| Available protocols for Capsicum annuum genetic transformation are not completely reproducible since this species is recalcitrant to both in vitro regeneration and transformation. Therefore, our working hypothesis was based on the possibility of increasing the small overlap of cell populations competent to regenerate and competent to be transformed in explants from C. annuum and C. baccatum.; Regeneration experiments done with cotyledons, leaf disks, rooted hypocotyls, still bent rooted hypocotyls at germination (‘hooks’), zygotic embryos, root-side half-seeds and ‘organogenetic callus’ led to the definition of an appropriate culture medium, concentration of antibiotics for selection of transformants and the inclusion of antioxidants.; After regeneration media definition, 24 transformation experiments including six explants from both ‘NM6-4’ (C. annuum) and ‘Campanita’ (C. baccatum) cultivars cocultured with A. rhizogenes K599 and A. tumefaciens EHA105 were performed. Stable transformation percentage (based on GUS expression) of adventitious buds was found to be the highest (up to 23.3%) on experiments that included A. tumefaciens EHA105 and ‘Campanita’ inverted ‘hooks’ and hypocotyls. Experiments using ‘NM6-4’ ‘hooks’ and A. tumefaciens EHA105 showed 8.3% of GUS positive regenerating explants. Water-bath sonication and vacuum infiltration during cocultivation induced little or no transformation improvement.; Organogenetic calluses were characterized by origin and morphological features. Additionally, their necrotic responses after coculture with Agrobacterium were related to peroxidase activity and phenolics content. Twenty percent of half seeds (original explants) succeeded to develop into organogenetic calluses. These calluses showed three callus ‘subtypes’: a whitish friable callus, a hard green callus with no buds, and a bud mass mounted on green callus. Since the last one was capable of regenerating complete plants it was used in transformation experiments. Nevertheless, dramatic necrosis was apparent on all explants after coculture. This event was related with a little increase of peroxidase level for five days and a decrease in the content of soluble phenolics. Comparison of organogenetic calluses against other Capsicum calluses or plants indicate a probable inverse correlation between peroxidase activity and phenolic content. |
