LEAFY COTYLEDON2-mediated control of the endogenous hormone content: implications for the induction of somatic embryogenesis in Arabidopsis

The overexpression of LEAFY COTYLEDON2 (LEC2) in Arabidopsis, results in the induction of somatic embryogenesis (SE) in an auxin-free environment and the stimulation of auxin biosynthesis was postulated as being involved in this response. To gain further insight into the hormone-related functions of LEC2 in SE, the effect of LEC2 overexpression on the hormone content in Arabidopsis plants and in vitro cultured explants was analysed. In addition to indole-3-acetic acid (IAA) and cytokinins (CKs), which are hormones that play a key role in plant development, the stress-related hormones, abscisic acid (ABA) and salicylic acid (SA), which are involved in the stress response that is related to SE-induction, were analysed. Together with the observations that LEC2 activity can compensate for the auxin treatment required for SE induction (Ledwoń and Gaj in Plant Tissue Cell Org Cult 28:1677–1688, 2009) and LEC2 may control auxin biosynthesis pathway during SE induction (Wójcikowska et al. in Planta 238:425–440, 2013), a significant increase in the IAA content in response to LEC2 overexpression found in the present study supply further evidence that LEC2-controlled auxin biosynthesis may be involved in the mechanism that triggers embryogenic development in somatic cells. Moreover, LEC2-controlled SE induction was shown to be associated with a decrease in the total content of CKs and an accumulation of some specific CK types, including isopentenyl-adenin and cis-zeatin. Additionally, an increase in SA and a decrease in ABA content were also found to be related to LEC2 activity in embryogenically induced tissue. The obtained results provide further proof of the close link between LEC2 and the establishment of the hormonal environment that is required for the promotion of SE.