Structural differentiation of the nucleolus-organizing regions between mitotic and epidermal cells inVicia faba

Abstract

SUMMARY-The nucleolar secondary constrictions of Vicia faba chromosomes were filled with a weakly stained substance when the sections were treated with conventional double staining and examined under an electron microscope. But both silver staining and ribonucleoprotein preferential staining contrasted these constrictions as positively stained areas. On the other hand, the nucleolus-associated chromatin blocks in the epidermal cells were clearly impregnated with silver although they were fully condensed, suggesting that ribosomal (r) RNA genes are organized into the condensed chromosomal segment when cells differentiate into specialized cells such as the epidermal cells.

Cytogenetical Polymorphism of the Nucleolus Organizer Region (Nor s) inAllium CepaL.

“…In interphase, some of the rRNA genes are involved in "Christmas-tree-like transcriptional units", which are major constituents of the dense fibrillar component of the nucleoli while inactive rRNA genes form small pale staining patches called fibrillar centers (FCs) within the dense fibrillar component (12, 9,49,39).…”