Aneusomaty and polysomaty in Cymodocea nodosa (Ucria) Ascherson from Mediterranean Sea (Sicily, Italy)

Basic cytogenetic knowledge and genome size data on marine phanerogams are essentially limited, although they are indispensable to plan correct experimental designs and for the right interpretation of genetic data, particularly those requiring detailed analyses of genome structure and evolution. Observations on mitotic divisions and chromosomal behaviours as well as DNA measurements have been carried out on five Cymodocea nodosa populations from Sicilian coasts. Standard chromosome counting and Image Cytometric analyses were used to determine the chromosome number and the ploidy of each population. High chromosome number variation was detected in individuals from all the studied populations, even in a single root (aneusomaty). The numbers varied according to the cell position. Near the apical meristem, it was lower, while far from the apex the majority of dividing cells showed higher chromosome numbers. Mitotic anomalies were also detected. The relative DNA value of nuclei confirmed that all of the studied populations presented polysomaty. Cytological and cytometric data clearly indicated that the combined action of endopolyploidy and mitotic anomalies were involved in this uncommon cytogenetic behavior. The data reported represent the first contribution to understanding the basic cytogenetics in this genus.