Cytochemical and ultrastructural studies of changes in the nucleus and nucleolus during cell differentiation in the root cortex of Haemanthus katharinae.

Dimensions,dry mass content, binding of [3H]actinomycin D ([3H]AMD), and [3H]uridine incorporation in the nuclei and nucleoli as well as their ultrastructure during growth and differentiation of the root cortex cells of Haemanthus katharinae were compared. The dry mass of the nuclei did not change, the condensed chromatin content was slightly augmented, and the ability of the nuclei to bind [3H]AMD became somewhat decreased, whereas a considerable reduction was observed in the [3H]uridine incorporation. The highest capability for the binding of [3H]AMD and the highest intensity of RNA synthesis were demonstrated by nuclei in the meristematic zone and during the most intensive cell growth. The size of the nucleoli, their dry mass, the amount of granular component, and the intensity of [3H]uridine incorporation underwent a steady decrease as the cells grew and differentiated. The progressing differentiation of the cells was accompanied by an increasing participation of arginine-rich histones in restraining the capacity for [3H]AMD binding.