RIBOSOMAL-RNA GENES IN SCOTS PINE (PINUS-SYLVESTRIS L) - CHROMOSOMAL ORGANIZATION AND STRUCTURE

The nuclear 18S, 5.8S and 25S rRNA genes exist as thousands of rDNA re peats in the Scots pine genome. The number and location of rDNA loci ( nucleolus organizers, NORs) were studied by cytological methods, and a restriction map from the coding region of the Scots pine rDNA repeat was constructed using digoxigenin-labeled flax rDNA as a probe. Based on the maximum number of nucleoli and chromosomal secondary constricti ons, Scots pine has at least eight NORs in its haploid genome. The siz e of the Scots pine rDNA repeat unit is approximately 27 kb, two- or t hreefold larger than the typical angiosperm rDNA unit, but similar in size to other characterized conifer rDNA repeats. The intergenic space r region (IGS) of the rDNA repeat unit in Scots pine is longer than 20 kb, and the transcribed spacer regions surrounding the 5.8S gene (ITS 1 and ITS2) span a region of 2.9 kb. Restriction analysis revealed tha t although the coding regions of rDNA repeats are homogeneous, heterog eneity exists in the intergenic spacer region between individuals, as well as among the rDNA repeats within individuals.