Morphoanotomical aspects of auxin herbicides-induced somatic embryogenesis in Euterpe edulis Martius, a symbol and threatened species of the Atlantic Forest

The palm Euterpe edulis presents primary meristematic growth without sprouting at the base, which prevents conventional vegetative propagation. Here, we assessed the effect of the herbicides 2,4-D and picloram on somatic embryogenesis as an alternative means for propagating and in vitro conservation of pro-embryogenic cultures of E. edulis, as their seeds are recalcitrant. Embryos could be effectively induced with 2,4-D (159.42 mu mol L-1) and PIC (300 mu mol L-1), totaling 44.33 and 76.33 embryos, respectively. Moreover, proembryos, embryogenic clusters, and somatic embryos were clearly visible. Embryogenic and meristematic cells presented marked staining of the cytoplasm, spherical shape of the cells and nucleus, and rapidly dividing nucleoli. Maturation of explants induced with 2,4-D and PIC was improved by adding 2iP (12.3 mu mol L-1), NAA (0.6 mu mol L-1), and AC (0.3 g L-1). During germination, BAP (1 mu mol L-1) and GA(3) (0.5 mu mol L-1) promoted primary root protrusion and emergence of the shoot. In summary, PIC (300 mu mol L-1) is suggested for embryogenic induction of E. edulis calli, and medium containing 2iP, NAA, and AC is suggested for maturation. Finally, medium containing BAP and GA(3) without an auxin pulse favors the conversion of E. edulis somatic embryos into plants.