Comparison of U-233 and P-33 uptake and translocation by the arbuscular mycorrhizal fungus Glomus intraradices in root organ culture conditions

This study aimed to quantify and compare U-233 and P-33 uptake and translocation by hyphae of the arbuscular mycorrhizal (AM) fungus Glomus intraradices in root organ culture conditions with transformed carrot (Daucus carota L.) roots as host. Mycorrhizal roots were grown in two-compartment Petri dishes to spatially separate a root compartment (RC) and a hyphal compartment (HC). The HC was labelled with 8.33 Bq U-233 ml(-1) and 13.33 Bq P-33 ml(-1). After 2 weeks contact between hyphae and the labelled solution, U-233 and P-33 activities were measured in the RC and in the HC. U-233 and P-33 were taken up by the extraradical AM mycelium grown in the HC and this uptake represented 4.4% and 16% of the initial isotope supply, respectively. The translocation into roots developing in the RC via hyphae accounted for 5.9% and 72% of the initial isotope supply, respectively. Thus, both uptake and translocation were much higher for P-33 than for U-233. This suggests (1) the existence in hyphal tissues of efficient mechanisms limiting the uptake and translocation of non-essential elements such as U, and (2) that the hyphae have a higher sequestration than translocation function for U, and the converse for P