Cytological evidence for nucleolar competition in a maize hybrid

We used silver staining to analyze transcnptional activity of nucleolus organizers in maize. The lengths of the silver-stained regions were found to reflect differences in relative nucleolar activity in a translocation line (T6-9a) known to exhibit nucleolar competition. The silver staining technique revealed differential activity between the two nucleolus organizers in 30% of the cells of two inbred lines, B73 and Mo17. In contrast, the hybrid between the two inbreds (B73 Mo 17) exhibited differential activity in 65% of its cells The results indicate that silver staining is a useful tool for assessing the activity of nucleolar organizers in maize. In addition, we found that intracellular nucleolar competition occurs in maize and that the amount of competition increases when the genomes of two inbred lines are combined to form a hybrid.