RIBOSOMAL RNA CISTRON MULTIPLICITY AND NUCLEOLAR ORGANIZERS IN HEXAPLOID WHEAT

Jag Mohan 1 and Richard B. Flavell 2

1 Epigenetics Research Group, Institute of Animal Genetics, University of Edinburgh EH9 3JN
2 Department of Cytogenetics, Plant Breeding Institute, Trumpington, Cambridge CB2 2LQ

The ribosomal DNA (DNA complementary to ribosomal RNA) content of twelve different wheat genotypes has been studied. Some of these genotypes are aneuploids with deletions or additions of chromosomes bearing nucleolar organisers. The rDNA contents of these genotypes provide several examples of a clear departure from a correlation between the number of rRNA cistrons and the number of nucleolar organisers. Thus the number of rRNA cistrons per nucleolar organiser is not constant in wheat. Wheat DNA was found to have a mean buoyant density of approximately 1.702 g/cc for all genotypes studied and rRNA hybridized selectively to DNA of buoyant density approximately 1.710 g/cc. The thermal stabilities of all the rRNA/DNA hybrids were essentially identical.

Submitted on July 13, 1973
Revised on October 2, 1973