Abstract
Key message Somatic embryogenesis has never been reported in ferns. The study showed that it is much easier to evoke the acquisition and expression of embryogenic competence in ferns than in spermatophytes. We discovered that the tree fern Cyathea delgadii offers an effective model for the reproducible and rapid formation of somatic embryos on hormone-free medium. Our study provides cyto-morphological evidence for the single cell origin and development of somatic embryos. Somatic embryogenesis (SE) in both primary and secondary explants was induced on half-strength micro- and macro-nutrients Murashige and Skoog medium without the application of exogenous plant growth regulators, in darkness. The early stage of SE was characterized by sequential perpendicular cell divisions of an individual epidermal cell of etiolated stipe explant. These resulted in the formation of a linear pro-embryo. Later their development resembled that of the zygotic embryo. We defined three morphogenetic stages of fern somatic embryo development: linear, early and late embryonic leaf stage. The transition from somatic embryo to juvenile sporophyte was quick and proceeded without interruption caused by dormancy. Following 9 weeks of culture the efficiency of somatic embryogenesis reached 12–13 embryos per responding explant. Spontaneous formation of somatic embryos and callus production, which improved the effectiveness of the process sevenfold in 10-month-long culture, occurred without subculturing. The tendency for C. delgadii to propagate by SE in vitro makes this species an excellent model for studies relating to asexual embryogenesis and the endogenous hormonal regulation of that process and opens new avenues of experimentation.
Highlights
Somatic embryogenesis is the developmental pathway by which plant somatic cells develop into somatic embryos
We discovered that the tree fern Cyathea delgadii offers an effective model for the reproducible and rapid formation of somatic embryos on hormone-free medium
Somatic embryogenesis (SE) in both primary and secondary explants was induced on half-strength microand macro-nutrients Murashige and Skoog medium without the application of exogenous plant growth regulators, in darkness
Summary
Somatic embryogenesis is the developmental pathway by which plant somatic cells develop into somatic embryos. SE is currently used to propagate hundreds of species of seed plant in vitro, and forms the basis of fundamental studies that help us understand how a single somatic cell develops to form an entire plant (Vogel 2005). The process serves as a model system for the study of molecular, biochemical and physiological events that occur during both the induction and the development of the embryo. SE was discovered more than half a century ago (Steward et al 1958), our entire knowledge of this process is based on seed plants.
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