Somatic embryogenesis is induced commonly using the auxin:
Somatic embryogenesis induction most frequently relies on auxin 2,4 dichlorophenoxyacetic acid 2,4-D applied at 0.5 to 10 mg per L because this synthetic phenoxy auxin resists degradation by IAA oxidases maintains prolonged auxinic signaling. High 2,4-D imposes stress and auxin response causing differentiated somatic cells to re-enter cell division and acquire totipotency through global epigenetic reprogramming involving DNA demethylation histone acetylation and activation of chromatin remodeling factors. It stimulates expression of embryogenic competence markers SERK1 glutathione S transferase and ABA responsive genes elevating endogenous auxin via upregulation of YUCCA genes. Auxin response factors ARF5 LEAFY COTYLEDON2 are induced initiating embryonic program while suppressing photosynthetic leaf identity genes. Persistent high concentration inhibits progression beyond globular stage because polar auxin transport via PIN1 required for bilateral symmetry cannot establish; therefore after competence achievement cultures are transferred to low auxin or hormone free medium often supplemented with ABA to permit maturation through heart torpedo cotyledonary stages. IAA NAA IBA are weaker inducers used for embryo maintenance rather than induction.
Ref: Dudits et al., J Exp Bot 2011 2,4-D embryogenesis; NCBI Book somatic embryogenesis.