Contribution of hyphae and roots to uranium uptake and translocation by arbuscular mycorrhizal carrot roots under root‐organ culture conditions

Abstract

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.

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

“…Notably, the lowest percent Zn extracted was found in the AM roots at 250-[Zn], corresponding to the highest level of root colonization. These same trends can also be extrapolated from other phytoremediation studies (Davies et al 2001, Joner & Leyval 1997, Rufyikiri et al 2003, Wenger et al 2000. Based on our Zn removal yield results, additional studies are needed to assess the effectiveness of phytoextraction in soil remediation processes.…”

“…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.…”

“…The increase in AM root colonization is likely the result of numerous factors including increases in soil-Zn concentration and the subsequent decrease in soil pH. Rufyikiri et al (2003), who assessed root-and hypha-induced substrate-pH modifications, suggested that roots lead to an acidification while mycelium to an alkalinization of the growth medium. This phenomenon may explain the significantly more acidic soil pH in non-AM than AM treatments at 250- [Zn].…”

“…This phenomenon may explain the significantly more acidic soil pH in non-AM than AM treatments at 250- [Zn]. Yet, the differences in soil pH could also be attributed to the metal-binding capacity of AM fungi despite some active pH modification by the hyphal exudates (Rufyikiri et al 2003). Phosphorus-Zn interactions may also have contributed to the antagonistic; yet, no differences were found between AM and non-AM treatments to suggested a significant interaction.…”

Impact of arbuscular mycorrhizal fungi on uranium accumulation by plants

“…Indeed, at higher pH, and especially at pH 8, the major U species in solution were neutral or negatively charged. Nonetheless, at pH 5.5, Rufyikiri et al (2003) observed that Cu-extractable U represented 15% of the U content of the fungal mycelium, and that further extraction with HCl desorbed 67% of U (200 mg fresh roots and 20 mg fresh extraradical mycelium were equilibrated for 3 h with 15 ml and 5 ml of a solution containing 10 À2 M CuSO 4 and then with 10 À1 M HCl). Finally, possible adsorption of U on intracellular membranes is also to be excluded as cytoplasmic pH was probably near neutral and vesicular or vacuolar pH is slightly acidic (Rasmussen et al, 2000;Saito et al, 2004).…”