Abstract
Telomeres i.e., termini of the eukaryotic chromosomes protect chromosomes during DNA replication. Shortening of telomeres, either due to stress or ageing is related to replicative cellular senescence. There is little information on the effect of biotechnological methods, such as tissue culture via somatic embryogenesis (SE) or cryopreservation on plant telomeres, even if these techniques are widely applied. The aim of the present study was to examine telomeres of Norway spruce (Picea abies (L.) Karst.) during SE initiation, proliferation, embryo maturation, and cryopreservation to reveal potential ageing or stress-related effects that could explain variation observed at SE process. Altogether, 33 genotypes from 25 families were studied. SE initiation containing several stress factors cause telomere shortening in Norway spruce. Following initiation, the telomere length of the embryogenic tissues (ETs) and embryos produced remains unchanged up to one year of culture, with remarkable genotypic variation. Being prolonged in vitro culture can, however, shorten the telomeres and should be avoided. This is achieved by successful cryopreservation treatment preserving telomere length. Somatic embryo production capacity of the ETs was observed to vary a lot not only among the genotypes, but also from one timepoint to another. No connection between embryo production and telomere length was found, so this variation remains unexplained.
Highlights
Eukaryotic chromosomes are formed of a single DNA molecule, which terminates in specialized heterochromatin called telomeres [1]
There were significant differences in the somatic embryogenesis (SE) initiation rate among the studied families, and in the somatic embryo production capacity of the studied genotypes and timepoints, and the connections to these observed differences to variation in telomeric repeat length are discussed
To test somatic embryo production capacity of the different lines at various time points, the filter maturation method modified from [42] and described by Varis et al [28] was applied: About 180 (±20) mg of embryogenic tissues (ETs) was mixed in 3 mL liquid mLM without plant growth regulators (PGR), and the suspension was poured onto paper filter (Whatman #2) placed in the Buchner funnel
Summary
Eukaryotic chromosomes are formed of a single DNA molecule, which terminates in specialized heterochromatin called telomeres [1]. Telomeres consist of repeated DNA sequence that in most of the plant species is a heptanucleotide (TTTAGGG)n. The function of telomeres is to protect chromosomes from degradation and fusion during DNA replication, and in cell divisions, they are especially important for chromosome organization [1]. Cells’ conventional DNA polymerase is, not able to fully replicate the linear termini of the chromosomes i.e., telomeres, but they are maintained by a specific enzyme, telomerase. If only one or a subset of telomeres is shortened below a critical length, replicative cellular senescence may be triggered by DNA damage response (DDR) [2]. In DDR, cell’s own DNA repair machinery misidentifies the natural ends of the chromosomes as damaged DNA and this can further lead to either programmed cell death or in irreversibly arrested proliferation even if the cells stay alive [2]
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