Chronological age, changes in DNA methylation, and endogenous hormone levels of explants promote somatic embryogenesis of Euterpe edulis Martius

Euterpe edulis Martius is an endangered palm tree native to the Atlantic Forest. As it propagates only with seeds and does not tiller, the tree dies after its highly appreciated palm heart is harvested. In this study, we analyzed the embryogenic response of E. edulis with respect to maturity of the explant and concentration of picloram, an auxin mimetic. Immature fruits were harvested, and their seeds were extracted and germinated in vitro . After 2, 4, 6, and 8 months, the aerial parts of normal seedlings were excised and stem segments were used to induce somatic embryogenesis in the presence of 100, 125, 150, 175, and 200 µM picloram. The number of proembryos, induction rate, explant mass, oxidation, global DNA methylation, 1-aminocyclopropane-1-carboxylic acid, proline, polyamines, and ultrastructural analysis of cells were assessed. Six-month-old seedling explants achieved the highest number of proembryos and embryogenic induction rate at most picloram concentrations, as well as the highest 1-aminocyclopropane-1-carboxylic acid content, but lowest spermine and putrescine levels. Explants with somatic embryos exhibited lower DNA methylation levels than non-embryogenic calli. Proline content was highest in stem segments of younger seedlings (2-month-old). Despite being asynchronous, maturation with 5 µM abscisic acid was achieved. Therefore, 6-month-old E. edulis seedlings supplemented with 200 µM picloram could be used for ex situ conservation of this endangered species. Key message Six-month-old seedlings of the palm Euterpe edulis are the best source of explants for in vitro germination of this endangered species and, therefore, may contribute to its conservation.