RNA synthesis in roots of Vicia faba

Roots of V. faba were grown in solutions of ³H-cytidine and ³H-uridine, RNA precursors, for 30 min, 1 hr or 2 hr. Grain counts were made over nuclei and cytoplasm in squash preparations. By means of these counts, synthesis of RNA was followed in interphase and dividing cells. Results indicate that:

• 1.1. RNA is synthesized in the nuclei of cells in interphase and early and middle prophase. There appears to be no synthesis in cells in mitosis.
• 2.2. Labeled RNA moves from the nuclei to the cytoplasm.
• 3.3. In late prophase, nuclear RNA is shed into the cytoplasm with the breakdown of the nuclear membrane and nucleolus.
• 4.4. Some grains were seen over the chromosomes. Of the RNA in the nucleus in prophase, very little of it appears to become a chromosome constituent.