Key message

The anatomical and histochemical localization at subsequent stages of somatic embryogenesis in Santalum album revealed the direct development of somatic embryos from internode explants.

Abstract

Santalum album L. (Santalaceae) is a vulnerable tree species due to overexploitation for commercial, pharmaceutical and cosmetic industries, which necessitate improving the existing in vitro propagation systems for effective plant production and conservation. To date, there is no report on the histochemical basis of somatic embryogenesis in this species. Hence, this study aimed to induce direct somatic embryos (SEs) from the internode explant and to analyze the developmental anatomy and histochemical features during direct somatic embryogenesis. Somatic embryos were induced on Murashige and Skoog (MS) medium with 2.5 mg L⁻¹ 6-benzylaminopurine (BAP), 0.5 mg L⁻¹ 1-naphthaleneacetic acid (NAA), 50 ml L⁻¹ deproteinized coconut water (CW) and 25 mg L⁻¹ each of myo-inositol, adenine sulphate and l-arginine. Pre-treatment of explants with 50 mg L⁻¹ citric acid and ascorbic acid for 0.5 h at 4 °C, and the addition of CW in the medium, favored high-frequency somatic embryogenesis from internode. The light microscopic analysis revealed the development of embryonic cells, vasculature and primary globular stage to matured dicotyledonous embryos. The contents of lignin, cellulose and starch were low in the embryogenic regions, whereas deposition of phenolic compounds, polyphenols, lipids and polysaccharides were found increased in somatic embryos. Embryos germinated well (98%) and the shoots were proliferated on MS medium supplemented with 1.0 mg L⁻¹ BAP, 0.5 mg L⁻¹ NAA and 50 ml L⁻¹ CW. The well-developed shoots were rooted within four weeks on MS medium containing 1.5 mg L⁻¹ indole-3-butyric acid (IBA) and successfully acclimatized in a greenhouse. The highest (97%) survival success was achieved in the field conditions. Thus, the present work has established a novel protocol for induction of somatic embryogenesis from internode explants complemented with studies of the histo-anatomical developments of the SEs. This could help to understand the embryogenic pathway and represent an alternative way of production plantlets for the conservation of S. album.

中文翻译：

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Santalum album L 体细胞胚胎发生过程中不同解剖学特征和初级和次级代谢物特征的组织化学基础。

关键信息

Santalum专辑中体细胞胚胎发生随后阶段的解剖和组织化学定位揭示了节间外植体的体细胞胚胎的直接发育。

摘要

由于商业、制药和化妆品行业的过度开发，Santalum album L.（檀香科）是一种脆弱的树种，需要改进现有的体外繁殖系统以实现有效的植物生产和保护。迄今为止，还没有关于该物种体细胞胚胎发生的组织化学基础的报道。因此，本研究旨在从节间外植体诱导直接体细胞胚胎 (SE)，并分析直接体细胞胚胎发生过程中的发育解剖和组织化学特征。在含有 2.5 mg L ^-1 6-苄氨基嘌呤 (BAP)、0.5 mg L ^-1 1-萘乙酸 (NAA)、50 ml L ^-1脱蛋白椰子水 (CW) 和25 毫克升^-1肌醇、硫酸腺嘌呤和l-精氨酸。在 4°C 下用 50 mg L ^-1柠檬酸和抗坏血酸预处理外植体0.5 小时，并在培养基中加入 CW，有利于节间高频体细胞胚胎发生。光学显微镜分析揭示了胚胎细胞、脉管系统和初级球状阶段到成熟双子叶胚胎的发育。胚发生区木质素、纤维素和淀粉含量较低，而体细胞胚中酚类化合物、多酚、脂质和多糖的沉积增加。胚胎发芽良好 (98%) 并且芽在补充有 1.0 mg L ^-1 BAP、0.5 mg L ^{-1 的}MS 培养基上增殖NAA和50ml L ^-1 CW。发育良好的枝条在 4 周内在含有 1.5 mg L ^-1吲哚-3-丁酸 (IBA) 的MS 培养基上生根，并在温室中成功驯化。在野外条件下取得了最高 (97%) 的存活成功率。因此，目前的工作已经建立了一种新的协议，用于从节间外植体诱导体细胞胚胎发生，并辅以对 SE 的组织解剖学发展的研究。这可能有助于了解胚胎发生途径，并代表了一种用于保护 S.album 的生产小苗的替代方式。