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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.

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An efficient protocol is reported for in vitro plant regeneration through somatic embryogenesis in Piper aduncum, a Brazilian Amazon species with high economic potential. The species is important due to a variety of components found in its essential oil, with emphasis on dillapiole. Leaf explants from five accessions identified for high oil yield and levels of dillapiole were evaluated for their embryogenic potential. To induce embryogenic calli, the explants were cultivated in MS medium supplemented with 5 mg L −1 of 1-naphthaleneacetic acid (NAA) and 2.5 mg L −1 of N6-benzylaminopurine (BAP) for 80 d. For somatic embryogenesis, the embryogenic calli were transferred to MS medium with 10 mg L −1 of NAA and 2.5 mg L 1 of BAP and incubated for 45 d. The obtained somatic embryos were germinated in MS medium without regulators by 45 d and the obtained plantlets were subjected to acclimatization. Somatic embryos and calli from this process were subjected to anatomical and histochemical analyses. Biochemical analyses (total soluble sugars, starch, total amino acids, and proteins) were also performed to identify markers for embryogenic competence acquisition. In addition, the germination of somatic embryos was evaluated in a semi-solid and liquid system (R.I.T.A.® temporary immersion bioreactors). The obtained plants were evaluated for genetic fidelity using ISSR markers. The present study indicate that the accessions did not differ in embryogenic potential, with a mean percentage of calli with somatic embryos of 82.4%. Anatomical analyses confirmed the occurrence of the embryogenic route and the histochemical analyses identified starch grains in somatic embryos at different developmental stages. The biochemical analyses showed high total soluble sugars and total amino acids in embryogenic calli, marks of the acquisition of the embryogenic competence of P. aducum. The R.I.T.A.® temporary immersion bioreactors were highly efficient in the regeneration of somatic plants, with 100% germination. The plants regenerated in the semi-solid and liquid systems showed high genetic homogeneity. The survival rate of the acclimatized plants was 100%.

This paper, in an unprecedented way, describes the ontogenesis of calli and somatic embryos of macaw palm (Acrocomia aculeata) from young leaf tissues of adult plants, aiming to elucidate the events underlying the process and consequent optimization of the technique. Leaves were inoculated in a callus induction medium, composed of Y3 salts, 2.5 g L −1 activated charcoal and 450 μM Picloram. For multiplication of the calli, they were separated from the explants and inoculated in a medium with the same composition as the previous phase. Histological analyses were performed on samples of immature leaves with and without calli at 0, 3, 15, 30, 60, 90 and 120 days in an induction medium, and on samples of the different types of calli and somatic embryos obtained during multiplication and differentiation. For this, the samples were fixed in FAA, dehydrated in an alcohol series and infiltrated in resin. Anatomical sections obtained on a microtome were stained with Toluidine Blue for structural characterization. At 60 days, analyses revealed the formation of callogenic masses in the vicinity of smaller vascular bundles. This multiplication approach allowed for the proliferation of the primary cell mass that evolved into new lineages of calli, especially the embryogenic yellowish nodular lineage, which originated somatic embryos. Additional histochemical analyses showed starch accumulation only in the adjacencies of areas undergoing intense cell division. The morpho-anatomic characterization allows the rapid identification of potential calli for the formation of somatic embryos from leaf tissues in macaw palm and promotes future investigations of the participation of vascular tissues in the events that precede somatic embryogenesis.

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