Morphological and histological characteristics of somatic embryo development of carrot (Daucus carota L.)

Embryogenic callus formation was induced from the cultures of hypocotyl explants of Daucus carota L. on Murashige and Skoog (MS) medium containing 1.0 mg/L 2,4-dichlorophenoxyacetic acid. Liquid cultures of the embryogenic cells or clumps were maintained on a shaker at 120 strokes/min, and then the embryogenic cells or clumps were sub-cultured in hormone-free MS medium for two weeks to develop somatic embryos. Somatic embryos obtained from the liquid cultures were classified as somatic embryos (two cotyledons) and abnormal multi-cotyledons (three or four cotyledons). The differentiation of procambial tissue in the somatic embryos initiated with a circular shape in the hypocotyl region and then connected to the cotyledon nodes; the tissue differentiated into the cotyledon region to form two cotyledons with two procambial strands, three cotyledons with three procambial strands, and four cotyledons with four procambial strands. These results suggest that the differentiation of procambium in somatic embryos is closely related to the number of cotyledons formed.