Is DNA synthesis required for the induction of differentiation in quiescent root cortical parenchyma?

Cortical parenchyma of pea roots normally does not divide nor differentiate as tracheary elements. After excision from the root these cells can be induced to undergo cell division followed by differentiation of tracheary elements in the presence of cytokinin. 5-Fluorodeoxyuridine prevents cell replication and cytodifferentiation. The thymidine analog, 5-bromodeoxyuridine, specifically prevents cytodifferentiation with little or no effect on the rate of cell replication. Thymidine can also prevent cytodifferentiation with little effect on cell replication. Thymidine reverses the effect of 5-bromodeoxyuridine (BrdU) or 5-fluorodeoxyuridine (FdU) when given simultaneous with or subsequent to either BrdU or FdU. BrdU given with FdU allows up to one round of cell replication but no cytodifferentiation. Differentiation is rarely observed unless the entire cell population has undergone the equivalent of two cell generations. These results are combined with those of other investigators to present an hypothesis that implicates DNA replication but not cytokinesis in the regulation of certain types of differentiation.