Abstract
Dynamic changes in callose content, which is deposited as a plant defense response to physiological changes, were analyzed during somatic embryogenesis in Eleutherococcus senticosus zygotic embryos plasmolyzed in 1.0 M mannitol. During plasmolysis, callose deposition was clearly observed inside the plasma membrane of zygotic embryo epidermal cells using confocal laser scanning microscopy. The callose content of zygotic embryos gradually increased between 0 and 12 h plasmolysis and remained stable after 24 h plasmolysis. During eight weeks induction of somatic embryogenesis, the callose content of explants plasmolyzed for 12 h was slightly higher than explants plasmolyzed for 6 or 24 h, with the largest differences observed after 6 weeks culture, which coincided with the maximum callose content and highest number of globular somatic embryos. The highest frequency of somatic embryo formation was observed in explants plasmolyzed for 12 h. The somatic embryo induction rate and number of somatic embryos per explant were markedly different in zygotic embryos pretreated with plasmolysis alone (78.0%, 43 embryos per explant) and those pretreated with plasmolysis and the callose synthase inhibitor 2-deoxy-d-glucose (11.5%, 8 embryos per explant). This study indicates that callose production is required for somatic embryogenesis in plasmolyzed explants.
Highlights
Somatic embryogenesis (SE) has been studied as a model system to understand the physiological, biochemical and genetic events during plant embryo development at a molecular level [1]
Callose deposition was clearly observed inside the plasma membrane of epidermal cells in zygotic embryos plasmolyzed in 1.0 M mannitol for 12 h using confocal laser scanning microscopy (CLSM) (Figure 1c,d)
(a,b) Callose deposition was not observed in the hypocotyl epidermis of untreated zygotic embryos. (c,d) Callose deposition was observed in the cytoplasm of plasmolyzed cells in the hypocotyl epidermis of zygotic embryos pretreated with 1.0 M mannitol for 12 h
Summary
Somatic embryogenesis (SE) has been studied as a model system to understand the physiological, biochemical and genetic events during plant embryo development at a molecular level [1]. Stress treatment of explants at the initial stage of culture or during SE has increasingly been recognized as playing an important role in the induction of SE [2,3]. Callose plays a very important role in plant developmental processes and in the response to various biotic and abiotic stresses [11]. Callose deposition has been observed during SE in some species, which is generally initiated by stress pretreatment. PGRs. After six days culture, the cytoplasmic content of some epidermal and subepidermal cells was denser and callose deposition was observed, which did not disappear until the formation of a 50-μm diameter proembryo group. Callose deposition was observed in E. senticosus zygotic embryos in response to mannitol and sucrose plasmolysis. We examined the effects of callose deposition in plasmolyzed explants on SE, and the dynamic changes in callose content during SE
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