Uranium uptake and translocation by the arbuscular mycorrhizal fungus, Glomus intraradices, under root‐organ culture conditions

Abstract

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.

Effects of AM colonization on “wild tobacco” plants grown in zinc-contaminated soil

“…Despite this, it has been suggested that AM fungi may eliminate the bioavailability of otherwise toxic contaminants and consequently buffer the soil for plants and other microorganisms (Joner et al 2000). By contrast, Davies et al (2001Davies et al ( , 2002 and Rufyikiri et al (2002Rufyikiri et al ( , 2003 showed, respectively, colonization by G. intraradices enhanced uptake and accumulation of chromium in sunflower and of uranium in cultivated in vitro carrot roots by G. intraradices. Although AM fungi may enhance heavy metal phytoextraction for some plant species, our findings agree with the hypothesis of metal-binding AM fungal capacity as suggested by others (Chen et al 2001, Joner et al 2000, Li & Christie 2000.…”

“…Recent phytoremediation studies that incorporated the AM-variable have had mixed findings. Some studies have shown that AM colonization increases the uptake and accumulation of heavy metals in host plants (Davies et al 2001(Davies et al , 2002Hovsepyan & Greipsson 2004;Rufyikiri et al 2002Rufyikiri et al , 6 2003, while others suggested that AM fungi exude enzymes that participate in the immobilization process of soil contaminants, in which case accumulation in plants is reduced (Joner et al 2000, Weissenhorn et al 1993). …”

Chromium immobilization by extra- and intraradical fungal structures of arbuscular mycorrhizal symbioses

“…At harvest, spore number in RC and HC was assessed by using 1-cm grids marked on the bottom of each petri plate [26]. The roots in RC were collected from the medium by solubilizing the solidified M media with 10 vols of citrate buffer (pH 6.0), and then washed carefully with Milli-Q water and weighed.…”

Impact of arbuscular mycorrhizal fungi on uranium accumulation by plants

“…The first study on the role of an AM fungus on plant U acquisition was performed by Rufyikiri et al (2002). These authors investigated whether the extraradical mycelium of Glomus intraradices (MUCL 41833) could take up U and translocate it towards its host.…”

“…the hyphal compartment, HC) (Rufyikiri et al, 2005). This compartmented in vitro system was preferred by Rufyikiri et al (2002) over bi-compartmented pot systems containing soil because pH of the medium where the extraradical mycelium was developing could be precisely controlled. Indeed, it is known that the pH can play a prevalent role on the process of U uptake because of its effects on the extracellular charges of fungal mycelium (Zhou, 1999;Gadd and White, 1990) and on dominant U species available to the fungal mycelium (Suzuki and Banfield, 1999;Grenthe et al, 1992).…”