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.

Aims Ectomycorrhizal fungi can improve poplar growth and tolerance to heavy metal stress, and may be useful during the afforestation and phytoremediation of polluted regions with poplar trees. In this study, we determined the effects of the symbiotic interaction between Populus × canescens trees and Paxillus involutus strains different in their tolerance to lead. Methods In vitro inoculated and non-inoculated plants were treated with 0.75 mM Pb(NO₃)₂. The root colonization rate of the two fungal strains, as well as their impacts on poplar health and lead accumulation were examined. Results Based on the colonization level, the roots were classified into one of three categories: non-mycorrhized, changed (ie, fungal cells were present on the root surface, but the Hartig net did not fully develop), and fully mycorrhized. The lead-tolerant P. involutus strain colonized roots better than the non-tolerant strain (ie, changed and fully mycorrhized roots). Moreover, plants inoculated with the tolerant fungal strain grew better than the control plants (217 % increase in dry weight over the controls), and accumulated lead in the roots and stems. Conclusions Inoculation of P. × canescens trees with a Pb-tolerant strain of P. involutus improves host plant growth and may increase Pb phytostabilization potential.

Somatic embryogenesis (SE) is an important method for the vegetative propagation of trees. SE is the developmental in vitro process in which embryos are produced from somatic cells. This method can be integrated with other biotechnological techniques, genomic breeding and cryopreservation, which enables commercial-scale sapling production of selected high-yielding genotypes in wood production combined with fast breeding cycles. The SE is potential tool to improve plant stock in comparison with seed orchards. It can be useful for ecologically and economically important species, such as Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), ensuring stable production in the era of climate change and biodiversity crisis. In this review, we summarize the current state of research on problems associated with somatic embryogenesis in P. abies and P. sylvestris.

The genus Juniperus (of the Cupressaceae family) is the second most prevalent group of conifers on Earth. Juniper species are widely dispersed in the Northern Hemisphere, in Europe and Asia, and in Africa and Central America. Juniper species are resistant to dry climates and can adapt to difficult environmental conditions. Most juniper species are important in both ecological and economic terms. However, today, many forests in which junipers occur are being reduced in size due to both natural causes (fires, for example) and human activity (uncontrolled exploitation of forests, etc.). Also, climate changes may have adversely affected the range of populations of different juniper species. For this reason, some juniper species are now categorized as rare or endangered, and require immediate protective action. Therefore, there is an urgent need to develop effective strategies for ex situ conservation, including reliable procedures for Juniperus sp. reproduction for future reintroduction and restoration programs. The conservation strategies used until now with traditional forestry techniques (seed propagation, rooted cuttings, grafting) have not been satisfactory in many cases. Thus, increasing attention is being paid to the possibilities offered by in vitro culture technology, which enables the conservation and mass clonal propagation of different coniferous tree species. In this mini-review, we summarize the current state of knowledge regarding the use of various methods of the propagation of selected Juniperus species, with a particular emphasis on in vitro culture techniques.