The effect of gibberellin and cytokinin on floral development in zantedeschia spp. in vivo and in vitro

Zantedeschia spp. (Araceae) is a tuberous day-neutral plant in which flowering is not induced by environmental signals. Flower yield, however, is increased by treatments with gibberellin A3 or gibberellin A₄₊₇ and benzyl adenine (BA). We examined the effect of GA3 and BA on inflorescence differentiation in three experimental systems: sprouting tubers, intact growing plants and plantlets in tissue culture. A similar pattern of response was found in all the experimental systems. One application of GA3 resulted in inflorescence differentiation in the apical bud of the main shoot on the tuber as well as in plantlets in vitro. Continuous application of BA weakened apical dominance imposed by the main shoot and thus enabled the sprouting of inhibited axillary buds. Application of BA accompanied by one application of GA3 resulted in inflorescence differentiation in the apical and axillary buds in the main and secondary shoots of the tuber as well as in plantlet in vitro. Thus, BA affected flowering indirectly by promoting axillary bud growth that responded to the GA3 treatment. These results suggest that in day-neutral Zantedeschia the meristem is responsive to GA3 regardless of tuber size, plant age, or meristem position. A change in GA3 level may play a central role in the transition from the vegetative to the reproductive stage, and both gibberellins and cytokinins are involved in floral initiation and development. Plantlets in vitro can serve, therefore, as a model system for studying inflorescence development in day-neutral plants.