Ag-NOR proteins and rDNA transcriptional activity in plant cells

In this work we used Allium cepa root meristem cells in actively growing conditions and under treatment with the protein synthesis inhibitors cycloheximide (CHM) and puromycin. Morphological and quantitative results indicate that these drugs induce dramatic alterations in nucleolar structure reflected by a decrease of nucleolar size, much more evident under treatment with CHM, and by segregation of its main components. Quantitative analysis shows a decrease in NOR-silver staining after treatment with CHM, whereas in cells treated with puromycin NOR-silver staining remains constant. Our results reveal a decrease in the Ag-NOR proteins under conditions of diminished cell activity, suggesting a direct relationship between the quantity of Ag-NOR proteins and transcriptional activity. Using two-dimensional gel electrophoresis and NOR-silver staining in gels, we have characterized some proteins corresponding to molecular weights of 28 and 31 KD and pI of approximately 5.2. After treatment with CHM, reactivity of these proteins against NOR-silver staining is diminished. By means of a morphological study, analysis of NOR-silver staining, and of anti-DNA and RNAse-gold labeling, we have tried an approach to the nucleolar organization in plant cells. Our results suggest that the fibrillar component shows a reticular distribution where fibrillar centers, as described in animal cells, are not distinguished.