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      New chromosome counts and genome size estimates for 28 species of Taraxacum sect. Taraxacum

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      Comparative Cytogenetics

      Pensoft Publishers

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          Abstract

          The species-rich and widespread genus Taraxacum F. H. Wiggers, 1780 (Asteraceae subfamily Cichorioideae) is one of the most taxonomically complex plant genera in the world, mainly due to its combination of different sexual and asexual reproduction strategies. Polyploidy is usually confined to apomictic microspecies, varying from 3x to 6x (rarely 10x). In this study, we focused on Taraxacum sect. Taraxacum (= T. sect. Ruderalia; T. officinale group), i.e., the largest group within the genus. We counted chromosome numbers and measured the DNA content for species sampled in Central Europe, mainly in Czechia. The chromosome number of the 28 species (T. aberrans Hagendijk, Soest & Zevenbergen, 1974, T. atroviride Štěpánek & Trávníček, 2008, T. atrox Kirschner & Štěpánek, 1997, T. baeckiiforme Sahlin, 1971, T. chrysophaenum Railonsala, 1957, T. coartatum G.E. Haglund, 1942, T. corynodes G.E. Haglund, 1943, T. crassum H. Øllgaard & Trávníček, 2003, T. deltoidifrons H. Øllgaard, 2003, T. diastematicum Marklund, 1940, T. gesticulans H. Øllgaard, 1978, T. glossodon Sonck & H. Øllgaard, 1999, T. guttigestans H. Øllgaard in Kirschner & Štěpánek, 1992, T. huelphersianum G.E. Haglund, 1935, T. ingens Palmgren, 1910, T. jugiferum H. Øllgaard, 2003, T. laticordatum Marklund, 1938, T. lojoense H. Lindberg, 1944 (= T. debrayi Hagendijk, Soest & Zevenbergen, 1972, T. lippertianum Sahlin, 1979), T. lucidifrons Trávníček, ineditus, T. obtusifrons Marklund, 1938, T. ochrochlorum G.E. Haglund, 1942, T. ohlsenii G.E. Haglund, 1936, T. perdubium Trávníček, ineditus, T. praestabile Railonsala, 1962, T. sepulcrilobum Trávníček, ineditus, T. sertatum Kirschner, H. Øllgaard & Štěpánek, 1997, T. subhuelphersianum M.P. Christiansen, 1971, T. valens Marklund, 1938) is 2n = 3x = 24. The DNA content ranged from 2C = 2.60 pg (T. atrox) to 2C = 2.86 pg (T. perdubium), with an average value of 2C = 2.72 pg. Chromosome numbers are reported for the first time for 26 species (all but T. diastematicum and T. obtusifrons), and genome size estimates for 26 species are now published for the first time.

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          Most cited references 58

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          Plant DNA flow cytometry and estimation of nuclear genome size.

          DNA flow cytometry describes the use of flow cytometry for estimation of DNA quantity in cell nuclei. The method involves preparation of aqueous suspensions of intact nuclei whose DNA is stained using a DNA fluorochrome. The nuclei are classified according to their relative fluorescence intensity or DNA content. Because the sample preparation and analysis is convenient and rapid, DNA flow cytometry has become a popular method for ploidy screening, detection of mixoploidy and aneuploidy, cell cycle analysis, assessment of the degree of polysomaty, determination of reproductive pathway, and estimation of absolute DNA amount or genome size. While the former applications are relatively straightforward, estimation of absolute DNA amount requires special attention to possible errors in sample preparation and analysis. The article reviews current procedures for estimation of absolute DNA amounts in plants using flow cytometry, with special emphasis on preparation of nuclei suspensions, stoichiometric DNA staining and the use of DNA reference standards. In addition, methodological pitfalls encountered in estimation of intraspecific variation in genome size are discussed as well as problems linked to the use of DNA flow cytometry for fieldwork. Reliable estimation of absolute DNA amounts in plants using flow cytometry is not a trivial task. Although several well-proven protocols are available and some factors controlling the precision and reproducibility have been identified, several problems persist: (1) the need for fresh tissues complicates the transfer of samples from field to the laboratory and/or their storage; (2) the role of cytosolic compounds interfering with quantitative DNA staining is not well understood; and (3) the use of a set of internationally agreed DNA reference standards still remains an unrealized goal.
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            The origin, evolution and proposed stabilization of the terms 'genome size' and 'C-value' to describe nuclear DNA contents.

            Perusing the literature on nuclear 'genome size' shows that the term is not stabilized, but applied with different meanings. It is used for the DNA content of the complete chromosome complement (with chromosome number n), for which others use 'C-value', but also for the DNA content of the monoploid chromosome set only (with chromosome number x). Reconsideration of the terminology is required. Our purpose is to discuss the currently unstable usage of the terms 'genome size' and 'C-value', and to propose a new unified terminology which can describe nuclear DNA contents with ease and without ambiguity. We argue that there is a need to maintain the term genome size in a broad sense as a covering term, because it is widely understood, short and phonetically pleasing. Proposals are made for a unified and consensual terminology. In this, 'genome size' should mean the DNA content based on chromosome number x and n, and should be used mainly in a general sense. The necessary distinction of the kinds of genome sizes is made by the adjectives 'monoploid' and the neology 'holoploid'. 'Holoploid genome size' is a shortcut for the DNA content of the whole chromosome complement characteristic for the individual (and by generalization for the population, species, etc.) irrespective of the degree of generative polyploidy, aneuploidies, etc. This term was lacking in the terminology and is for reasons of linguistic consistency indispensable. The abbreviated terms for monoploid and holoploid genome size are, respectively, Cx-value and C-value. Quantitative data on genome size should always indicate the C-level by a numerical prefix, such as 1C, 1Cx, 2C, etc. The proposed conventions cover general fundamental aspects relating to genome size in plants and animals, but do not treat in detail cytogenetic particularities (e.g. haploids, hybrids, etc.) which will need minor extensions of the present scheme in a future paper.
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              The Chromosome Counts Database (CCDB) - a community resource of plant chromosome numbers.

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                Author and article information

                Journal
                Comparative Cytogenetics
                CCG
                Pensoft Publishers
                1993-078X
                1993-0771
                September 18 2018
                September 18 2018
                : 12
                : 3
                : 403-420
                Article
                10.3897/CompCytogen.v12i3.27307
                © 2018

                http://creativecommons.org/licenses/by/4.0/

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