Somatic embryogenesis (SE) in conifers is governed by a complex network of hormonal metabolic and signaling pathways. Changes in the patterns and concentrations of endogenous phytohormones including auxins, cytokinins (CKs), abscisic acid (ABA), jasmonates, and salicylic acid (SA) were analyzed in the course of SE in Norway spruce (Picea abies). Taking advantage of advanced HPLC-ESIMS/MS, as yet the most comprehensive overview of the plant hormonome in somatic embryos was provided here that revealed substantial variations in the levels of particular phytohormone classes during proliferation, maturation, desiccation, and germination. The peak in concentration of endogenous ABA and its inactive catabolite, dihydrophaseic acid, at the start of maturation, reflected the presence of exogenous ABA in the medium and showed its efficient perception and deactivation by the embryos as a prerequisite for their further development. The concentration maxima at maturation were also shown for most auxins, both indole and non-indole, suggesting their role in embryo polarization. For the first time, endogenous jasmonates are reported in conifer somatic embryos reaching their highest levels at germination. The involvement of some other phytohormone derivatives such as the non-indole auxin phenylacetic acid, cis-zeatin- and dihydrozeatin-type CKs, and SA in the process of SE was demonstrated here for the first time as well. The aforementioned data together with substantial quantitative and qualitative changes in concentrations of individual CK forms during SE indicated potential correlations between endogenous phytohormone profiles and particular developmental stages of somatic embryos.
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