Explant type and stress treatment determine the uni- and multicellular origin of somatic embryos in the tree fern Cyathea delgadii Sternb.

Abstract

Cyathea delgadii is the first fern species for which somatic embryogenesis (SE) has recently been described. With this discovery, a new experimental model for exploration of SE was found. In this study, the effect of explant type (stipe and internode), length and diameter of the explant-donor frond, and stress treatment (by sucrose and air desiccation) on somatic embryo origin and SE efficiency was studied. In control culture, somatic embryos originated from single cells of stipe explants, whereas those induced on internodes were of multicellular origin. Although the activation of cell divisions was more abundant and the formation of somatic embryos occurred earlier in a culture of internodes than of stipe explants, the morphogenic capacity of internodes was much smaller. On their surface, the groups of competent cells formed protuberances that give rise to only three somatic embryos per internode. In contrast, almost 92% of stipe explants that were excised from the first frond, measuring 10 mm in length and less than 300 µm in diameter, produced an average of 21 somatic embryos. Stipes treated with sucrose were not able to SE. More than fourfold increase in SE efficiency was obtained on internodes by their treatment with 0.4 M sucrose for 45 min. It was achieved by changing the pathway of somatic embryo differentiation from multicellular to unicellular. These results provide an excellent basis for further research on the mechanism of SE induction associated with a single-and multi-cell proliferation, especially that both types of the embryogenic pathway can occur on the same hormone-free medium.

Signaling Overview of Plant Somatic Embryogenesis

“…Different studies support the theory that the first stages of SE are characterized by the induction of numerous genes related to stress such as those discussed later on this review (Nic-Can et al, 2016; Nowak and Gaj, 2016). Recent evidence in potato (Kaur et al, 2018), Pinus sylvestris (Salo et al, 2016), Picea asperata (Jing et al, 2017), Oldenlandia umbellata (Krishnan and Siril, 2017), and Cyathea delgadii (Grzyb and Mikula, 2019) has revealed that the presence of different types of stress plays an essential role in the induction of SE. The main stress for cells during the induction of SE is the presence of high auxin concentration in the culture medium.…”

Comparative Transcriptomics of Non-Embryogenic and Embryogenic Callus in Semi-Recalcitrant and Non-Recalcitrant Upland Cotton Lines

“…Plant somatic embryogenesis (SE) is a unique developmental process that ultimately leads to the regeneration of a whole plant from single or multiple somatic cells [ 1 ]. This process involves sophisticated cellular reprogramming events that are controlled by gene expression programs and signaling pathways that direct callus cells to dedifferentiate, reprogram, and begin differentiation into polarized structures that eventually become a viable embryo [ 2 , 3 , 4 , 5 ].…”

Symplasmic Isolation Contributes to Somatic Embryo Induction and Development in the Tree Fern Cyathea delgadii Sternb

“…The pathway of somatic embryo initiation and development in C. delgadii explants depends on such artless factors as length and diameter of the explant-donor frond, type of explant, as well as physical and chemical factors of media and culture conditions ( Mikuła et al. 2015a , Grzyb and Mikuła, 2019 ). One of the basic triggers inducing SE is the light conditions for donor plantlet growth ( Mikuła et al.…”