LENGTH VARIATION IN THE INTERNAL TRANSCRIBED SPACERS OF RIBOSOMAL DNAIN PICEA-ABIES AND RELATED SPECIES

The structure and variation of nuclear ribosomal DNA (rDNA) units of P icea abies, (L.) Karst. was studied by restriction mapping and Souther n hybridization. Conspicuous length variation was found in the interna l transcribed spacer (ITS) region of P. abies, although the length of this region is highly conserved both within and among most of the plan t species. Two types of ITS variants (A and B), displaying a size diff erence of 0.5 kb in the ITS2 region, were present within individuals o f P. abies from Sweden, Central Europe and Siberia. A preliminary surv ey of 14 additional Eurasian and North American species of Picea sugge sted that length variation in the ITS region is widespread in this gen us. All together three length variants (A, B and C) were identified. W ithin individuals of eight Picea species, two length variants were pre sent within the genome (combinations of A and B variants in P. glehnii , P. maximowiczii, P. omorika, P. polita and P. sitchensis and variant s B and C in P. jezoensis, P. likiangensis and P. spinulosa). Within i ndividuals from five species, however only one rDNA variant was presen t in their genome (variant A in P. aurantiaca, P. engelmannii, P. glau ca, P. koraiensis and P. koyamai; variant B in P. bicolor). The ITS le ngth variation will be useful as a molecular marker in evolutionary st udies of the Picea species complex, whose phylogeny is controversial. The presence of intraindividual variation in, and shared polymorphism of the, ITS length variants raises questions about the occurrence of i nterspecific hybridization during the evolutionary history of Picea.