The Nucleolus Organizer Region of Maize (ZEA MAYS L.): Tests for Ribosomal Gene Compensation or Magnification.
Ribosomal gene compensation and magnification that might be detected on a whole-plant basis was not found in maize. Plants monosomic for chromosome 6 (the NOR chromosome) were compared with monosomic-8 and monosomic-10 plants, disomic sibs, and parental lines. Assuming no rDNA compensation, monosomic-6 plants showed approximately the decrease expected in rRNA cistron number. Monosomic-8 had a normal ribosomal gene number, while monosomic-10 showed a decrease; but further documentation is needed. Besides demonstrating the absence of gene compensation, the results document our previous conclusion that maize chromosome 6 carries DNA complementary to ribosomal RNA. Further documentation was provided from studies with trisomic chromosome 6 plants showing proportional increases in ribosomal gene number. Progeny of the monosomic plants crossed as males to a standard singlecross hybrid possessed expected ribosomal gene numbers suggesting the lack of ribosomal gene magnification.-The ragged (rgd) mutant of maize, suspected of being deficient in rRNA cistrons, had a normal number.
Phillips
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RL
Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, Minnesota 55101 Department of Biological Sciences, Illinois State University, Normal, Illinois 61761.
Weber
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DF
Kleese
R A
RA
Wang
S S
SS