Anatomical differences between embryogenic and non-embryogenic calli of Pimpinella brachycarpa were investigated by light microscopy and electron microscopy. Initial callus tissue emerged from explants after 14 d of culturing. The embryogenic calli (EC) were firm, rather opaque, and light yellow in color. The cells usually formed small, compact clusters. Nonembryogenic calli (NEC), however, were friable, semitransparent, and yellow or gray. These formed relatively larger and loosely held clusters. Scanning electron microscopy showed that EC were composed of individual compact and spherical cells that were rather regular in size and approximately 20 ~tm long. All were tightly held together and appeared to organize globular embryos. In contrast, the NEC comprised elongated and loosely held cells that were approximately 50 ~m long. Tubular and u-shaped NEC cells protruded irregularly, and were of varying heights along the cell aggregates. Transmission electron microscopy of the EC revealed typical eukaryotic cytoplasmic components, including nuclei, mitochondria, and vacuoles in the cytoplasm enclosed by an electron-transparent cell wall. Based on the numerous ribosomes within the cytoplasm, these cells appeared to be well-organized and metabolically active. The NEC cells were much larger and more highly vacuolated than those of the EC. In ultrathin sections, the former seemed to be almost devoid of other cellular contents except for plastids and nuclei. Furthermore, EC and NEC showed different regeneration capacities in their somatic embryo formation. Most EC produced hyperhydric somatic embryos, followed by normal somatic embryos; whereas only a few shooted or rooted somatic embryos arose from the NEC.

Pimpinella brachicarpa (Chamnamul in Korean) is an indigenous plant that grows in Korean mountain areas. It has not been cultivated yet but is gathered to use as a vegetable. Its difficulty of propagation by seeds is one of the major reasons not to be cultivated as a horticultural crop despite its demand. As a promising propagation method for the Chamnamul, we have developed a micropropagation system using somatic embryogenesis. In the present study, induction of embryogenic callus of the Chamnamul affected by part of explants (leaf and stem) and concentration (0, 0.1, 0.5, 1.0, 1.5, and 2.0 mg·L-1) of growth regulators (2.4-D, IAA, IBA, and NAA) was investigated to find the best conditions for embryogenic callus induction. A full strength of MS medium was used for a 50-day culture for all the treatments. The embryogenic callus was firm and light yellow in color and was distinct from the non-embryogenic callus that was friable and semitransparent. More embryogenic callus was induced in the treatments that the stem was used as an explant comparing with the treatments that the leaf was used. The 2.4-D treatments resulted in the better induction of embryogenic callus than other growth regulator treatments, and 1.5 mg·L-1 was the most effective among all the 2,4-D concentration treatments. Addition of 0.1 mg·L-1 BA to 2.4-D treatments retarded the induction of embryogenic callus of the Chamnamul, while the promotion of induction and multiplication of embryogenic callus was reported in many plant species by adding BA with low concentration to an auxin-base medium. The better induction was found in the treatments of darkness and dim lighting (10 μmol·m-2·s-1 of PPF) than in treatments of the higher PPF.