Molecular cytogenetic analysis of some Picea species from Eurasia and East Asia

Karyotypes of seven Picea species distributed across Eurasia and East Asia were analyzed using fluorescence in situ hybridization (FISH) and DAPI fluorescent staining. For P. meyeri and P. purpurea, the 5S and 45S rDNA sites were mapped here for the first time, while karyotypes of P. abies, P. obovata, P. schrenkiana, P. crassifolia, and P. omorika were examined from new locations. All the species studied had a similar distribution of 5S rDNA loci on both arms of the large metacentric chromosome III: a more intense signal was observed in the middle of the long arm, partially overlapping with the 45S rDNA signal, and a minor 5S rDNA site was localized terminally on the short arm. The distribution of 5S rDNA loci varied in the karyotypes of the studied species: from 7 to 9 pairs of chromosomes carried 45S rDNA signals of varying intensity. Strong (major) signals were localized intercalarily and coincided with persistent secondary constrictions. Their number per haploid genome was as follows: 8 in P. omorika, 6 in P. abies and P. obovata, and 5 in P. schrenkiana, P. crassifolia, P. purpurea, and P. meyeri. We also detected several minor 45S rDNA sites on the Picea chromosomes that had not been previously described in the literature. Supernumerary (B) chromosomes found in some seedlings of P. obovata, P. meyeri, and P. purpurea did not carry 45S and 5S rDNA loci. Intensely fluorescent DAPI-positive bands were observed in the intercalary regions of the spruce chromosomes, and the centromere regions of certain chromosomes were also stained. Several constant DAPI-positive blocks were identified on chromosomes I, III, and X, with similar locations across all studied species. Fluorescence in situ hybridization with 45S and 5S rDNA probes in combination with DAPI staining allowed us to identify virtually all homologous chromosomes and compare karyotypes of different species. The intra- and interspecific karyotypic diversity in the genus Picea is discussed considering the distribution of 5S and 45S rDNA loci and DAPI signals.