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Radiocaesium enters the food chain when plants absorb it from soil, in a process that is strongly dependent on soil properties and plant and microbial species. Among the microbial species, arbuscular mycorrhizal (AM) fungi are obligate symbionts that colonize the root cortex of many plants and develop an extraradical mycelial (ERM) network that ramifies in the soil. Despite the well-known involvement of this ERM network in mineral nutrition and uptake of some heavy metals, only limited data are available on its role in radiocaesium transport in plants. We used root-organ culture to demonstrate that the ERM of the AM fungus Glomus lamellosum can take up, possibly accumulate and unambiguously translocate radiocaesium from a 137Cs-labelled synthetic root-free compartment to a root compartment and within the roots. The accumulation of 137Cs by hyphae in the root-free compartment may be explained by sequestration in the hyphae or by a bottleneck effect resulting from a limited number of hyphae crossing the partition between the two compartments. Uptake and translocation resulted from the incorporation of 137Cs into the fungal hyphae, as no 137Cs was detected in mycorrhizal roots treated with formaldehyde. The importance of the translocation process was indicated by the correlation between 137Cs measured in the roots and the total hyphal length connecting the roots with the labelled compartment. 137Cs may be translocated via a tubular vacuolar system or by cytoplasmic streaming per se.

Vegetative compatibility and amplified fragment length polymorphism (AFLP) genotyping of in vitro multispores clonal lineages, issued from the same ancestor culture of the arbuscular mycorrhizal fungal strain MUCL 43194 and subcultured several generations in different locations, was assessed. Vegetative compatibility was studied by confronting the germ tubes of two spores from the same or different clonal lineages and stained with nitrotetrazolium blue-Trypan blue and diamidinophenylindole to detect hyphal fusions and nuclei, respectively. Further AFLP analysis of single spores was performed to assess the genetic profile and Dice similarity between clonal lineages. Germ tubes of spores distant by as many as 69 generations were capable of fusing. The anastomosis frequencies averaged 69% between spores from the same clonal lineage, 57% between spores from different clonal lineages, and 0% between spores belonging to different strains. The AFLP patterns showed similarities averaging 92% within clonal lineages and 86% between clonal lineages. Each spore presented unique genotype and some of them shared more markers with spores from different lineages than within the same lineage. We showed that MUCL 43194 maintained self-recognition for long periods of subcultures in vitro and that spores involved in compatibility tests had different genotypes. Our findings suggest that MUCL 43194 maintains genetic diversity by means of anastomoses.