Vladislav Kolarčik

Endoreduplication is a process in which cells repeatedly undergo the S and G phases of the cell cycle without dividing, thereby increasing their ploidy level. Cells with different ploidy levels subsequently form tissues and organs, resulting in a condition called endopolyploidy. This phenomenon plays an important role in plant growth, development, and homeostasis and may also help compensate for adverse environmental conditions, representing one of the mechanisms of stress adaptation. Two radish cultivars, ‘Lada’ and ‘Ester’, were grown hydroponically and treated with 10 or 20 μM cadmium and UV-B irradiation. The level of endopolyploidization and its role in adaptation to abiotic stress were studied by flow cytometry. Stress intensity was evaluated by measuring fresh weight, assimilatory pigment content, and antioxidant enzyme activities. The experimental data confirmed that cadmium exposure represents a critical limiting factor for radish growth, as manifested by a significant reduction in biomass and decreased content of photosynthetic pigments. Induced abiotic stress did not significantly alter endopolyploidization in the petioles and leaves of either cultivar. In the storage hypocotyl of ‘Ester’, the degree of endopolyploidy decreased under 20 μM cadmium treatment, whereas the storage hypocotyl of ‘Lada’ remained relatively stable. The cultivars also differed in their stress response strategies. ‘Ester’ showed higher sensitivity to cadmium stress, accompanied by elevated SOD, GPOX, and APX activity, while ‘Lada’ exhibited higher CAT activity. UV-B irradiation alone caused significant changes only in ‘Ester’, where APX, GPOX, and CAT activities increased. However, the combined effect of cadmium and UV-B was more pronounced, particularly in the chlorophyll a/b ratio and antioxidant enzyme activities in both cultivars. The results indicate that UV-B acts more as a modulator of the physiological response to cadmium than as a primary stress factor. These findings suggest that the maintenance of endopolyploidy may be associated with greater tolerance to the combined action of cadmium and UV-B stress.

The funarioid moss species Physcomitrium eurystomum, which is threatened with extinction, was the subject of this study. The riparian habitat type of this species is often under the influence of contaminated water, and, therefore, we tested the influence of selected potentially toxic elements (PTEs), namely zinc and copper, on the development, physiological features, and survival of the species on two different accessions (German and Croatian). The results obtained showed the different resilience of the two accessions to the PTEs. Flow cytometry analyses revealed that the two accessions differ significantly in terms of genome size. However, the different amplitude of resilience to the tested PTEs, the divergence in physiological responses, and survival within two accessions of the same species are confirmed, as well as the dissimilarity of their genome size, likely associated with ploidy level difference and possibly distinct hybrid origin.

Caves represent a specific environment with a special microclimate and fauna adapted to it. However, we have still a restricted knowledge on soil fauna communities in an environments with a marked microclimate gradient at the interface between cave and surface habitats. In the present study, we investigated the community patterns of dominant soil microarthropod group, oribatid mites, and their relationship to environmental factors across the microclimate gradient along a transect with seven study sites from cold and wet cave entrance zone to warm and drier deciduous forest. The cold and wet sites showed low oribatid abundances and a high spatial clustering of individuals in comparison to the warm sites. The oribatid mites showed significantly higher abundance and species richness at warm forest sites. Indicator species analysis indicated specific cold-tolerant species that dominated at cold sites of the gradient, but which were absent at the warmest sites. Variance analysis clarified that community composition at sites were significantly driven by environmental factors: temperature, soil moisture, pH and C/N ratio. The study underlines the importance of ice cave entrances as sources of high α-diversity of soil mesofauna and thus the conservation priority of these valuable habitats.

The group of lesser dandelions (Taraxacum sect. Erythrosperma) is represented by more than 215 species growing in mostly xerothermic habitats throughout Europe. The only known species with sexual reproduction in this section is the diploid T. erythrospermum. It occurs in southern parts of Europe and reaches its northern limit in central Europe. In this study, we aimed at a detailed mapping of the species distribution in Slovakia in order to understand the spatial distribution at its northern range limits. We found that it is the most common xerothermous species in Slovakia, growing on various substrates such as limestone, dolomite, travertine, volcanic rocks and sands, while it is less common on brown soils and ruderal biotopes. It is a characteristic species of the class Festuco-Brometea with an altitudinal range extending from 120 to 650 m above sea level. We delimited the northern distribution and documented its highest occurrence at approximately ca 1500 m a.s.l. Two taxa, T. slovacum and T. punctatum, were described from the territory of Slovakia and we discuss their relationships to T. erythrospermum, with which T. slovacum is synonymised here for the first time. We also present new data on the genome size of T. erythrospermum in Slovakia, which range from 1.529 to 1.604 pg with a mean of 1.554 pg (± 0.024 SD), and provide chorological data on a remarkable morphological variant with grey-coloured achenes.

The remarkable species diversity of the genus Sorbus is a result of polyploidization and frequent hybridization between interacting species of different cytotypes. Moreover, hybridization is possible between several parental taxa. Gametophytic apomixis, which is common among polyploid Sorbus taxa, indicates the role of clonal reproduction in the evolutionary stabilization of hybridogeneous genotypes. The precise determination of the origin of seeds and their quantitative evaluation may elucidate inter-cytotype interactions, the potential role of mixed-cytotype populations in evolutionary success, and the long-term survival of some hybrid species. We investigated the reproduction modes of selected species of Sorbus in mixed-cytotype populations in eastern Slovakia, Central Europe. We determined the pollen quality, seed production rate, and the ploidy level of mature trees, as well as the origin of the embryo and endosperm in seeds of the stenoendemics S. amici-petri, S. dolomiticola, and S. hornadensis. The tetraploids S. amici-petri and S. hornadensis are characterized by regular and highly stainable pollen grains and reproduce predominantly via pseudogamous apomixis. In contrast, triploid S. dolomiticola usually has oval, heterogenous, and weakly stainable pollen grains, suggesting male meiotic irregularities. Although seeds originate via pseudogamous apomixis in S. dolomiticola as well, the ploidy level of sperm cells participating in the fertilization of central cells is usually determined by co-occurring species of different cytotypes. This suggests that maintaining mating partners is necessary for the long-term survival of a triploid species. We documented rare B_III hybrids and the residual sexuality in tetraploids. The distribution of seeds of meiotic and apomeiotic origins in S. amici-petri shows bimodal characteristics; however, genotypes with predominantly sexual seed types are rare. Reproduction modes documented in polyploid stenoendemics of Sorbus and inferred microevolutionary intercytotype relationships highlight the mixed-cytotype populations as the source of biodiversity in apomictic plant complexes. We suggest that conservation efforts should focus on maintaining the species and cytotypic diversity of Sorbus populations, especially when it comes to the conservation of triploid species.

The role of apomeiosis, parthenogenesis, and pseudogamy in the asexual reproduction of some plant groups has not been fully elucidated in relation to species diversification. Quantitative analyses of seed origin may help in gaining better understanding of intercytotypic interactions. Asexual reproduction associated with polyploidy and frequent hybridization plays a crucial role in the evolutionary history of the genus Crataegus in North America. In Europe, the genus represents a taxonomically complex and very difficult species group not often studied using a modern biosystematic approach. We investigated the reproduction pathways in mixed-cytotype populations of selected taxa of Crataegus in eastern Slovakia, Central Europe. The investigated accessions were characterized by seed production data and the ploidy level of mature plants as well as the embryo and endosperm tissues of their seeds determined via flow cytometry. Diploid and polyploid hawthorns reproduce successfully; they also produce high numbers of seeds. An exception is represented by an almost sterile triploid. Diploids reproduce sexually. Polyploids shift to asexual reproduction, but pseudogamy seems to be essential for regular seed development. In rare cases, fertilization of unreduced gametes occurs, which offers opportunity for the establishment of new polyploid cytotypes between diploid sexuals and polyploid asexuals. Opposite to sexual diploids, triploids are obligate, and tetraploids almost obligate apomicts. Apomixis is considered to help stabilize individual weakly differentiated polyploid microspecies. Pseudogamy is a common feature and usually leads to unbalanced maternal to paternal contribution in the endosperm of triploid accessions. Parental contribution to endosperm gene dosage is somehow relaxed in triploids. Our Crataegus plant system resembles reproduction in the diploids and polyploids of North American hawthorns. Our data provide support for the hypothesis that polyploidization, shifts in reproduction modes, and hybridization shape the genus diversity also in Central Europe.

Genome size is species-specific feature and commonly constant in an organism. In various plants, DNA content in cell nucleus is commonly increased in process of endoreplication, cellular-specific multiplication of DNA content without mitosis. This leads to the endopolyploidy, the presence of multiplied chromosome sets in a subset of cells. The relationship of endopolyploidy to species-specific genome size is rarely analysed and is not fully understood. While negative correlation between genome size and endopolyploidy level is supposed, this is species- and lineage-specific. In the present study, we shed light on this topic, exploring both genome size and endoreplication-induced DNA content variation in two pairs of morphologically similar species of Pulmonaria, P. obscura–P. officinalis and P. mollis–P. murinii. We aim (i) to characterize genome size and chromosome numbers in these species using cytogenetic, root-tip squashing and flow cytometry (FCM) techniques; (ii) to investigate the degree of endopolyploidy in various plant organs, including the root, stem, leaf, calyx and corolla using FCM; and (iii) to comprehensively characterize and compare the level of endopolyploidy and DNA content in various organs of all four species in relation to species systematic relationships and genome size variation. We have confirmed the diploid–dysploid nature of chromosome complements, and divergent genome sizes for Pulmonaria species: P. murinii with 2n = 2x = 14, 2.31 pg/2C, P. obscura 2n = 2x = 14, 2.69 pg/2C, P. officinalis 2n = 2x = 16, 2.96 pg/2C and P. mollis 2n = 2x = 18, 3.18 pg/2C. Endopolyploidy varies between species and organs, and we have documented 4C–8C in all four organs and up to 32C (64C) endopolyploid nuclei in stems at least in some species. Two species with lower genome sizes tend to have higher endopolyploidy levels than their closest relatives. Endoreplication-generated tissue-specific mean DNA content is increased and more balanced among species in all four organs compared to genome size. Our results argue for the narrow relationship between genome size and endopolyploidy in the present plant group within the genus Pulmonaria, and endopolyploidization seems to play a compensatory developmental role in organs of related morphologically similar species.

Carex pulicarisis considered an endangered species, and further losses are forecast under the influence of even moderate climate change. Local studies indicate that temporal declines inC. pulicarisabundance are positively correlated to decreases in precipitation and increases in air temperature. Determining ecological properties on larger scales than local ones can help develop effective protection programs for the species. We hypothesize that the local relationships observed betweenC. pulicarisabundance and precipitation, air temperature and soil properties will be confirmed in a spatially-oriented large-scale study performed in situ. Therefore, the present study takes a novel, large-scale integrated approach to (1) precisely characterize the ecological requirements ofC. pulicariswithin its eastern distribution range, and (2) determine the influence of its community type, soil properties and climatic conditions on its abundance. It was found thatC. pulicarisis not a dominant or codominant species in the studied phytocoenoses in the eastern distribution range. Five natural vegetation groups includingC. pulicaris, with significantly diverse species compositions, were resolved: well supported Estonian, Polish, Slovak and Radecz groups, and a weakly-supported Ambiguous group. The abundance ofC. pulicariswas found to be positively correlated with the composition of the geographically-diversified plant communities and atmospheric precipitation, and to be also negatively associated with latitude and soil pH. Although the species is adapted to a relatively wide range of soil types, such adaptation requires appropriate substrate moisture level and light conditions. The species prefers moist organic and mineral soils and grows on both acid and neutral medium, characterized by a narrow C:N ratio, with various amounts of digestible total P, Mg and N, and low levels of digestible K. Climate change, manifested by reduced rainfall, may be one of the most important predictors negatively affecting the occurrence ofC. pulicaris.