Nucleoli, rRNA genes and ITS region in Posidonia oceanica (L.) Delile

The maximum number of nucleoli was counted in interphase nuclei of Posidoni a oceanica, and a restriction pattern of nuclear rDNA was obtained after di gestion with four restriction endonucleases and Southern hybridization. P. oceanica has only one type of ribosomal gene whose size was estimated to be 18.5 kbp long. The nucleotide sequence of the entire ITS region was also d etermined by direct sequencing of PCR amplified DNA fragments. The sequence of the ITS region was aligned with those of homologous regions of other mo nocots available in literature, and phylogenetic trees were obtained.