Size variation of chromomycin A₃-band in chromosomes of Douglas fir, Pseudotsuga menziesii

Abstract

Somatic chromosomes of 307 seedlings of Pseudotsuga menziesii (Mirb.) Franco var. menziesii from four native localities in Canada and 203 seedlings of P. menziesii var. glauca (Beissn) Franco from two localities in U.S.A. were stained with guanine-specific chromomycin A₃ (CMA). The chromosome complements (2n=26) of the two varieties were commonly composed of ten metacentric, 12 submetacentric and four telocentric chromosomes. Six thick CMA-bands appeared in the interstitial region of a pair of metacentric chromosomes and in the proximal regions of the long arms of two pairs of submetacentric chromosomes. However, the CMA-bands varied in size among the members of the populations. The large CMA-bands of the submetacentric chromosome were observed more frequently in var. glauca than in var. menziesii. Frequency of each sized CMA-band varied within the populations or the varieties. Bright CMA-blocks were associated to nucleoli in the interphase nucleus and the CMA-bands were coincided in location with the secondary constrictions. Ribosomal DNA hybridized in situ to the thick CMA-band regions.