B chromosomes in Conifers (Study Case of the Genus Picea A. Dietr.)

Abstract

Data on B chromosomes in the genus Picea (Spruce) species are presented. Species of this genus are good objects for studying many problems on the role and origin of supernumerary chromosomes in conifers. Classical methods for studying chromosomes with staining of preparations with acetohematoxylin and the method of fluorescent in situ hybridization (FISH) were used. We report the B chromosomes occurrence in five Picea species and confirmed the data of different authors for seven species. At present, supernumerary chromosomes are found in 23 Picea species including the interspecies hybrid P. × fennica. B chromosomes of Picea species are smaller than A chromosomes; their size (4-6 µm) is 25-30% of the size of A chromosomes. The B chromosomes of spruce species are either meta- or submetacentric, which have been designated as B1 and B2 types respectively. The number of B chromosomes per cell in spruce species varies from one to six. It is generally agreed that B chromosomes are derived from A chromosomes through chromosome arrangements They differ from A chromosomes in sequence composition. The results allow us to consider that B chromosomes are of importance for organisms and possibly may play a role in their adaptation.