Pollen Tube Growth and Ribonucleic Acid Synthesis by Vegetative and Generative Nuclei of Tradescantia

Uridine–H 3 is incorporated into both the vegetative (tube) nucleus and the generative nucleus of Tradescantia paludosa within 15 min after transfer of pollen to the growth medium. This incorporation is sensitive to actinomycin‐D. In the presence of actinomycin‐D in the medium at concentrations high enough to inhibit all RNA synthesis, germination, early pollen tube elongation, and the movement of the two nuclei from the pollen grain into the tube does not seem to be inhibited. Actinomycin‐D inhibits later tube elongation and generative‐nucleus division. From these results it is concluded that the vegetative nucleus is biochemically functional at least during the early period of tube growth and is not a degenerate structure. It seems logical also to assume that the messenger‐RNAs required for early tube elongation and nuclear migration are of the long‐lived type, and that both the messenger‐RNA and the ribosomal‐RNA required for these processes is synthesized in the pollen grain prior to anther dehiscence.