Histology of somatic embryogenesis of the cycad Ceratozamia mexicana var. Robusta (Miq.) Dyer

Abstract

Embryogenic cultures were initially friable and yellow, and were composed of spherical, vacuolate cells with prominently stained nuclei. Binucleate cells occurred in embryogenic cultures but could not be directly associated with induction of somatic embryogenesis. None of the early stage somatic embryos that formed from the primary cultures developed to maturity. Proliferating embryogenic cultures consisted of hyperhydric somatic embryos that increased in number by cleavage or somatic polyembryogenesis from the embryonic mass. Binucleate cells were also temporally present in the embryonic mass during cleavage or somatic polyembryogenesis; however, it was impossible to relate the appearance of these cells with secondary somatic embryogenesis. Approximately 12–15 months after the first appearance of precotyledonary somatic embryos, the somatic embryos became hard and opaquely white in appearance. The embryonic mass of somatic embryos at this time consisted of very small, actively dividing cells. Cap cells were not observed at the distal end of precotyledonary somatic embryos. Cells of the suspensor were rich in starch, elongated and highly vacuolate. Somatic embryos were dicotyledonary and densely stained idioblasts were observed in the cotyledons. Root initials developed distal to the root cap. The bipolar morphology of these somatic embryos was confirmed.