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Loureiro J., Trávníček P., Rauchová J., Urfus T., Vít P., Štech M., Castro S. & Suda J. (2010): The use of flow cytometry in the biosystematics, ecology and population biology of homoploid plants. – Preslia 82: 3–21.
Over the last decade there has been a tremendous increase in the use of flow cytometry (FCM) in studies on the biosystematics, ecology and population biology of vascular plants. Most studies, however, address questions related to differences in genome copy number, while the value of FCM for studying homoploid plant groups has long been underestimated. This review summarizes recent advances in taxonomic and ecological research on homoploid plants that were made using FCM. A fairly constant amount of nuclear DNA within each evolutionary entity together with the often large differences between species means that genome size is a useful character for taxonomic decision-making. Regardless of the number of chromosomes, genome size can be used to delimit taxa at various taxonomic levels, resolve complex low-level taxonomies, assess the frequency of interspecific hybridization or infer evolutionary relationships in homoploid plant groups. In plant ecology and evolutionary biology, variation in genome size has been used for prediction purposes because genome size is associated with several phenotypic, physiological and/or ecological characteristics. It is likely that in the future the use of FCM in studies on taxonomy, ecology and population biology of homoploid plants will increase both in scope and frequency. Flow cytometry alone, but especially in combination with other molecular and phenotypic approaches, promises advances in our understanding of the functional significance of variation in genome size in homoploid plants.

Krahulcová A. & Rotreková O. (2010): Use of flow cytometry in research on apomictic plants. – Preslia 82: 23–39.
This paper reviews recent use of flow cytometry in studies on apomictic plant taxa. The most of apomictic angiosperms are polyploid, often differing in ploidy level from their sexual counterparts within the agamic complex. Flow cytometry is widely used for screening the ploidy levels of mature plants and their seed generated both in the field and in experiments. Routine ploidy screening often accompanied by molecular markers distinguishing individual genotypes are used to reveal novel insights into the biosystematics and population biology of apomictic taxa. Apomixis (asexual seed formation) is mostly facultative, operating together with other less frequent reproductive pathways within the same individual. The diversity in modes of reproduction in apomicts is commonly reflected in the ploidy structure of their progeny in mixed-cytotype populations. Thus, flow cytometry facilitates the detection and quantification of particular progeny classes generated by different reproductive pathways. The specific embryo/endosperm ploidy ratios, typical of the different reproductive pathways, result from modifications of double fertilization in sexual/apomictic angiosperms. Thus, the reproductive origin of seed can be identified, including autonomous or pseudogamous apomixis, haploid parthenogenesis and sexual reproduction, involving either reduced or unreduced gametes. Collectively, flow cytometry has been used to address the following research topics: (i) assessing the variation in ploidy levels and genome sizes in agamic complexes, (ii) detection and quantification of different reproductive modes in facultative apomicts, (iii) elucidation of processes in populations with coexisting sexual and apomictic biotypes, (iv) evolution of agamic complexes, and (v) genetic basis of apomixis. The last topic is of paramount importance to crop breeding: the search for candidate gene(s) responsible for apomixis is the main objective of many research programmes. A list of the angiosperm taxa that could provide model systems for such research is provided.

Šmarda P. & Bureš P. (2010): Understanding intraspecific variation in genome size in plants. – Preslia 82: 41–61.
Intraspecific variation in genome size makes it possible to study ongoing processes of genome size evolution. Although there are over 200 papers on intraspecific variation in genome size, there is still limited understanding of this phenomenon, especially as many of these papers are based on weak methodology and therefore report biased or false evidence of the extent of intraspecific variation. In this paper the recent progress in understanding the spatio-temporal dynamics of intraspecific variation in genome size caused by the gradual accumulation of mutations is reviewed. The results of the case studies on Microseris douglasii, Zea mays, Silene latifolia, Hordeum spontaneum and Lolium hybrids, and in particular that on Festuca pallens, are discussed. The variation in genome size that occurs within species is caused mainly by differences in the content of repetitive DNA, in particular it is a consequence of the dynamics of transposable elements. Variation may be induced and maintained polytopically.We assume that it is probably more frequent in groups of young radiating species. Even in the initial stages, the variation in genome size generated within a population seems to be restricted by selection, which is also important in stabilizing genome size within species. The long-term persistence of the variation within a population and its further accumulation may be enhanced by gametes with different genome sizes, produced by the segregation of unequally sized homeologous chromosomes. Over large geographical scales and across contrasting environmental gradients, the distribution of genome sizes within species may be influenced by the nucleotype effect, with smaller genomes being more successful at higher latitudes and altitudes and under stressful conditions. However, the small differences in genome size within species seem generally to be of minor importance relative to other components of plant fitness that may be selectively favourable under particular environmental or habitat conditions. The processes generating variation in genome size may be associated with phenotypic variation. While the shift in the genome size of a population through selection enables adaptive evolution of genome size in a newly arising species, the spatio-temporal variation in genome size within an ancestral species allows for a rapid multiple genome size divergence of related species through random drift in genome size (founder effect, bottleneck effect) during range fragmentation, hybridization and/or polyploidization.

Temsch E. M., Greilhuber J. & Krisai R. (2010): Genome size in liverworts. – Preslia 82: 63–80.
Liverworts are poorly represented in the record of DNA C-values. Data for not more than nine species are reported in the literature. Here we present flow cytometric measurements of genome size for 32 foliose and 11 thallose species from 22 out of 83 families. The main method used in this study was flow cytometry using propidium iodide as the DNA stain. Feulgen densitometrywas applied as a supplementary method but it proved less suitable because the rigid cellwalls of liverwort tissue are resistant to maceration and apparently often inhibit the diffusion of reagents, which results in low estimates of DNA content. The precise or approximate number of chromosomes were counted, where possible. Among the thallose liverworts, the lowest 1C-value was recorded for Marchantia polymorpha (0.293 pg) and the highest for diploid Pellia epiphylla (7.401 pg). Haploid P. epiphylla (1C = 3.803 pg) had the largest genome among the haploid thalloid liverworts. Among the foliose liverworts, Lejeunea cavifolia with a value of 0.211 pg (1C) was ranked the lowest and Mylia taylorii, a haploid with 7.966 pg (1C) and a large amount of dense heterochromatin, concentrated in one big spherical chromocentre, the highest. This 38-fold variation covers the extremes of the whole sample and exceeds the ca 12-fold variation recorded in mosses (0.174–2.160 pg, 1C). This variation is nevertheless low compared to the 2000-fold interspecific variation found in angiosperms. Several instances of intraspecific variation in DNA ploidy (x and 2x) were found – in Radula complanata, Pellia epiphylla and Metzgeria furcata. In Lophocolea heterophylla, accessions differed 3.37-fold in C-value at haploid chromosome number. This points to cryptic taxonomic differentiation and warns against premature statements about ploidy levels based only on DNA measurements. Significant intraspecific intraploidal variation in C-value was also observed in certain instances. In Frullania dilatata, female plants with two large heterochromatic sex-chromosomes have a 1.35-fold higher C-value than male plants with only one sex chromosome. In most other cases of intraspecific variation the role of sex differences remains to be clarified.

Kubešová M., Moravcová L., Suda J., Jarošík V. & Pyšek P. (2010): Naturalized plants have smaller genomes than their non-invading relatives: a flow cytometric analysis of the Czech alien flora. – Preslia 82: 81–96.
Genome size has been suggested as one of the traits associated with invasiveness of plant species. To provide a quantitative insight into the role of this trait, we estimated nuclearDNAcontent in 93 alien species naturalized in the Czech Republic, belonging to 32 families, by using flow cytometry, and compared it with the values reported for non-invading congeneric and confamilial species from the Plant DNA C-values database. Species naturalized in the Czech Republic have significantly smaller genomes than their congeners not known to be naturalized or invasive in any part of the world. This trend is supported at the family level: alien species naturalized in the Czech flora have on average a smaller genome than is the mean value for non-invading confamilials. Moreover, naturalized and non-invading species clearly differed in the frequency of five genome size categories; this difference was mainly due to very small genomes prevailing and intermediate to very large genomes underrepresented in the former group. Our results provide the first quantitative support for association of genome size with invasiveness, based on a large set of alien species across a number of plant families. However, there was no difference in the genome size of invasive species compared to naturalized but non-invasive. This suggests that small genome size provides alien plants with an advantage already at the stage of naturalization and need not be necessarily associated with the final stage of the process, i.e. invasion.

Suda J., Trávníček P., Mandák B. & Berchová-Bímová K. (2010): Genome size as a marker for identifying the invasive alien taxa in Fallopia section Reynoutria. – Preslia 82: 97–106.
DAPI and propidium iodide flow cytometry were used to determine the variation in genome size in 166 samples and of all taxa and ploidy levels of Fallopia section Reynoutria (knotweeds) recorded in the Czech Republic. Significant differences were detected in the amount of nuclear DNA, associated with the ploidy levels and taxonomic identity of the material. At each ploidy level, F. sachalinensis showed the lowest and F. japonica the highest fluorescence intensities. The fluorescence values for the hybridogenous F. ×bohemica were located in-between these two levels. In most cases, there was at least a four-percent gap in fluorescence values between the nearest neighbours belonging to a different taxon. Intraspecific variation in genome size was very low in all taxa except hexaploid F. ×bohemica; this could be due to the complex evolutionary history of this taxon. Our results indicate that the amount of nuclear DNA can be used as a reliable marker for the identification of homoploid knotweed species and their hybrids. Different evolutionary pathways for the origin of high polyploids and/or hybridogenous taxa are proposed based on genome size.

Šafářová L. & Duchoslav M. (2010): Cytotype distribution in mixed populations of polyploid Allium oleraceum measured at a microgeographic scale. – Preslia 82: 107–126.
Despite the substantial knowledge of the variation in cytotypes at large spatial scales for many plants, little is known about the rates at which novel cytotypes arise or the frequencies and distributions of cytotypes at local spatial scales. The frequency distribution, local spatial structure, and role of habitat differentiation of tetra-, penta- and hexaploid cytotypes of the bulbous geophyte Allium oleraceum were assessed in 21 populations sampled in the Czech Republic. The ploidy levels determined by flow cytometry confirmed that there was a mixture consisting of two or three cytotypes (i.e. 4x+5x, 4x+6x, 5x+6x, 4x+5x+6x). In addition, mixtures of cytotypes were found at sites previously considered to be cytotype-homogeneous. At all sites previously found to contain a mixture of two cytotypes, no plants with the third ploidy level were found. Although the relative frequencies of cytotypes varied considerably both among and within populations, mixed populations consisting of tetra- and hexaploids were usually dominated by tetraploids. This suggests that there are secondary contacts among cytotypes but there is little gene flow among them except for the rare formation of hexaploids in tetraploid populations. Cytotypes were not randomly distributed over the study area but were spatially segregated at either 47.6% or 61.9% of the sites investigated, depending on the statistical test (Mantel test or average distance test) used. When the composition of habitats at each of the sites is taken into account, cytotypes were more frequently spatially segregated at sites with a heterogeneous environment than a homogeneous environment. This implies that the cytotypes are ecologically differentiated. The frequent co-occurrence of cytotypes, with or without significant spatial segregation, at many sites with heterogeneous or homogeneous environments, however, suggests that niche differentiation alone is probably ineffective in determining co-occurrence. It is supposed that the prevailing vegetative reproduction associated with local dispersal, a high population density of the species in a landscape, and non-equilibrial processes influencing the establishment and extinction of A. oleraceum populations can also support the local co-occurrence of cytotypes.

Dušková E., Kolář F., Sklenář P., Rauchová J., Kubešová M., Fér T., Suda J. & Marhold K. (2010): Genome size correlates with growth form, habitat and phylogeny in the Andean genus Lasiocephalus (Asteraceae). – Preslia 82: 127–148.
Variation in genome size in a particular taxonomic group can reflect different evolutionary processes including polyploidy, hybridization and natural selection but also neutral evolution. Using flow cytometry, karyology, ITS sequencing and field surveys, the causes of variation in genome size in the ecologically and morphologically diverse high-Andean genus Lasiocephalus (Asteraceae, Senecioneae) were examined. There was a 1.64-fold variation in holoploid genome size (C-values) among 189 samples belonging to 20 taxa. The most distinct was a group of plants with large genomes corresponding to DNA triploids. Disregarding the DNA triploids, the remaining samples exhibited a pronounced (up to 1.32-fold) and rather continuous variation. Plants with the smallest genomes most likely represent intergeneric hybrids with the closely related and sympatric Culcitium nivale, which has a smaller genome than Lasiocephalus. The variation in genome size in samples of diploid Lasiocephalus was strongly correlated with several environmental and life history traits (altitude, habitat and growth form). However, all these factors, as well as genome size itself, were correlated with phylogeny (main split into the so-called ‘forest’ and ‘páramo’ clades), which most probably represents the true cause of the differentiation in intrageneric genome size. In contrast, relationships between genome size and phylogeny were not apparent at lower divergence levels. Instead, here we suggest that ecological conditions have played a role in driving shifts in genome size between closely related species inhabiting different environments. Collectively, this study demonstrates that various evolutionary forces and processes have shaped the variation in genome size and indicates that there is a need for multi-approach analyses when searching for the causes and consequences of changes in genome size.

Trávníček P., Eliášová A. & Suda J. (2010): The distribution of cytotypes of Vicia cracca in Central Europe: the changes that have occurred over the last four decades. – Preslia 82: 149–163.
The formation and maintenance of polyploids (via the development of various reproductive barriers) rank among the central questions of studies on polyploid evolution. However, the long time scale of most evolutionary processes makes the study of the dynamics of diploid-polyploid groups difficult. A suitable candidate for a targeted comparative study is Vicia cracca (Fabaceae), which in the late 1960s was subjected to a detailed cytotype screening in Central Europe. Re-sampling the original localities offers a unique opportunity to assess changes in the ploidy structure of the populations, which should reflect the cumulative effect of all the evolutionary forces acting on the plants. Using flow cytometry, the DNA ploidy levels of more than 6,500 individuals of V. cracca collected at 257 localities in Austria, the Czech Republic, Germany and the Slovak Republic were estimated. Three different cytotypes (2x, 3x and 4x) were detected. While tetraploids predominated in the western part of the area investigated (179 populations), the diploids had a more easterly distribution (62 populations). There is a secondary zone of cytotype contact near the boundary between the Czech and Slovak Republics. Sixteen populations (~6%) consisted of a mixture of 2x and 4x cytotypes. Triploids are very rare; only seven individuals were found in two otherwise diploid populations, indicating the existence of breeding barriers between diploids and tetraploids. The distribution of cytotypes is similar to that determined four decades ago using chromosome counts. Nevertheless, there are some discrepancies, namely the current absence of: (i) the diploid cytotype in southern Bohemia and (ii) the altitudinal segregation in the distribution of cytotypes, including two formerly recognized chromosomal races of diploids, perhaps a result of more representative sampling. Identical monoploid genome sizes (1Cx-values) of both the majority ploidy levels support an autopolyploid origin of the tetraploids.

Dúbravková D., Chytrý M., Willner W., Illyés E., Janišová M. & Kállayné Szerényi J. (2010): Dry grasslands in the Western Carpathians and the northern Pannonian Basin: a numerical classification. – Preslia 82: 165–221.
A syntaxonomical revision of dry grasslands of the alliances Bromo pannonici-Festucion pallentis, Festucion valesiacae and Koelerio-Phleion phleoidis (class Festuco-Brometea) in the natural biogeographical region of the Western Carpathians and northern Pannonian Basin is presented. A geographically stratified data set of 2686 relevés from the south-eastern Czech Republic, northeastern Austria, Slovakia and northern Hungary was divided into 25 clusters using a modified TWINSPAN algorithm. The proposed classification simplifies and unifies the previous syntaxonomical systems, which differ in these four countries. Main environmental gradients responsible for variation in species composition of theses grasslands were revealed by detrended correspondence analysis and interpreted using indicator values. The major pattern of variation reflects soil nutrient availability and moisture, which are negatively correlated with soil reaction.

Dudová L., Hájek M. & Hájková P. (2010): The origin and vegetation development of the Rejvíz pine bog and the history of the surrounding landscape during the Holocene. – Preslia 82: 223–246.
The Rejvíz bog is an extensive mire complex in Central Europe, with up to 7 m deep sediments and two natural lakes. Recent vegetation is one of the best preserved examples of Pinus uncinata subsp. uliginosa (syn. P. rotundata) bog woodland in Central Europe. The origin and development of the mire and changes in the surrounding landscape vegetation are reconstructed using sediment stratigraphy, radiocarbon dating, pollen analysis and plant-macrofossils analysis, with particular emphasis on the processes that resulted in the origin of Rejvíz bog and on pine woodland dynamics. Based on identified species the water level changes were reconstructed. The sediment started to accumulate more than 9000 years ago at an open mixed-woodland spring with Dichodontium palustre. Later, poor fen vegetation with sedges and horsetails developed. Around 6170 cal. yr BC the fen became inundated for 2000 years and (semi)aquatic vegetation thrived. Next step in the succession followed a decline in water level which resulted in the development of drier oligothrophic vegetationwith a high representation of pine and dwarf shrubs. After ca 1020 cal. yr BC the mire became the bog it is now. Three wooded stages appeared in both the minerotrophic and ombrotrophic developmental phases: before 6720 cal. yr BC, during ca 1960–1020 cal. yr BC and recently. The vegetation in the surrounding landscape developed without marked human interventions up till ca the last six or five centuries, when deforestation and later settlement took place. Comparison with published data from the Góry Bystrzyckie/Orlické hory Mts suggests that not only regional, but also local vegetation changed in a similar way across the middle-altitude eastern Sudetes, following oscillations in climate rather than local changes in mire water regime.

Csiky J., Mesterházy A., Szalontai B. & Pótóné Oláh E. (2010): A morphological study of Ceratophyllum tanaiticum, a species new to the flora of Hungary. – Preslia 82: 247–259.
Ceratophyllum tanaiticum Sapjegin, a species new to the flora of Hungary, was discovered at two localities in the Hungarian part of the Drava Plain in 2008. These are the westernmost, disjunct localities of this Pontic-Caspian endemic species. For characterization of the Hungarian specimens, nine morphological features of nine Ceratophyllum taxa were used in PCA, CVA analyses and UPGMA classification. In these analyses Hungarian and other C. tanaiticum samples always formed a cluster distinct from other Ceratophyllum taxa. These results confirm an earlier concept in which the character peduncle length contributed the highest loading value for separating C. tanaiticum from other 3–4 leaf-ordered species. Microscopic morphological features, including the number of longitudinally arranged lacunae in one row of parenchymatic tissue between the first and the second dichotomic branching, the length of the sequence between the first and second branching of leaves; number, morphology and width of bracts under the fruit of fresh Hungarian material are identified as new characters for C. tanaiticum, C. submersum and C. demersum.

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