Development of somatic embryos from morphogenetic cells of the interspecific hybrid Helianthus annuus x Helianthus tuberosus

The morphogenetic competence to differentiate somatic embryos was evaluated in leaf explants of anther-derived plants (EMB-1 clone) of the tetraploid interspecific hybrid Helianthus annuus x Helianthus tuberosus. Various combinations of growth regulators were compared. Embryos rapidly formed at high frequency in each media tested, even without growth regulators. Histological analysis showed repeated divisions of cells of the upper epidermis showing densely stained cytoplasm. After 6 days of culture organized structures were observed on the leaf surface. Further, these clusters of cells increased their volume by division; embryoids developed asynchronously in large numbers over small areas of the leaf. Somatic embryos appeared variously malformed and sometimes they proliferated to produce additional accessory embryos from one morphogenetic unit. Nevertheless, phenotypically normal plants were easily recovered from somatic embryos. The direct embryogenesis observed in each media tested indicates that the somatic cells of EMB-1 plants are already predetermined as embryogenic cells. These cells do not lose their wide competence in the differentiation process and retain the full morphogenetic potential typical of the zygotic cell. This assumption is strengthened by the ability of leaf explants to differentiate embryos without signals of hormonal nature.