ONSET OF CELLULAR SYNTHETIC ACTIVITY IN ROOTS OF GERMINATING CORN

The onset of cellular synthetic activities in roots of the germinating corn embryo was studied by autoradiographic techniques. It was found that thymidine is exclusively incorporated in the cytoplasm during the first 33 h of germination. Later, thymidine is also incorporated into the nuclei. Digestion controls show that the incorporated thymidine-both cytoplasmic and nuclear-is in DNA. Combining a pulse of 3H-thymidine and a long chase it was found that thymidine which was incorporated exclusively into cytoplasmic DNA at the beginning of the chasing" period is also incorporated into nuclear DNA at the end of this period. This and other results suggest that there is a moving of the cytoplasm-incorporated thymidine to the nucleus. 3H-Uridine is exclusively incorporated in the chromatin at the beginning of the germination process. The chromatin-dependent RNA synthesis is the first recorded event during reactivation in roots of germinating corn. The resumption of RNA synthesis in the nucleolus and the first appearance of a cytoplasmic labeling after 3H-uridine incorporation occur a few hours later. © 1969."