Nucleolar component behaviour in plant cells under different physiological conditions. A morphological, cytochemical and quantitative study

Different nucleolar components of Allium cepa L. root meristem cells under physiological conditions of proliferation and quiescence were quantitatively analyzed after the application of morphometric and cytochemical techniques. Our data show that quiescent cells have a diminished nucleolar size when compared with proliferating cells. However, the silver stained area in relation to the nucleolar area (fibrillar component) is maintained constant in both physiological conditions. We also detected a smaller number of vacuoles per nucleolar volume unit in the case of low transcriptional activity. Cytochemical results obtained in both physiological conditions allowed us to postulate about the distribution of the acidic nucleolar proteins responsible for the NOR‐silver staining.