Profiles of Endogenous Phytohormones Over the Course of Norway Spruce Somatic Embryogenesis

Abstract

Conifer somatic embryogenesis (SE) is a process driven by exogenously supplied plant growth regulators (PGRs). Exogenous PGRs and endogenous phytohormones trigger particular ontogenetic events. Complex mechanisms involving a number of endogenous phytohormones control the differentiation of cells and tissues, as well as the establishment of structures and organs. Most of the mechanisms and hormonal functions in the SE of conifers have not yet been described. With the aim to better understand these mechanisms, we provided detailed analysis of the spectrum of endogenous phytohormones over the course of SE in Norway spruce (Picea abies). Concentrations of endogenous phytohormones including auxins, cytokinins (CKs), abscisic acid (ABA), jasmonates, and salicylic acid (SA) in somatic P. abies embryos were analyzed by HPLC-ESI-MS/MS. The results revealed that the concentrations of particular phytohormone classes varied substantially between proliferation, maturation, desiccation, and germination. Endogenous ABA showed a maximum concentration at the maturation stage, which reflected the presence of exogenous ABA in the medium and demonstrated its efficient perception by the embryos as a prerequisite for their further development. Auxins also had concentration maxima at the maturation stage, suggesting a role in embryo polarization. Endogenous jasmonates were detected in conifer somatic embryos for the first time, and reached maxima at germination. According to our knowledge, we have presented evidence for the involvement of the non-indole auxin phenylacetic acid, cis-zeatin- and dihydrozeatin-type CKs and SA in SE for the first time. The presented results represent the currently most comprehensive overview of plant hormone levels in embryos throughout the whole process of conifer SE. The differences in concentrations of various classes of phytohormones over the proliferation, maturation, desiccation, and germination in somatic P. abies embryos clearly indicate correlations between endogenous phytohormone profiles and particular developmental stages of the SE of conifers.

Temperature and Water Availability During Maturation Affect the Cytokinins and Auxins Profile of Radiata Pine Somatic Embryos

“…However, up to know a deep analysis of endogenous cytokinins and IAA concentration in SE process in pines has not been determined. In this sense, and as it has been described previously, IAA and other phytohormones have an important role in embryo differentiation events (Silveira et al, 2004; Vondrakova et al, 2018); thus, a better understanding of the phytohormone profile in somatic embryos under different environmental conditions could enable us to manipulate this stage of SE to increase its efficiency. Taking into account all the above mentioned studies, the main objective of this study was the evaluation of how the environment of cultures (gellan gum concentration and temperature) along maturation stage affects the success of radiata pine SE processes as well as to analyze its effect in CK and IAA endogenous levels.…”

New Approaches to Optimize Somatic Embryogenesis in Maritime Pine

“…Although in maritime pine differential WOX2 expression between embryogenic and non-embryogenic cells has not been reported, in our work WOX2 and LEC1 expression was detected in both EM morphotypes, suggesting their embryogenic identity (Figure 6). Then, differences in maturation capability may be due to other factors implicated in the downregulation of both genes along the maturation process, such as other hormone contents as has been reported in a recent study in Norway spruce (Vondrakova et al, 2018), or may be regulated by another genes related with embryo development.…”

Cytological, Biochemical and Molecular Events of the Embryogenic State in Douglas-fir (Pseudotsuga menziesii [Mirb.])

“…Detected concentrations of isoprenoid CKs (largely cis Z- and iP-types) were relatively low, similar to those of BA hydroxylated derivatives. cis Z-type CKs also predominate throughout Norway spruce somatic embryogenesis according to Vondráková et al (2018). Distinct changes in levels of three isoprenoid CK forms—iP, its riboside and cis/trans Z—have been observed during growth of EMs in hybrid larch (Jourdain et al, 1997).…”

“…Molecular data were complemented with morphological and histo-cytological, biological and biochemical analyses. We have also quantified endogenous phytohormones-auxin, ABA and CKs-with known importance in the control of cell proliferation and differentiation during somatic embryogenesis in conifers (Vondráková et al, 2018).…”