among plant species.     

Chemotropism in the arbuscular mycorrhizal fungus Glomus mosseae

In this work, we report the occurrence of chemotropism in the arbuscular mycorrhizal (AM) fungus Glomus mosseae. Fungal hyphae were able to respond to host-derived signals by reorienting their growth towards roots and to perceive chemotropic signals at a distance of at least 910 microm from roots. In order to reach the source of chemotropic signals, hyphal tips crossed interposed membranes emerging within 1 mm from roots, eventually establishing mycorrhizal symbiosis. The specificity of chemotropic growth was evidenced by hyphal growth reorientation and membrane penetration occurring only in experimental systems set up with host plants. Since pre-symbiotic growth is a critical stage in the life cycle of obligate AM fungal symbionts, chemotropic guidance may represent an important mechanism functional to host root location, appressorium formation and symbiosis establishment.     

The influences of arbuscular mycorrhizal fungus on phytostabilization of lead/zinc tailings using four plant species

A greenhouse experiment was conducted to investigate the effects of the arbuscular mycorrhizal fungus Funneliformis mosseae on three parameters: Pb, Zn, Cu and Cd accumulation, translocation and plant growth in perennial ryegrass (Lolium perenne), tall fescue (Festuca arundinacea), showy stonecrop (Hylotelephium spectabile) and Purple Heart (Tradescantia pallida). The purpose of this work is to enhance site-specific phytostabilization of lead/zinc mine tailings using native plant species. The results showed that mycorrhizal fungi inoculation significantly increased plant biomass of F. arundinacea, H. spectabile and T. pallida. The Pb, Zn, Cu and Cd concentrations in roots were higher than those in shoots both with and without mycorrhizae, with the exception of the Zn concentration in H. spectabile. Mycorrhizae generally increased metal concentrations in roots and decreased metal concentrations in shoots of L. perenne and F. arundinacea. In addition, it was found that the majority of the bioconcentration and translocation factors were lower than 1 and mycorrhizal fungi inoculation further reduced these values. These results suggest that appropriate plant species inoculated with mycorrhiza might be a potential approach to revegetating mine tailing sites and that H. spectabile is an appropriate plant for phytostabilization of Pb/Zn tailings in northern China due to its higher biomass production and lower metal accumulation in shoots.     

Influence of an arbuscular mycorrhizal fungus on the interaction of a binucleate Rhizoctonia species with Myc+ and Myc- pea roots

A binucleate Rhizoctonia (BNR) species was isolated from a clay loam soil on the Epoisses experimental station of INRA, Dijon and identified as belonging to the anastomosis Group A (AG-A). The BNR was inoculated to a Myc- Pisum sativum mutant (P53, sym30 locus) and its wild-type parent (cv Frisson) in the presence or absence of the arbuscular mycorrhizal fungus Glomus mosseae. The BNR had no significant effect on plant weight. Myc+ and Myc- roots were equally susceptible towards BNR and showed no localized cellular defense responses. The presence of BNR decreased significantly the percentage of root length colonized by G. mosseae and, inversely, G. mosseae reduced the number of BNR monilioid chains formed in root epidermal cells of the two pea genotypes. The pisatin concentration was increased significantly by BNR in both Myc+ and Myc- roots and by G. mosseae in the wild-type pea plants. The highest accumulation of pisatin was observed in Myc+ roots when both fungi were present.     

Effects of symbiosis with Frankia and arbuscular mycorrhizal fungus on the natural abundance of 15N in four species of Casuarina

The effect of interactions between Casuarina species, Frankia strains and AMF on nitrogen isotope fractionation within the plant were determined under conditions where changes in source nitrogen were minimized by growing plants in mineral nitrogen-deficient conditions and without added organic N. Casuarina cunninghamiana, C. equisetifolia, C. glauca, and C. junghuniana were inoculated singly with three Frankia strains or were dual inoculated with Frankia and Glomus fasciculatum. The %N and delta 15N of separated parts of plants inoculated with the three Frankia strains or with Frankia + Glomus were not significantly different within Casuarina species. However, the slow-growing C. junghuniana differed in several variables from the other three species. There was a highly significant, linear relationship between the natural logarithms of cladode N content and delta 15N of plants of the four Casuarina species when inoculated with Frankia or with Frankia + Glomus, showing that nitrogen supply and the correlated variable, plant growth rate, were major determinants of delta 15N. Provision of small quantities of (NH4)2SO4 or KNO3 increased several-fold the growth of three of the Casuarina species when inoculated with Frankia alone or with Frankia + Glomus. Within species, mycorrhizal and non-mycorrhizal plants receiving supplementary soluble phosphate were of similar dry weights at harvest. delta 15N values for cladodes of C. cunninghamiana, C. equisetifolia and C. glauca were similar, but values for the poor growing C. junghuniana were more variable and, with the exception of plants receiving KNO3, were lower than those of the other three species. Reduced growth due to suboptimal availability of N or P had a major influence on delta 15N and, in these conditions where plants could not access significant amounts of organic N, outweighed any effects on cladode delta 15N of colonization by Glomus. delta 15N values of nodules were higher than other parts of Frankia or Frankia + Glomus inoculated Casuarinas, conceivably due to retention in nodules of fixed N, with delta 15N close to zero.     

Density dependent interactions between VA mycorrhizal fungi and even-aged seedlings of two perennial Fabaceae species

Summary The interaction of density and mycorrhizal effects on the growth, mineral nutrition and size distribution of seedlings of two perennial members of the Fabaceae was investigated in pot culture. Seedlings of Otholobium hirtum and Aspalathus linearis were grown at densities of 1, 4, 8 and 16 plants per 13-cm pot with or without vesicular-arbuscular (VA) mycorrhizal inoculum for 120 days. Plant mass, relative growth rates, height and leaf number all decreased with increasing plant density. This was ascribed to the decreasing availability of phosphorus per plant as density increased. O. hirtum was highly dependent on mycorrhizas for P uptake but both mycorrhizal and non-mycorrhizal A. linearis seedlings were able to extract soil P with equal ease. Plant size distribution as measured by the coefficient of variation (CV) of shoot mass was greater at higher densities. CVs of mycorrhizal O. hirtum plants were higher than those of non-mycorrhizal plants. CVs of the facultatively mycorrhizal A. linearis were similar for both mycorrhizal and non-mycorrhizal plants. Higher CVs are attributed to resource preemption by larger individuals. Individuals in populations with high CVs will probably survive stress which would result in the extinction of populations with low CVs. Mass of mycorrhizal plants of both species decreased more rapidly with increasing density than did non-mycorrhizal plant mass. It is concluded that the cost of being mycorrhizal increases as plant density increases, while the benefit decreases. The results suggest that mycorrhizas will influence density-dependent population processes of faculative and obligate mycorrhizal species.     

Parasitic and mutualistic associations between a mycorrhizal fungus and soybean: The effect of phosphorus on host plant-endophyte interactions

Soybean [ Glycine max (L.) Merr. cv. Kent] plants were colonized by the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum (Thaxt. sensu Gerd.) Gerd. and Trappe in pot cultures using an inert medium and a nutrient solution. Phosphorus was provided initially as 0, 25,50, 100 or 200 mg hydroxyapatite [HAP, Ca₁₀(PO₄)₆(OH)₂] per pot. Under the low (0 mg HAP) and high (100 and 200 mg HAP) P regimes, VAM plants showed 20, 25 and 38% growth retardation, respectively, relative to non-colonized controls. At 50 mg HAP, VAM plant growth was significantly enhanced (14%). Dry weight and P content of both VAM and control plants increased with increased P availability throughout the HAP gradient. Intraradical VAM fungal biomass increased linearly with increasing P availability. Extraradical VAM fungal biomass was smaller than the intraradical component of the fungus at the lowest and highest levels of P addition in the growth medium. The ratio of extra- to intraradical mycelium, a suggested index of VAM fungal effectiveness, was greatest for the 50 mg HAP treatment, coinciding with growth enhancement of the host plant. This enhanced growth of the host at an intermediate P level was apparently a result of increased P uptake by the endophyte.     

刺槐接种VA菌根真菌与环境条件的关系

1 引言 国内外众多的试验表明,VA菌根真菌侵染植物根系后,促进植物对养分吸收和物质转化,从而大幅度增加寄主生物量,但也有试验表明,接种VAMF后,寄主生物量并无明显增加,这可能与菌根接种物本身的特点及外界条件有关,其中土壤中磷的含量是重要因素之一。据报道,土壤P过高,对菌根的形成有影响。本文就刺槐接种VAMF,在不同立地环境下寄主生长变化及不同施磷量对VAMF侵染能力、孢子产生量、植株生物量等进行了研究。