Summary• Uranium (U) uptake and translocation by the arbuscular mycorrhizal (AM) fungus Glomus intraradices were studied under root-organ culture conditions with Agrobacterium rhizogenes -transformed carrot ( Daucus carota ) roots as host.• Two-compartment Petri plates were used to spatially separate a root compartment (RC) and a hyphal compartment (HC); root growth was restricted to the RC while extraradical hyphae grew in both RC and HC. The HC was labelled with 0.1 µM 233 U at different pH conditions. At the end of the experiment, U was measured in the RC and in the HC.• The U absorption by the AM fungus was observed. It included; U uptake by the mycelium developing in the HC, and U translocation from the HC to the RC. The magnitude of this uptake and translocation was highly influenced by the pH of the growth medium, while translocation was highly correlated with the number of hyphae crossing the partition separating the two compartments.• These results are the first to show that an AM fungus can take up and translocate U towards roots.

Summary• Here, the respective contributions of the arbuscular mycorrhizal (AM) fungus Glomus intraradices and carrot ( Daucus carota ) roots to the uptake and translocation of uranium (U) were quantified and compared.• The U absorption by the AM fungus and roots was observed by growing mycorrhizal and nonmycorrhizal roots in two-compartment Petri plates. The central compartment allowed growth of roots and extraradical fungal hyphae. The external compartment (EC), which was labelled with 0.1 µ M 233 U, allowed growth of: hyphae only (hyphal compartment, HC), both mycorrhizal roots and hyphae (root hyphal compartment, RHC), or nonmycorrhizal roots (root compartment, RC).• The U concentration was 5.5 and 9.6 times higher for hyphae than for the mycorrhizal and nonmycorrhizal roots, respectively, both developing in the EC's. Translocation of U was similar for the RHC and the HC systems, and was 8 times higher for these two systems than for the RC system.• These results indicate that the U flux rate was higher in fungal hyphae than in roots, while the intraradical hyphae may significantly contribute to the U immobilization by mycorrhizal roots.

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Some mycorrhizal plants exhibit greater resistance than nonmycorrhizal plants to aluminium toxicity. This has not yet been shown for banana despite its importance as a cash and food crop in tropical regions, although bananas are sensitive to aluminium stress. We studied the effects of the arbuscular mycorrhizal fungus Glomus intraradices in alleviating aluminium toxicity in the banana cultivar Grande Naine grown in a continuous-nutrient-flow cultivation system using dilute solution. The micropropagated plants, some of which were inoculated with arbuscular mycorrhizal fungus, were grown for 40 d in pots filled with sand, and continuously irrigated with a nutrient solution containing up to 180 µM of aluminium. Water and nutrient uptake were measured once a week for 24 h, and root arbuscular mycorrhizal fungal colonization, biomass production, and mineral content of roots and shoots were measured at harvest. The root arbuscular mycorrhizal fungal colonization was large, and not significantly influenced by aluminium treatment. The effects of aluminium on both mycorrhizal and nonmycorrhizal plants were : decrease in biomass production, water and nutrient uptake, and magnesium content of roots and shoots ; greater aluminium content in roots than in shoots ; and increase in potassium and phosphorus content, particularly in roots. A significant positive effect of arbuscular mycorrhizal fungi on plant growth was observed with aluminium treatment, and was most pronounced at the highest concentration. The benefits, compared with nonmycorrhizal plants, included : increase in shoot dry weight, uptake of water and of most nutrients, and in calcium, magnesium and phosphorus content, particularly in roots ; decrease in aluminium content in root and shoot ; and delay in the appearance of aluminium-induced leaf symptoms. These results indicate that arbuscular mycorrhizal fungi could be effective in alleviating aluminium toxicity to banana plants.

This review summarizes current knowledge on the contribution of mycorrhizal fungi to radiocesium immobilization and plant accumulation. These root symbionts develop extended hyphae in soils and readily contribute to the soil-to-plant transfer of some nutrients. Available data show that ecto-mycorrhizal (ECM) fungi can accumulate high concentration of radiocesium in their extraradical phase while radiocesium uptake and accumulation by arbuscular mycorrhizal (AM) fungi is limited. Yet, both ECM and AM fungi can transport radiocesium to their host plants, but this transport is low. In addition, mycorrhizal fungi could thus either store radiocesium in their intraradical phase or limit its root-to-shoot translocation. The review discusses the impact of soil characteristics, and fungal and plant transporters on radiocesium uptake and accumulation in plants, as well as the potential role of mycorrhizal fungi in phytoremediation strategies.

The interaction between four arbuscular mycorrhizal (AM) fungi, Glomus sp., G. proliferum , G. intraradices and G. versiforme , and the root-rot fungus Cylindrocladium spathiphylli , and subsequent effects on growth and phosphorus nutrition of banana ( Musa acuminata , AAA, cv. Grande Naine) were investigated under glasshouse conditions. Overall, root infection by C. spathiphylli reduced the growth of banana plants, but preinoculation with AM fungi significantly attenuated this detrimental effect. Lower disease severity, stimulation of growth and increase of shoot P content were observed for the plants inoculated with one of the four AM fungi. Glomus sp. and G. proliferum induced the largest increase in growth parameters and shoot P content as compared to G. intraradices and G. versiforme , in the presence as well as in the absence of C. spathiphylli . Root damage caused by C. spathiphylli was decreased in the presence of AM fungi, but the inoculation of mycorrhizal plants with C. spathiphylli also decreased the intensity of AM fungal root colonization, indicating a clear interaction between the two organisms.

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