RNA synthesis and changes in template--DNA activity during the growth and differentiation of parenchyma cells of the primary cortex of roots of Zea mays and Tulipa kaufmanniana.

In this study, changes in DNA transcription activity are presented during parenchymal cell differentiation of the primary cortex of roots of a species with elevated DNA content in which endomitotic polyploidization does not occur (Tulipa kaufmanniana), as well as a species with low content levels in which an increase in endomitotic polyploidization occurs during differentiation (Zea mays). Changes in the degree of histone acetylation during the cellular differentiation of both species were also studied. An autoradiographic method was employed using the following indicators: for transcription activity--3H-uridine; for potential activity of template DNA--3H-actinomycin D (3H-AMD); for histone acetylation--the intensity of labelled nuclei after incubation with 3H-sodium acetate, as well as decrease in nuclei radioactivity after extraction of the histone fractions. It was found that during cellular growth and differentiation in both Zea mays and Tulipa daufmanniana (and therefore, irrespective of the presence or absence of endomitotic polyploidization) a progressive decrease of DNA transcription activity occurs. At the same time, the possibility that the acetylation of arginine--rich histones plays a definite, yet undecisive, role in the regulation of DNA transcription activity cannot be excluded.