Differential staining and in situ hybridization of nucleolar organizers and centromeres in Cycas revoluta chromosomes

Nucleolar organizers (NORs) and centromeres in the somatic metaphase chromosomes (2n = 22) of Cycas revoluta Thunb. were differentially stained by silver staining and Cd-staining. Silver deposits (Ag-NORs) were located at the terminal end of the long arm of four submetacentric chromosomes and nine telocentric chromosomes. The maximum number of nucleoli per nucleus was 13. In situ hybridization with biotin-labeled rDNA revealed that rRNA genes were located at the terminal ends of four submetacentric chromosomes and all 12 telocentric chromosomes. Most of the signals of rDNA coincided to Ag-NORs. Differential staining with the DNA base specific fluorochromes indicated that the NORs were GC-rich and the centromeres were AT-rich. The proximal and terminal regions of the telocentric chromosomes were GC-rich. A few interstitial GC- and AT-rich bands were observed in some chromosomes.