## 4 Discussion
### Genetic Stability of Octaploids  
The octaploid regenerants obtained here seem to show genetic stability, which could be concluded based on the stable genome size (2C = 1.642 pg), high pollen viability seed setting and germination. The polyploidy seems to be passed to the next generation without significant losses in the genome as the progeny of octaploids manifest a doubled chromosome number (\(2n=8x=64\)). This is likely because they were obtained from a single callus cell (or cell group), not from chimeras which are usually obtained after treatment of the seedlings/seeds with colchicine [69]. In the latter case, the high frequency of mixoploidy and genetic instability of progeny is often detected, which is undesirable in breeding procedures [70; 71]. Maintenance of polyploid stability requires the development of mechanisms to control pairing and segregation of more than two homologous chromosomes during meiosis [15; 16; 72]. Meiosis in octaploid regenerants of _A. arenosa_ must be regular since pollen viability is high, reaching almost 97%, similar to tetraploid regenerants and initial plants. Furthermore, pollen grains size in octaploids did not vary significantly, which means that they were cytologically balanced (likely possessing constant chromosome number, \(1n=32\)). It seems that pollen of _A. arenosa_ is not very sensitive to both internal and external factors in this species, as in plants growing at heavy-metal polluted sites, male meiosis was almost not impaired by pollution, and pollen was also highly viable [73]. Such highly probable diploid-like chromosome pairings during octaploid meiosis, whose bivalents are selected randomly from eight homologs already in the first generation of regenerants, are amazing. In the synthetic autopolyloid _Physalis ixocarpa_, pollen viability was reduced almost by half (from above 90% in the diploid to 50-60% in the tetraploid), similar to somatic autotetraploid _Hylocereus_, although to a significantly lower extent (97% in the diploid vs. 86% in the tetraploid) [74; 75]. [PERSON] et al. (2012), based on the functional annotations of the _A. thaliana_ homologs, indicated candidate genes and processes (regulation of core transcription, epigenetic regulation, DNA repair, cell division and morphogenesis, chromosome synapsis and cohesion, homologous recombination, and chromosome segregation) that may have been important for compensatory adaptation of _A. arenosa_ to its genome-doubled state [15]. Similar or other unknown mechanisms may be responsible for such high genetic stability of obtained octaploids of _A. arenosa_.  
To sum up, we believe that the higher-level autopolyloids (now diploid, tetraploid, and octaploid cytotypes of _A. arenosa_ are available) are an excellent model for studying the increase in ploidy as a mechanism that does not restrict the persistence of neopolyloids in this species. Given the close relationship of the sequenced genome _A. thaliana_, it will be possible in the future to edit their genes, e.g., by PCR in these polyploid lines. This provides a route to generate polyploid mutants for improving the understanding of genome dosage effects in polyploid plants [76].