Histological observation of somatic embryogenesis from cultured embryos of Quercus variabilis Bl

Immature zygotic embryos of Quercus variabilis Bl. were excised and cultured on MS basal medium containing 0.25 mg/L 2,4-dichlorophenoxyacetic acid and 0.5 mg/L 6-benzyl aminopurine. Callus was initiated from these embryos within 6 weeks. Two types of embryogenic calluses were formed: one was the white mucilaginous callus and the other was light yellow to translucent, glossy, mucilaginous. Histological examination showed that the non-embryogenic cells derived from zygotic embryos were large in size, with small nuclei, thin cytoplasm, and the embryogenic cells were small in size, with large nuclei, thick cytoplasm and denser arrangement. Somatic embryos were induced from embryogenic masses (EMS) cultured on a medium not containing plant growth regulators (PGRs). The histological origin of somatic embryos was single epidermal or subepidermal cells. Somatic embryos displayed a standard development pattern, from globular ones to heart-like and torpedo-shaped ones and finally to embryo with two cotyledons, which was similar to the development of zygotic embryo in vivo. Secondary proembryos were formed on the axis and cotyledon of existing embryos and originated from single, densely stained cells of the epidermis at all stages.