The Effect of 1,4-Dihydropyridines on the Initiation and Development of Gametophore Buds in the Moss Funaria

The plant hormone cytokinin stimulates target caulonemata of Funaria to form buds that develop into the leafy gametophyte. Previous reports have shown that increases in intracellular Ca(2+) occur during hormone-activated budding concomitant with an alteration in the polarity of the organelles in the bud site. In order to ascertain the involvement of voltage-dependent Ca(2+) channels in this phenomenon, we have employed dihydropyridines (DHP), compounds noted for their ability to alter Ca(2+) flux through potential-sensitive channels. Addition of the DHP agonists (+)202-791 and CGP 28392 (100 micromolar) induces bud initials on every target cell including the tip cell. Application of the DHP antagonist (-)202-791, in the presence of cytokinin (1 micromolar benzyladenine), inhibits budding 96%. Similarly, nifedipine blocks cytokinin-induced budding 87% and its effect on budding can be inactivated with a pulse of ultraviolet light. These results are consistent with the idea that cytokinin induces the budding response by increasing Ca(2+) entry through voltage-operated channels. We suggest that cytokinin activation of Ca(2+) channels is the first action of the hormone and that subsequent cytokinin-induced mechanisms are operating to maintain budding, since DHP-induced initials rarely develop into complete buds.