Correlation of structure and RNA synthesis in the nucleolus-organizing polytene chromosomes of Phaseolus vulgaris

The relationship between RNA synthesis and morphology of the nucleolus-organizing polytene chromosomes in the highly endopolyploid suspensor cells of Phaseolus vulgaris has been studied by actinomycin D treatment, temperature lowering, and H³-uridine autoradiography. Actinomycin D and low temperature induce a condensation of the giant chromosomes, particularly of the nuoleolus organizers and of the intranucleolar regions of the chromosomes. RNA synthesis occurs in the extended state of the chromosomes, but it ceases in the highly condensed state caused by the treatment of the cells either with actinomycin D or with low temperature.