TISSUE-SPECIFIC NUCLEAR REPATTERNING IN PLANT-CELLS

Tissue-specific nuclear repatternings, consisting of changes in the nu mber and size of the chromocenters, were observed by analyzing, in Feu lgen squashes and sections, different tissues of several plant species , particularly of lonopsidium savianum. Nuclear repatternings occur ma inly near the base of the meristems. They are due to associations of c hromosomes at their heterochromatic regions. This was confirmed by the results of cytophotometric measurements, showing the same contents of both Feulgen/DNA and heterochromatin in nuclei with a different numbe r of chromocenters. These data also showed that chromosome association does not occur in endoreduplicating or endoreduplicated cells. Autora diographic results after [H-3]thymidine treatments indicated that DNA synthesis does not occur in nuclei with extensive chromosome associati on. A highly significant, positive correlation was found between the n umber of chromocenters in each nucleus and the amount of RNA synthesis as indicated by [H-3]uridine incorporation. It is suggested that chro mosome association plays some role in the regulation of the functional activity of the nucleus and in tissue differentiation.