HISTOLOGICAL ANALYSIS OF SOMATIC EMBRYOGENESIS INDUCED IN TROPICAL LADY'S SLIPPER ORCHID (PAPHIOPEDILUM NIVEUM)

Indirect somatic embryogenesis, an asexual process of plant propagation, is an acceptable tool for cell differentiation and developmental studies. This study was conducted to elucidate the developmental pathway of a somatic embryo in the Paphiopedilum niveum orchid. The callus-derived somatic embryo was obtained by using modified Vacin and Went (VW) medium supplemented with 0.1 mg L^-1 naphthalene acetic acid (NAA) and 0.5 mg L^-1 thidiazuron (TDZ) as well as 10 g L^-1 sucrose. Developmental phases were characterized by histological analysis. The callus-derived somatic embryos developed progressively through the early globular, globular and cotyledonary stages. After a month of culture, a proembryonic mass (or early globular-shape stage) originated on the surface of the callus and differentiated rapidly to a globular somatic embryo with a well-demarcated protoderm. These somatic embryos developed protrusions that indicated the cotyledonary stages after two months of culture. The organized structures of plantlets were eventually obtained when protocorm-like bodies (PLBs) involving somatic embryogenesis were transferred to modified Murashige and Skoog (MS) medium supplemented with 50 g L^-1 homogenated banana. Histological analysis also revealed that the pattern of somatic embryo formation of P. niveum showed the same process as the developmental pathway of monocot species.