Mycorrhization of micropropagated mature wild cherry (Prunus avium L.) and common ash (Fraxinus excelsior L.)

Micropropagated plants of common ash and wild cherry were inoculated with arbuscular mycorrhizal fungi during a 20-day weaning period, after which they were transferred to two different substrata supplemented with slow-release fertilizer. After a 13-week growth period, the stem height and diameter of the ash plants which had been inoculated with Glomus intraradices were three times greater than those of uninoculated control plants. Increasing the peat content of the substratum improved growth of ash. Four weeks after being transferred to pots, shoots of wild cherry inoculated with G. intraradices or G. deserticola were taller and stems thicker than those of control plants, whereas those inoculated with Gigaspora rosea had shorter shoots and thinner stems than the controls. These beneficial effects of fungal inoculation on plant development disappeared after 13 weeks. Increasing the peat content, but not the level of fertiliser of the substratum, improved growth of both inoculated and uninoculated wild cherry

Control by arbuscular endomycorrhizae of Pratylenchus brachyurus in pineapple microplants

Pratylenchus brachyurus (Godfrey) Filip & Schurr-Steekh. has been reported in association with pineapple roots and is considered as an important pathogen on pineapple. Microplants of Queen Tahiti, Smooth Cayenne and Spanish varieties were inoculated with Glomus sp. (LPA21) and/or P. brachyurus at transplanting from axenic conditions or one month later. The presence of the nematode did not affect shoot growth of endomycorrhizal plants. Late P. brachyurus inoculation did not influence growth of nonmycorrhizal plants while early pathogen application caused reductions in nonmycorrhizal plant growth. Nematode number per g of root was significantly decreased for endomycorrhizal plants when pathogen was introduced at outplanting or one month later. Nematode inoculation affected endomycorrhizal colonization estimated by non vital staining for the Queen Tahiti and Spanish varieties but did not alter development of metabolically active arbuscules in roots of the three varieties. P concentration of endomycorrhizal shoots was higher for all treatments and P. brachyurus tended to decrease mineral concentration of nonmycorrhizal plants with early nematode application

Arbuscular mycorrhizal symbiosis elicits shoot proteome changes that are modified during cadmium stress alleviation in Medicago truncatula

Background : Arbuscular mycorrhizal (AM) fungi, which engage a mutualistic symbiosis with the roots of most plant species, have received much attention for their ability to alleviate heavy metal stress in plants, including cadmium (Cd). While the molecular bases of Cd tolerance displayed by mycorrhizal plants have been extensively analysed in roots, very little is known regarding the mechanisms by which legume aboveground organs can escape metal toxicity upon AM symbiosis. As a model system to address this question, we used Glomus irregulare-colonised Medicago truncatula plants, which were previously shown to accumulate and tolerate heavy metal in their shoots when grown in a substrate spiked with 2 mg Cd kg-1.[br/] Results : The measurement of three indicators for metal phytoextraction showed that shoots of mycorrhizal M. truncatula plants have a capacity for extracting Cd that is not related to an increase in root-to-shoot translocation rate, but to a high level of allocation plasticity. When analysing the photosynthetic performance in metal-treated mycorrhizal plants relative to those only Cd-supplied, it turned out that the presence of G. irregulare partially alleviated the negative effects of Cd on photosynthesis. To test the mechanisms by which shoots of Cd-treated mycorrhizal plants avoid metal toxicity, we performed a 2-DE/MALDI/TOF-based comparative proteomic analysis of the M. truncatula shoot responses upon mycorrhization and Cd exposure. Whereas the metalresponsive shoot proteins currently identified in non-mycorrhizal M. truncatula indicated that Cd impaired CO2 assimilation, the mycorrhiza-responsive shoot proteome was characterised by an increase in photosynthesisrelated proteins coupled to a reduction in glugoneogenesis/glycolysis and antioxidant processes. By contrast, Cd was found to trigger the opposite response coupled the up-accumulation of molecular chaperones in shoot of mycorrhizal plants relative to those metal-free.[br/] Conclusion : Besides drawing a first picture of shoot proteome modifications upon AM symbiosis and/or heavy metal stress in legume plants, the current work argues for allocation plasticity as the main driving force for Cd extraction in aboveground tissues of M. truncatula upon mycorrhization. Additionally, according to the retrieved proteomic data, we propose that shoots of mycorrhizal legume plants escape Cd toxicity through a metabolic shift implying the glycolysis-mediated mobilization of defence mechanisms at the expense of the photosynthesis-dependent symbiotic sucrose sink

Pathogenesis-related proteins in roots: a role in plant resistance or an epiphenomenon?

International audienceAlthough Pathogenesis-Related (PR) proteins have been identified in numerous monocotyledons and dicotyledons across different genera and in relation to very different physiological situations, relatively few studies have been conducted on roots which are the site of multimicrobial interactions. PR proteins are considered to be inducible proteins elicited by many environmental and developmental stimuli, but an increasing body of data points to their occurrence as constitutive components in different plant organs (Edreva 2005), including roots. This is the case, for example, of a Nicotiana glutinosa x Nicotiana debney hybrid which over-expresses PR protein genes and shows constitutive resistance to root fungal pathogens, but susceptibility to root colonisation by symbiotic fungi. However, successful root colonisation by beneficial microbes must imply a permanent control over microbial development. This could result from defence mechanisms being modulated in their intensity by the beneficial microbe (Gianinazzi 1981). In mycorrhizal interactions this phenomenon is associated with the weak and localized expression of several PR protein genes, and it could be responsible for priming the localized and systemic resistance against subsequent attack by microbial pathogens that is induced in mycorrhizal root systems. The induction of resistance by mycorrhiza formation requires a yet undefined systemic signal in roots, the activity of which in the above-ground part of the plant is not clear. Moreover, PRprotein synthesis induced by fungal pathogens in roots is associated with the development of root disease which raises the question of the role of PR proteins in root control over microbial invasion (Dumas-Gaudot et al. 2000). Edreva A, 2005, Gen.Plant Physiology, 31,105-124 Gianinazzi S, 1981, Agric.Ecosys.Environ.35, 105-112 Dumas-Gaudot E et al., 2000, Arbuscular mycorrhizas: physiology and function, 173-200

Bioalternatives to chemicals in plant production and in cleaning up the environment: hopes and reality

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Mycorrhizal biotechnology in plant management

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Analysis of the molecular language and gene expression in VA endomycorrhizal symbiosis, an approach toward selective host plant management of fungal infection

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Influence of intergeneric grafts between host and non-host legumes on formation of vesicular-arbuscular mycorrhiza

Stem grafts were carried out between different varieties of vesicular‐arbuscular (VA) mycorrhizal host (pea, soybean) and non‐host (lupin) legumes. Only grafts on host rootstock were successful. Self‐grafts of three pea varieties (Amino, Solara, Frisson), and interspecific grafts between soybean (var. Amsoy 71) and pea (var. Frisson), did not generally affect development of, or arbuscule formation by, Glomus intraradices Schenck & Smith or G. mosseae Nicol. & Gerd. within the rootstock. In contrast, lupin (var. Alban and Lucky) scions greatly reduced colonization of the root cortex and completely inhibited arbuscule formation by both fungi in grafted pea rootstock. The possible role of mobile shoot factors in non‐host resistance to VA mycorrhizal fungi in lupins is discussed

Quest for useful genes to enhance mycorrhizal benefits benefits to crop plants

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Morphological integration and functional compatibility between symbionts in vesicular arbuscular endomycorrhizal associations

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