Hormonal control of inflorescence development in plantlets of calla lily (Zantedeschia spp.) grown in vitro

Hormonal control of flower induction and inflorescence development in vitro was investigated in photoperiodically day-neutral calla lily (Zantedeschia spp., colored cultivars). The effects of gibberellins (GAs, 5.8-2900 micromolar) and the cytokinin benzyl adenine (BA, 0.4-13.3 micromolar) on inflorescence development were studied in plantlets regenerated in tissue culture. Plantlets were dipped in GA and BA solutions prior to replanting in new media. GA was mandatory for the shift from the vegetative to the reproductive stage. GA3, GA1 and GA4 had the same florigenic effect. Inflorescence development in the apical bud was observed after 30-50 days in GA-treated plantlets grown in vitro and resembled the pattern occurring under natural conditions. The transition from the vegetative to the reproductive phase was characterized by a swollen, dome-shaped apex that transformed into a smooth elongated apex surrounded by the spathe primordium, at the tip of the elongating peduncle primordium. Floret primordia developed in inflorescences at a more advanced stage. The female florets located at the base of the primordial spadix, could be clearly distinguished from male florets located above them. BA did not have an effect on flower induction but, in the presence of GA, BA at concentrations up to 4.4 micromolar enhanced inflorescence differentiation. The results indicate that inflorescence development in Zantedeschia plantlets in tissue culture can serve as a potential model to study the role of GAs and other factors in the flowering process of day-neutral plants that do not require external signals for flower induction.