Multiple locations of the rRNA genes in chromosomes of pines, Pinus densiflora and P. thunbergii

The ribosomal RNA (rRNA) genes were mapped on somatic chromosomes of Japanese red pine (Pinus densiflora) and Japanese black pine (P. thunbergii) by in situ hybridization using biotin-labeled 18S-25S rDNA. Cytochemical detection of the hybridized probe showed many signals in the interphase nuclei and, prophase and metaphase chromosomes in both species. In the metaphase complement of P. densiflora, the signals appeared singly at the interstitial region of seven pairs of the chromosomes. In P. thunbergii, ten strong and two weak signals appeared at the interstitial region of six pairs of the chromosomes. The hybridization sites coincided with the interstitial chromomycin A3-bands or secondary constricted regions.