Analisi del cariotipo e livelli di ploidia in fanerogame marine del Mar Mediterraneo

Cytogenetic studies for systematic and evolutionary purposes are lacking on marine phanerogams. In this study was reported for the first time the karyotype features and genome size of Cymodocea nodosa (Ucria) Ascherson, Halophila stipulacea (Forsskål) Ascherson, Posidonia oceanica (L.) Delile e Zostera noltei Hornemann populations from different Sicilian localities. Squash method / Azur-A staining for chromosome counting and Image Cytometric (IC) analyses were used to determine the chromosome number and the ploidy of each species. Also, was applied flow-cytometric (FC) genome size measurement and fluorescence in situ hybridization (FISH) for localization of telomere and ribosomal DNA (rDNA) using super-resolution microscopy. The estimated 2C-value was 12.26 ± 0.2 pg for H. stipulacea (2n = 18), 1.35 ± 0.02 pg DNA for Z. noltei (2n = 12), 6.88 ± 0.02 pg for P. oceanica (2n = 20) and 0.85 ± 01 pg (FC) and 1.43 ± 0.01 pg (IC) for C. nodosa (2n = 8), using Pisum sativum L. "Ctirad" (2C-value = 9.05 pg), Raphanus sativus "Voran" (1.11 pg), Glycine max (L.) Merr. convar. max var. max (2.21 pg) and Pisum sativum cv. “Viktoria, Kifejtö Borsó” (9.09 pg) as the calibration standard, respectively. The presence of somatic polyploidy has been highlighted in all species studied, but the mechanisms involved seem to be different. This could explain the typical chromosomal number 2n = 18, 2n = 20, 2n = 12 in all cell lines of H. stipulacea, P. oceanica and Z. noltei, respectively. Furthermore, the presence of aneusomatia correlated to mitotic anomalies was found in C. nodosa. The existence of these phenomena clarifies the presence of different cytotypes in a single individual (even in a single root) and allows us to establish that the correct chromosomal number for this species is 2n = 8. The relative DNA value of the nuclei and the number and position of telomeric sites and 45S rDNA loci confirms the presence of polysomaty. These data show the variability of rDNA within the cytotypes of C. nodosa, provide anchor points for (comparative) genetic maps and could be important for studies on the evolution of the karyotype. The data reported represent the first contribution to understanding the basic cytogenetics and a first step to unravel karyotype evolution among seagrasses.