Histological changes associated with acquisition of competence for shoot regeneration in leaf discs ofSaintpaufla ionantha xconfusa hybrid (African violet) cultured in vitro.

In leaf discs ofSaintpaulia ionantha xconfusa hybrid (cv. Virginia) cultured on shoot-inducing medium, periclinal divisions were initiated in epidermal cells 3-5 days after explant isolation. This timing coincided with the time for competence acquisition determined in tissue-transfer experiments. Some of the daughter cells from periclinal divisions formed the target cells which divided both anticlinally and periclinally to form cell division centers (meristemoids), precursors of adventitious shoots. The target cells were not morphologically distinct from other epidermal cells at the light microscope level. It is suggested that the periclinal divisions in epidermal cells represent the dedifferentiation phase during which target (competent) cells are formed. Once the cells have acquired the ability to divide periclinally, both dedifferentiation and shoot induction occur in the presence of exogenous plant hormones.