Roles of Auxin and Cytokinin in Organogenesis in Torenia Stem Segments Cultured in vitro.

The physiological roles of auxin and cytokinin on adventitious organ differentiation were examined using Torenia stem segments cultured in vitro. The number of meristematic zones initiated in the epidermis and of adventitious buds developed from these meristematic zones progressively increased with rising concentrations of cytokinin. Zeatin-stimulated formation of meristematic zone was suppressed by a simultaneous application of IAA or anti-cytokinin. At low concentrations, anti-auxin applied either with or without cytokinin promoted the formation of meristematic zone. Adventitious roots were induced only when expiants were treated with IAA or NAA at a concentration higher than 0.05 μM. The number of roots formed as a result of treatment with IAA was strongly reduced by the addition of cytokinin or antiauxin. Application of anti-cytokinin together with IAA slightly stimulated root formation. The present studies confirm that cytokinin plays a major role in adventitious bud differentiation and that auxin plays a similar role in root formation in Torenia stem segments cultured in vitro.