Nucleolus organizer polymorphism in barley, Hordeum vulgare L.

Abstract

Linde-Laursen, 1. 1984. Nucleolus organizer polymorphism in barley, Hordeum vulgare L. —Hereditas 100:3343. Lund, Sweden. ISSN 0018–0661. Received March 28, 1983 Twenty-nine barley lines with the standard karyotype were differentiated by nucleolus organizer (NOR) polymorphisms. In 27 lines chromosome pair 6 had longer secondary constrictions, larger silver nitrate-stained NORs, and formed larger nucleoli than chromosome pair 7. Two lines showed the opposite combination of chromosomes and characters, but had different sizes and “strengths” of nucleolus organizers on chromosome pair 6. One of these lines had a high frequency of interphase cells with micronucleoli suggesting the presence of an extra pair of nucleolus organizers. The heteromor-phisms of NORs are probably due to tandem duplications. The NORs were located in the secondary constrictions and did not comprise adjacent C-bands. The mean nucleolar volumes were the same in representative lines of the three groups of barley and in a translocation line that has both nucleolar organizers in one chromosome arm and shows “intrachromosomal nucleolar dominance”. This suggests the existence of a compensational mechanism for nucleolus formation. Minor silver nitrate-stained bands sometimes developed at both sides of the centromeres. A positive correlation was indicated between the length of a secondary constriction, the size of a NOR, and the nucleolus formed at it. This may be the normal situation in plants.