Histodifferentiation of oil palm somatic embryo development at low auxin concentration

Morpho-histology of co-occurrence of somatic embryos, shoots, and inflorescences within a callus of Limonium 'Misty Blue'

This is the first attempt to report the co-occurrence of somatic embryos, shoots, and inflorescences and their sequential development from stem cell niches of an individual callus mass through morpho-histological study of any angiosperm. In the presence of a proper auxin/cytokinin combination, precambial stem cells from the middle layer of a compact callus, which was derived from the thin cell layer of the inflorescence rachis of Limonium, expressed the highest level of totipotency and pluripotency and simultaneously developed somatic embryos, shoots, and inflorescences. This study also proposed the concept of programmed cell death during bipolar somatic embryo and unipolar shoot bud pattern formation. The unique feature of this research was the stepwise histological description of in vitro racemose inflorescence development. Remarkably, during the initiation of inflorescence development, either a unipolar structure with open vascular elements or an independent bipolar structure with closed vascular elements were observed. The protocol predicted the production of 6.6 ± 0.24 and 7.4 ± 0.24 somatic embryos and shoots, respectively, from 400 mg of callus, which again multiplied, rooted, and acclimatised. The plants' ploidy level and genetic fidelity were assessed randomly before acclimatisation by flow cytometry and inter simple sequence repeats (ISSR) marker analysis. Finally, the survivability and flower quality of the regenerated plants were evaluated in the field.

High-Efficiency Somatic Embryogenesis from Seedlings of Koelreuteria paniculata Laxm

Research Highlights: In the current study, we established a method for plant regeneration via somatic embryogenesis (SE) in Koelreuteria paniculata Laxm. for the first time. Background and Objectives: K. paniculata is an important ornamental and medicinal plant in China. However, the plant has difficulty with asexual reproduction, which imposes a limitation on large-scale propagation. Materials and Methods: Embryogenic calluses were induced from stems of aseptic seedlings on induction media. The effects of different media types and concentrations of N6-benzyladenine (BA), α-naphthaleneacetic acid (NAA), and 2,4-dichlorophenoxyacetic acid (2,4-D) on callus induction were examined. Embryogenic calluses were then transferred to Driver-Kuniyuki Walnut (DKW) media containing NAA (0.1–0.2 mg L−1) or 2,4-D (0.5–2.0 mg L−1) to develop somatic embryos. Cotyledon embryos were cultured on DKW media containing NAA (0.1–0.2 mg L−1) until maturation, and were then transferred to 1/2 DKW medium supplemented with 1.0 mg L−1 indole-3-butyric acid (IBA) to produce complete plants. The effects of IBA and NAA on rhizogenesis were then examined by clonal culture. Results: The maximum callus induction frequency (80.25%) was obtained on DKW medium supplemented by 0.5 mg L−1 BA, 0.25 mg L−1 NAA, and 1.5 mg L−1 2,4-D. NAA had a more pronounced effect on somatic embryo growth than did 2,4-D, with a maximum SE frequency (54.75%) observed with 0.1 mg L−1 NAA added to DKW medium. For clonal culture, the highest rooting rate (52%) was observed on 1/4 DKW medium containing 1.5 mg L−1 IBA. Histology studies confirmed the presence of embryogenic calluses and somatic embryos in different stages. Conclusions: This protocol provides a novel method for large-scale propagation of K. paniculata, and creates opportunities for genetic engineering in this species.