Polyploid Genome Structure of Drosera spatulata Complex (Droseraceae)

To infer genome structures and chromosome differentiations with karyomorphological changing among these 3 Drosera species, we applied base-specific fluorescent staining with GC-rich specific chromomycin A3 (CMA) and AT-rich specific 4′,6-diamidino-2-phenylindole (DAPI), fluorescent in situ hybridization (FISH) with 45S rDNA, and genomic in situ hybridization (GISH) with 2 parental genomic probes of D. rotundifolia (2n=20) and D. spatulata (2n=40) to somatic metaphase chromosomes of D. tokaiensis (2n=60). The chromosome ploidies in somatic cells were diploid in D. rotundifolia, tetraploid in D. spatulata, and hexaploid in D. tokaiensis. All 20 chromosomes of D. rotundifolia were middle size, while all 40 chromosomes of D. spatulata were small size. Drosera tokaiensis showed a bimodal karyotype which had 20 middle-sized chromosomes and 40 small-sized chromosomes. In base-specific fluorescent staining, satellites stained with CMA positive and DAPI negative were observed at one end of 1 pair of small sized chromosomes in D. spatulata and D. tokaiensis, but not in D. rotundifolia. The FISH results showed that the 45S rDNA signals of all species were located at chromosome ends or satellites. Two major signals for the 45S rDNAs were observed in D. rotundifolia, while 2 major signals and 2 minor signals were detected in both D. spatulata and D. tokaiensis. Dual simultaneous GISH showed the sufficient demonstration to discriminate parental genomes in D. tokaiensis.