The structure and variation of nuclear ribosomal DNA (rDNA) units of
Picea abies, (L.) Karst. was studied by restriction mapping and Southern
hybridization. Conspicuous length variation was found in the internal
transcribed spacer (ITS) region of Picea abies, although the length of
this region is highly conserved both within and among, most of the plant
species. Two types of ITS variants (A and B), displaying a size difference of
0.5 kb in the ITS2 region, were present within individuals of Picea abies
from Sweden, Central Europe and Siberia. A preliminary survey of 14
additional Eurasian and North American species of Picea suggested that
length variation in the ITS region is widespread in this genus. Alltogether
three length variants (A, B and C) were identified. Within individuals of eight
Picea species, two length variants were present within the genome
(combinations of A and B variants in P. glehnii, P. maximowiczii
, P. omorika, P. polita and P. sitchensis and
variants B and C in P. jezoensis, P. likiangensis and P.
spinulosa). Within individuals from five species, however only one rDNA
variant was present in their genome (variant A in P. aurantiaca, P.
engelmannii, P. glauca, P. koraiensis and P. koyamai
; variant B in P. bicolor). The ITS length variation will be useful
as a molecular marker in evolutionary studies 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 interspecific hybridization during the
evolutionary history of Picea.
Key words: Evolution, rDNA, internal transcribed spacers, Picea.
by Alfred E. Szmidt