Explant Type, Culture System, 6-Benzyladenine, Meta-Topolin and Encapsulation Affect Indirect Somatic Embryogenesis and Regeneration in Carica papaya L.

Abstract

A protocol to propagate papaya hybrid plants through indirect somatic embryogenesis was developed considering the effect of explant type, culture system, particular cytokinins and encapsulation, in different stages of the process. Optimal 2,4-dichlorophenoxyacetic acid (2,4-D) concentrations for non-embryogenic callus formation ranged between 9.0 and 27.1 μM in half-cut seeds, while higher concentrations were harmful. Non-embryogenic callus was also obtained with 22–158 μM 2,4-D from hypocotyl segments. Callus with embryogenic structures was only obtained in half-cut seeds cultured in the darkness on half-strength Murashige and Skoog culture medium supplemented with 2,4-D, while hypocotyl segments and isolated zygotic embryos failed to produce this type of callus regardless of the 2,4-D and sucrose (30 and 70 g l-1) concentrations tested in this study. Both, embryogenic callus development and quantity of somatic embryos formed per embryogenic callus, which ranged between 11 and 31 units after 14 months, required 2,4-D, but without any effect of the concentration. Histological studies confirmed the multicellular origin of the somatic embryos. In further steps, liquid medium induced over four times more somatic embryos than agar-gelled medium and showed significantly higher production of globular somatic embryos (85 vs. 57%). Both, 6-benzyladenine (BA) and meta-topolin (Mtop) stimulated sprouting (40–45%) of the somatic embryos (development of shoots only) in concentrations of up to 2.7 and 10 μM, respectively. Sprouting probability showed a 2nd order polynomial trend despite the range of concentration used for each cytokinin. This is the first report about the positive effect of Mtop on the apical shoot development of Carica papaya somatic embryos known to the authors. Radicle growth was observed in 5% or less of the cultivated embryos, regardless of the BA concentration. Finally, all encapsulation conditions tested (2.5, 3.5, and 4.5% sodium alginate, combined with 50 and 100 mM CaCl2) reduced sprouting of somatic embryos when compared to the non-encapsulated ones, whereas capsule hardness showed low correlation with embryo sprouting. Embryos were further cultivated until they became plantlets approximately 5 cm long. They were acclimatized and afterward planted in the field, where they flowered and produced fruit.

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

“…In direct somatic embryogenesis, cells already have embryogenic competence (specific pre‐embryogenic cells) and require minimal genetic reprogramming (Horstman et al ) for the formation of the embryo, without the stage of de‐differentiation. On the other hand, cells in indirect somatic embryogenesis require more genetic reprogramming to acquire embryogenic competence (induction of certain embryogenic cells), which is preceded by the cell proliferation – calluses (Sharp et al , Williams and Maheswaran , Yeung , Silva et al , Solórzano‐Cascante et al ). According to Horstman et al (), in direct somatic embryogenesis, totipotency‐related genes are more accessible to the transcriptional machinery.…”

Elicitation of the in vitro Cultures of Selected Varieties of Vigna radiata L. With Zinc Oxide and Copper Oxide Nanoparticles for Enhanced Phytochemicals Production

“…In the present study, shoot explant grown in vitro gave better response in shoot culture establishment. Earlier, researchers have reported a predominant effect of explant type on in vitro culture establishment (Hazra et al, 2000 ; Solorzano-Cascante et al, 2018 ).…”

Evolving role of synthetic cytokinin 6-benzyl adenine for drought stress tolerance in soybean (Glycine max L. Merr.)

“…Generally, 6-BAP regulates various aspects of cell division, apical dominance, tissue senescence and translocation of photosynthates from the source to the sinks. 6-BAP in cooperation with other cytokinins or auxins can further control fundamental growth and developmental processes, including direct/indirect somatic embryogenesis, lateral shoot formation and callus initiation under controlled in vitro cell culture conditions (Solorzano-Cascante et al, 2018;Srilestari et al, 2020). However, the 6-BAP levels used in plant tissue culture are generally applied at concentration ranging from 0.01 to 10.0 mgL −1 to stimulate axillary and adventitious shoot proliferation, regulate cell differentiation, activate RNA synthesis, and stimulate protein/enzyme activity (Naito et al, 2006).…”