Autoradiography of tritiated uridine in shoot apices ofChenopodium rubrum

The incorporation of uridine-5-³H into shoot apices ofChenopodium rubrum, plants was studied using autoradiography. The evaluation of the rate of incorporation into the nucleolus and the extranucleolar part of the nucleus as a function of the total radioactivity in the apex yields quantitative data on the distribution of labeling in these parts of the nucleus. Incubation of intact germinating plants in uridine-³H makes it possible to carry out chase experiments. Curves of uridine incorporation into the nucleolus and the extranucleolar part of the nucleus were obtained which demonstrated a non-linear course of incorporation. When incubating with uridine from 30 to 120 min the nucleolar/extranucleolar ratio of labelling was found to increase from 2 to 3. In chase experiments this ratio changed within three days from 3 to 1. Interpretation of these results in view of the function of RNA localized in different parts of the nucleus is discussed.