FLOW CYTOMETRIC PROBING OF CHROMATIN CONDENSATION IN MAIZE DIPLOID NUCLEI

Nuclei were isolated from stems, mesocotyls, nodal roots and root tips of two maize hybrids. The fluorochrome, propidium iodide (PI), was us ed to stain the nuclei that were passed through a flow cytometer-cell sorter. Significant differences in fluorescence intensities were obser ved among the diploid nuclei from the different plant organs. These ob servations, in conjunction with previously reported DAPI fluorescence data, reflect the state of chromatin condensation in diploid nuclei is olated from meristematic and differentiating tissues. Nuclei from root meristematic tissues showed no or very little chromatin condensation. Mesocotyls and nodal roots, 1-wk-old, appeared to contain chromatin i n a more diffuse state owing to completed differentiation which allows more DNA to be accessible to PI. Mesocotyls, 2-wk-old owing to senesc ence, contained degraded chromatin in which DNA was more accessible to PI because it lacked associated proteins. The diploid nuclei from ste ms had the highest amount of chromatin condensation. The results show the usefulness of flow cytometry for analyzing chromatin condensation in plant nuclei. The study also shows the importance of selecting a pa rticular type of fluorochrome in the analysis of nuclear chromatin.