Enzyme maceration, fluorescent staining, and FISH of rDNA of pineapple (Ananas comosus (L.) Merr.) chromosomes

Chromosome analysis of pineapple (Ananas comosus (L.) Merr.), one of the most important tropical fruit trees, was conducted. All experiments were carried out using root tips derived from three cross combinations as plant materials. Good preparations, with all 50 chromosomes relatively extended and well-spread without cytoplasm, were observed under enzyme conditions of "2% Cellulase Onozuka RS and 0.5% Pectolyase Y-23" without pretreatment with 2 mM 8-hydroxyquinoline. CMA-positive (+) bands were observed in telomeric positions of two chromosomes. DAPI-negative bands (-) corresponded with CMA+ bands. The numbers and positions of CMA+ bands were stable. Fluorescence in situ hybridization of rDNA was performed. The 18S-5.8S-25S rDNA sites were detected in telomeric positions of two chromosomes. The 5S rDNA sites were also detected in telomeric positions of two chromosomes. The 5S and 18S-5.8S-25S rDNA sites were located on different chromosomes. The 18S-5.8S-25S rDNA sites corresponded with the CMA+/DAPI- bands. The numbers and positions of rDNA sites were stable.