Green Globular Body (GGB) Induction and Differentiation in the Medicinal fern Drynaria Roosii

Abstract

Background: The green globular body (GGB) of ferns is a special propagule induced in plant in vitro culture systems. Owing to its high proliferation efficiency, GGB is widely used in the in vitro propagation of important ornamental and medicinal ferns. In addition, propagation using GGB shows great development prospects in the conservation of rare or endangered ferns and the breeding of new fern varieties. However, due to the lack of systematic studies on GGB ontogenesis, the morphogenetic aspects of GGB during induction and differentiation remain unclear.Results: We characterized the response of five types of explants of Drynaria roosii to GGB inductive medium and further investigate morphological and anatomical changes of explants that developed GGBs. We found that the rhizome explants directly produced GGBs through cell proliferation of the shoot apical meristem and lateral meristem. The leaf and petiole explants produced GGBs indirectly through the proliferation of meristematic cells of somatic embryos derived from the epidermal cells of the explants. The root and gametophyte explants failed to produce GGB under our induction conditions. We further investigated the differentiation process of GGB. During GGB differentiation, shoot primordia and leaf primordia differentiate from meristematic cells on the epidermis, and the root primordia develop from an inner meristematic tissue with developing vascular tissue connecting all these primordia, which indicates the involvement of multiple organogenesis processes.Conclusions: Our results suggested that preexisting or reestablished meristematic cells were the direct source of GGB in D. roosii. Somatic embryogenesis and organogenesis were involved in GGB induction and differentiation, respectively. The comparison with other common propagules revealed that GGB in D. roosii was largely different from somatic embryos, callus, and protocorm or protocorm-like bodies.