Electron microscope autoradiographic studies of RNA metabolism in Trillium erectum microspores

3H-Uridine has been used to investigate the sites of RNA synthesis in the post-meiotic G₁ phase of Trillium microspores using electron microscope autoradiography. The dilute, non-condensed component of the nucleus has been found to be the site of synthesis. When the labelled cells were further incubated in non-radioactive medium the label was found to shift towards the condensed chromatin regions within the nucleus. Two hypotheses to explain the observations are considered, one involving migration of the RNA from the relaxed to condensed regions, the other involving a change in state of the nuclear regions involved in the synthesis. The data are interpreted as favoring the latter possibility.This study supported by grants from the Jane Coffin Childs Memorial Fund for Medical Research and from the Swiss National Fund, Grant Nr. 3202.Fellow of the Jane Coffin Childs Fund for Medical Research.