Histology, histochemistry and ultrastructure of pre‐embryogenic cells determined for direct somatic embryogenesis in the palm tree Syagrus oleracea

Abstract

Somatic embryogenesis in palm trees is, in general, a slow and highly complex process, with a predominance of the indirect route and, consequently, a lack of knowledge about the direct route. We present new knowledge related to the morphological, histochemical and ultrastructural aspects of the transition from somatic to embryogenic cells and direct formation of somatic embryos from mature zygotic embryos of Syagrus oleracea, a palm tree. The results support the general concept that 2,4‐dichlorophenoxyacetic acid plays a critical role for the formation of somatic embryos of direct and multicellular origin. Seven days in medium with auxin were enough for the identification of embryogenic cells. These cells had a set of characteristics corresponding to totipotent stem cells. At 14 days on induction medium, nodular formations were observed in the distal region of inoculated embryos, which evolved into globular somatic embryos. At 120 days on induction medium, the quality of the somatic embryos was compromised. The dynamics of the mobilization of reserve compounds was also demonstrated, with emphasis on starch and protein as energy sources required for the embryogenic process. This study shows for the first time the anatomical and ultrastructural events involved in direct somatic embryogenesis in a palm tree and incites the scientific community to return to the discussion of classical concepts related to direct somatic embryogenesis, especially regarding the characteristics and location of determined pre‐embryogenic cells.

Somatic embryogenesis and plant regeneration in Piper aduncum L

“…4c). These characteristics coincide with some of those mentioned in embryogenic calli of other plant species (Corredoira et al 2017;Silva-Cardoso et al 2019).…”

“…The fixation, dehydration, and infiltration processes of the samples were performed according to Silva-Cardoso et al (2019). Blocks were cut longitudinally in 4-μm thickness sect i o n s i n a m a n u a l r o t a r y m i c r o t o m e ( L e i c a ® , RM212RT, Buffalo Grove, IL) and the obtained sections were stained with toluidine blue at acidic pH (O'Brien et al 1964).…”

Direct and Indirect Somatic Embryogenesis Induction in Camellia oleifera Abel

“…(Corredoira et al, 2019;Martínez et al, 2019). Although somatic embryos can be induced from the mature zygote embryos of adult plants (Silva-Cardoso et al, 2020), it seems to be more difficult for developmentally older tissues and organs to induce somatic embryos, especially for most woody plants. Compared with immature explants or embryonic tissues, more reprogramming is required in mature tissues to transform them into somatic embryos (Merkle et al, 1995).…”

Embryonal Masses Induced at High Temperatures in Aleppo Pine: Cytokinin Profile and Cytological Characterization

“…In P. halepensis lipid bodies were also found in all treatments, although more abundantly in the control. Numerous protein bodies of different sizes or lipid bodies were also observed in ECs of other species [54,56]. In the case of P. halepensis, the presence of the above mentioned storage compounds could not be directly correlated with the progress of SE and their function could probably be related with house-keeping functions of the cells more than with a control of the embryogenic process.…”

“…Other authors pointed out that starch, as a primary source of energy for cell proliferation, is abundantly found at competent embryogenic cells that will later differentiate into PEMs. High metabolic activity of these cells will deplete this reserve in such a way that it will no longer be present when embryos start to organize [53,54]. In Picea glauca a precise pattern of storage compound accumulation during SE was identified with the first accumulation of starch further followed by the formation of lipid bodies and protein vacuoles [55].…”