Abstract
The effects of auxins 2,4-D (2,4-dichlorophenoxyacetic acid), NAA (1-naphthaleneacetic acid) or picloram (4-amino-3,5,6-trichloropicolinic acid; 9 µM) and cytokinin BA (benzyloadenine; 4.5 µM) applied in the early stages of somatic embryogenesis (SE) on specific stages of SE in Picea abies and P. omorika were investigated. The highest SE initiation frequency was obtained after 2,4-D application in P. omorika (22.00%) and picloram application in P. abies (10.48%). NAA treatment significantly promoted embryogenic tissue (ET) proliferation in P. abies, while 2,4-D treatment reduced it. This reduction was related to the oxidative stress level, which was lower with the presence of NAA in the proliferation medium and higher with the presence of 2,4-D. The reduced oxidative stress level after NAA treatment suggests that hydrogen peroxide (H2O2) acts as a signalling molecule and promotes ET proliferation. NAA and picloram in the proliferation medium decreased the further production and maturation of P. omorika somatic embryos compared with that under 2,4-D. The quality of the germinated P. abies embryos and their development into plantlets depended on the auxin type and were the highest in NAA-originated embryos. These results show that different auxin types can generate different physiological responses in plant materials during SE in both spruce species.
Highlights
Somatic embryogenesis (SE) is one of the most efficient in vitro regeneration systems for some coniferous tree species [1]
Embryonic tissue initiation from mature zygotic embryos was obtained for both spruce species regardless of the auxin used (Table 1, Figure 1A,B and Figure 2A,B), and the auxin used had no significant effect on embryogenic tissue (ET) initiation in either species (P. abies: Pχ2 = 1.8114, DF = 2 < 0.05 and P. omorika Pχ2 = 4.7474, DF = 2 < 0.05)
The highest percentage of explants that produced embryogenic masses was observed in Picea abies on the medium supplemented with picloram (10.48%, 24/229), whereas in P. omorika, it was observed on the medium with 2,4-D (22.00%, 55/250)
Summary
Somatic embryogenesis (SE) is one of the most efficient in vitro regeneration systems for some coniferous tree species [1]. Together with cryopreservation and genetic transformation techniques, it represents a modern biotechnological tool for the mass vegetative propagation of economically and ecologically important trees. The process of SE in conifers is very complex and includes many steps [2]. In the SE process, embryos develop from somatic cells without fertilization. The obtained embryos (so-called somatic embryos) have the same genotype as the somatic cells, and they strongly resemble zygotic embryos in seeds. Developed somatic embryos have a typical bipolar structure with a shoot and root apices and can germinate and grow into somatic seedlings
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