Involvement of Calcium in Adventitious Bud Initiation in Torenia Stem Segments

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In Torenia stem segments cultured in vitro, active meristematic divisions are induced in the epidermis by treatment with cytokinin, resulting in the formation of adventitious buds. Application of the calcium ionophore A23187 was found to induce meristematic divisions in the absence of cytokinin. The induction by A23187 was inhibited by simultaneous addition of auxin, but not by anti-cytokinin. A two hour pretreatment with A23187 was also effective, but only when it was applied to the explants just after their excision from mother plants. The A23187-induced meristematic zones developed into dome-shaped structures, but not into complete adventitious buds. Complete elimination of calcium from the culture medium caused 50% inhibition of A23187- and/or cytokinin-induced initiation of meristematic divisions. When the explants were preincubated with EGTA and then cultured on a Ca-free medium containing EGTA, cytokinin failed to induce bud 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 initiation induced by cytokinin in Torenia stem segments may be mediated, at least partially, by an increase in the level of intracellular Ca^<2+>.
日本植物生理学会の論文