Modifications of DNA nucleobases are present in all forms of life. The purpose of these modifications in eukaryotic cells, however, is not always clear. Although the role of 5-methylcytosine (m⁵C) in epigenetic regulation and the maintenance of stability in plant genomes is becoming better understood, knowledge pertaining to the origin and function of oxidized nucleobases is still scarce. The formation of 5-hydroxymetylcytosine (hm⁵C) in plant genomes is especially debatable. DNA modifications, functioning as regulatory factors or serving as DNA injury markers, may have an effect on DNA structure and the interaction of genomic DNA with proteins. Thus, these modifications can influence plant development and adaptation to environmental stress. Here, for the first time, the changes in DNA global levels of m⁵C, hm⁵C, and 8-oxo-7,8-dihydroguanine (8-oxoG) measured by ELISA have been documented in recalcitrant embryonic axes subjected to desiccation and accelerated aging. We demonstrated that tissue desiccation induces a similar trend in changes in the global level of hm⁵C and 8-oxoG, which may suggest that they both originate from the activity of reactive oxygen species (ROS). Our study supports the premise that m⁵C can serve as a marker of plant tissue viability whereas oxidized nucleobases, although indicating a cellular redox state, cannot.

Instytut Dendrologii PAN w Kórniku - Institute of Dendrology PAS (Kórnik, Poland)

Silvicultural practices can alter forest genetic resources in unpredictable ways, thereby influencing the adaptive and evolutionary potential of forest populations. This is especially alarming in the case of species with more northern distribution centers, due to the lack of area that can be colonized further north. In this article, we studied the genetic diversity of the Scots pine seed tree stand in Poland, its natural regeneration, and two artificially established progeny plantations. The research aimed to determine whether the regeneration mode had affected the efficiency of the gene pool transmission from the maternal seed stand to its offspring. Using nuclear microsatellite markers we compared the parameters of genetic variation and allelic composition among the studied stands. The results showed that all stands represent a common genetic pool with slightly higher values of observed heterozygosity in the case of progeny plantations. Inbreeding was significant only in natural regeneration. All stands have gained and lost rare alleles compared to the maternal seed stand. Nevertheless, the analysis of population differentiation showed that the gene pool of the maternal stand had been transmitted more efficiently to the natural regeneration, though the difference was only minimal. Possible reasons for the differences in transmission efficiency between natural regeneration and artificially established progeny plantations mainly include variations in the number of mother trees and crossing patterns in different reproductive seasons. Furthermore, some individuals that grow in the studied progeny plantations may be natural regeneration of the neighboring stands. In light of the obtained results, we discuss the genetic considerations for establishing and using seeds from progeny plantations in Poland.

Key message: The core populations of the European white elm (Ulmus laevis Pall.) located in Poland maintained slightly higher level of genetic diversity compared to the peripheral populations of this species. Context: The most severe threat to elms is the loss of natural habitat under the pressures of agriculture and forestry as well as urbanization. The reductions in European white elm populations as well as populations of other elm species have also been caused by Dutch elm disease (DED). Previous studies have indicated a low level of genetic variation in Ulmus leavis Pall. However, in Poland, the genetic resources and demographic history of U. laevis populations remain poorly documented. Aims: The genetic resources of U. laevis in Poland were identified and characterized. Additionally, tests were performed to identify potential bottleneck signatures and effective population sizes of the examined populations. Methods: Polymorphism was analyzed using a set of six nuclear microsatellite markers (nSSRs) for 1672 individuals from 41 populations throughout the species range in Poland. Results: (1) A moderate level of genetic variation was found. (2) A low genetic differentiation and lack of population structuring were identified. (3) Evidence of reduction in population size was found as a consequence of severe, past bottlenecks. Conclusion: The loss of genetic diversity of U. laevis probably occurred in their refugia or shortly after the postglacial recolonization. This loss may have been affected by past DED pandemics similar to those seen at present.