Studies on the Organogenesis in Carrot Tissue Cultures I. Effects of Growth Regulators on Somatic Embryogenesis and Root Formation

The effects of various growth regulators on in vitro organogenesis of hypocotyl segments of Daucus carota L. cv. US-Harumakigosun are described. IAA, NOA, IBA and NAA induced roots at lower concentrations and somatic embryos at higher concentrations. The short term application (twO weeks)of 2,4-D greatly stimulated the formation of somatic embryos, and continuous application induced yellowish nodular calluses which possess embryonal potential. The effects of some phenoxyacetic acid derivatives on the organogenesis were also tested. POA stimulated neither root nor somatic embryo formation. OCP A only slightly stimulated root formation, while 2,4,5-T, MCPA, and PCPA stimulated somatic embryo formation. Cytokinins suchas BA and Z, and 4-PU, an aromatic urea having cytokinin activity, did not induce any organogenesis. However, the application of BA with IAA strongly inhibited the root-inducing action of IAA and induced only soft friable calluses. The short­term application of BA plus 2,4-D also induced only soft friable calluses suppressing somatic embryo formation. The effects of various other growth regulators such as AMO-1618, TIBA, 2,6-D, ABA, GAs and coumarin were examined in suspension cultures of carrot cells. GAs, ABA, and AMO-1618 inhibited somatic embryo formation, but TIBA and 2,6-D slightly stimulated it at lower concentrations.