Mercury-induced DNA variations in the genome of Posidonia oceanica Delile

Posidonia oceanica Delile is a marine phanerogam, largely spread in the Mediterranean basin, where forms large prairies. Since this plant can live on mercury rich sites, this species is used as a biological indicator or mercury contamination. With the aim to study genotoxic effect of mercury on this plant species, we analyzed genomic DNA of plants treated with 1 uM mercury for 15 days in aquarium. At the end of this treatment, plants accumulated elevated mercury concentrations in their leaves. After ultracentrifugation in a Cs2SO4 gradient, P. oceanica genomic DNA profile showed, beside the main peak, a light shoulder containing A-T rich DNA sequences. This shoulder is missing in the profile of DNA isolated from mercury treated plants. Gradient slot-blotting and hybridization with these variable DNA families, labelled with digoxigenin, indicated that thes DNA sequences are at least partially lost in mercury treated plants. It was determined, by genomic DNA slot-blotting and hybridization, that DNA loss of A-T rich DNA sequences (forming the light shoulder) was around 48%.