ABSTRACT
The life cycle of higher plants includes the following two generations: a haploid or gametophytic generation, and a diploid or sporophytic generation. The sporophytic generation begins with the double fertilization process that results in the formation of a zygote embryo and an endosperm nucleus. The embryogenesis pathway, which represents the critical transition during zygote embryo development, can be divided into the following stages: globular-shaped, heart-shaped, torpedoshaped, and cotyledonal stages in dicots; globular scutellar and coleoptilar stages in monocots; and globular, early cotyledonary, and late cotyledonary embryos in conifers. Completion of the stages results in the generation of a new plant. Alternatively, the plant can be derived from a single somatic cell or a group of somatic cells. This regeneration process, which differs from the zygote embryo pathway, is known as somatic embryogenesis or nonzygotic embryogenesis. Here after we will refer to the process as somatic embryogenesis.
