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 of mercury contamination. With the aim to study genotoxic effect of mercury on this plant species, we analyzed genomic DNA of plants treated with 1 µM mercury for 15 days in aquarium. At the end of this treatment, plants accumulated elevated mercury concentrations in their leaves. After ultracentrifugation in a Cs 2 SO 4 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-blot- ting and hybridization with these variable DNA families, labelled with digoxi- genin, indicated that these DNA sequences are at least partially lost in mercury treated plants. It was determined, by genomic DNA slot-blotting and hy- bridization, that DNA loss of A-T rich DNA sequences (forming the light shoulder) was around 48%.