POSSIBLE INVOLVEMENT OF DNA-REPAIR EVENTS IN THE TRANSDIFFERENTIATION OF MESOPHYLL CELLS OF ZINNIA ELEGANS INTO TRACHEARY ELEMENTS

摘要

In cultures of isolated mesophyll cells of Zinnia elegans, transdifferentiation into tracheary elements is induced by a combination of auxin and cytokinin and is blocked by inhibitors of DNA synthesis and poly (ADP-ribose) synthesis. During transdifferentiation, a very low level of synthesis of nuclear DNA was found in some cultured cells by microautoradiography after pulse-labeling with [H-3]thymidine. Density profiles of nuclear DNA that had been double-labeled in vivo with bromodeoxyuridine (BrdU) and [H-3]thymidine indicated that this DNA synthesis was repair-type synthesis. The sedimentation velocity of nucleoids increased during the culture of isolated mesophyll cells and the increase was dependent on phytohormones. This phenomenon may reflect the rejoining of DNA strand breaks after repair-type DNA synthesis during transdifferentiation. Treatment of cells with inhibitors of DNA synthesis or of poly(ADP-ribose) synthesis prevented the increase in the sedimentation velocity of nucleoids. The data suggest the involvement of DNA-repair events in the transdifferentiation of mesophyll cells into tracheary elements.