Involvement of Calcium in Adventitious Bud Initiation in Torenia Stem Segments

In Torenia stem segments cultured in vitro, active meristematicdivisions are induced in the epidermis by treatment with cytokinin,resulting in the formation of adventitious buds. Applicationof the calcium ionophore A23187[GenBank] was found to induce meristematicdivisions in the absence of cytokinin. The induction by A23187[GenBank]was inhibited by simultaneous addition of auxin, but not byanti-cytokinin. A two hour pre-treatment with A23187[GenBank] was alsoeffective, but only when it was applied to the explants justafter their excision from mother plants. The A23187[GenBank]-inducedmeristematic zones developed into dome-shaped structures, butnot into complete adventitious buds. Complete elimination ofcalcium from the culture medium caused 50% inhibition of A23187[GenBank]-and/or cytokinin-induced initiation of meristematic divisions.When the explants were preincubated with EGTA and then culturedon a Ca-free medium containing EGTA, cytokinin failed to inducebud initiation. Similar inhibition was also obtained by lanthanum,a calcium antagonist, by verapamil, a calcium channel inhibitor,and by trifluoperazine and chlorpromazine, calmodulin inhibitors.These results support the idea that adventitious bud initiationinduced by cytokinin in Torenia stem segments may be mediated,at least partially, by an increase in the level of intracellularCa²⁺. ¹Bioscience Research Center, Mitsui Petrochemical IndustriesLtd., Waki-cho, Kuga-gun, Yamaguchi 740, Japan. (Received May 9, 1985; Accepted October 5, 1985)