Direct organogenesis from hypocotyl-derived explants of annatto (Bixa orellana)

Paiva Neto, V. B. de; Mota, T. R. da; Otoni, W. C.

doi:10.1023/a:1025063906822

The relative importance of explant, cytokinin type, carbon source and gelling agent for annatto organogenesis was studied. The best organogenic response, including adventitious shoot number and elongation, was obtained when hypocotyl segments and rooted hypocotyls were cultured onto MS medium supplemented with 4.56 micromolar zeatin, 87.6 mM sucrose, and 2.8 g l-1 Phytagel. Adventitious shoots derived from hypocotyl segments were less frequent and more difficult to elongate than those derived from rooted hypocotyls. Thidiazuron (TDZ) promoted a higher organogenic response in rooted hypocotyls, resembling a rosette-like structure, but impaired shoot elongation. Histological investigation showed that zeatin-induced meristemoids originated mainly from wounding tissues, and that TDZ induced a high level of mitotic division resulting in several proliferation zones nearby the epidermis and outer cortical tissues. Rhizogenesis efficiency (rooting frequency and root number) was greater at the highest indole-3-butyric acid (IBA) concentration (5.0 micromolar) employed, although calli occurred at the basal end of shoots. Eighty percent of rooted plantlets survived after acclimatization. This optimized regeneration protocol may enable further development of an efficient genetic transformation protocol for this species.