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      Genome size variation and karyotype diversity in eight taxa of Sorbus sensu stricto (Rosaceae) from China

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          Eight taxa of Sorbus Linnaeus, 1753 sensu stricto ( Rosaceae ) from China have been studied karyologically through chromosome counting, chromosomal measurement and karyotype symmetry. Genome size was also estimated by flow cytometry. Six taxa, S. amabilis Cheng ex T.T.Yu et K.C.Kuan, 1963, S. hupehensis var. paucijuga (D.K. Zang et P.C. Huang, 1992) L.T. Lu, 2000, S. koehneana C.K. Schneider, 1906, S. pohuashanensis (Hance, 1875) Hedlund, 1901, S. scalaris Koehne, 1913 and S. wilsoniana C.K. Schneider, 1906 are diploids with 2n = 34, whereas two taxa, S. filipes Handel-Mazzetti,1933 and S. ovalis McAllister, 2005 are tetraploid with 2n = 68. In general, the chromosome size is mainly small, and karyotypes are symmetrical with predominance of metacentric chromosomes. Genome size variation of diploids and tetraploids is 1.401 pg –1.676 pg and 2.674 pg –2.684 pg, respectively. Chromosome numbers of S. amabilis and S. hupehensis var. paucijuga , and karyotype and genome size of eight taxa studied are reported for the first time. This study emphasised the reliability of flow cytometry in genome size determination to infer ploidy levels in Chinese native Sorbus species.

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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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            Genome downsizing in polyploid plants

             I. LEITCH,  M Bennett (2004)
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              Two new nuclear isolation buffers for plant DNA flow cytometry: a test with 37 species.

              After the initial boom in the application of flow cytometry in plant sciences in the late 1980s and early 1990s, which was accompanied by development of many nuclear isolation buffers, only a few efforts were made to develop new buffer formulas. In this work, recent data on the performance of nuclear isolation buffers are utilized in order to develop new buffers, general purpose buffer (GPB) and woody plant buffer (WPB), for plant DNA flow cytometry. GPB and WPB were used to prepare samples for flow cytometric analysis of nuclear DNA content in a set of 37 plant species that included herbaceous and woody taxa with leaf tissues differing in structure and chemical composition. The following parameters of isolated nuclei were assessed: forward and side light scatter, propidium iodide fluorescence, coefficient of variation of DNA peaks, quantity of debris background, and the number of particles released from sample tissue. The nuclear genome size of 30 selected species was also estimated using the buffer that performed better for a given species. In unproblematic species, the use of both buffers resulted in high quality samples. The analysis of samples obtained with GPB usually resulted in histograms of DNA content with higher or similar resolution than those prepared with the WPB. In more recalcitrant tissues, such as those from woody plants, WPB performed better and GPB failed to provide acceptable results in some cases. Improved resolution of DNA content histograms in comparison with previously published buffers was achieved in most of the species analysed. WPB is a reliable buffer which is also suitable for the analysis of problematic tissues/species. Although GPB failed with some plant species, it provided high-quality DNA histograms in species from which nuclear suspensions are easy to prepare. The results indicate that even with a broad range of species, either GPB or WPB is suitable for preparation of high-quality suspensions of intact nuclei suitable for DNA flow cytometry.

                Author and article information

                Comp Cytogenet
                Comp Cytogenet
                Comparative Cytogenetics
                Pensoft Publishers
                20 May 2021
                : 15
                : 2
                : 137-148
                [1 ] Co-Innovation Center for Sustainable Forestry in Southern China, College of Biology and the Environment, Nanjing Forestry University, Nanjing, 210037, Jiangsu, China Nanjing Forestry University Nanjing China
                Author notes
                Corresponding author: Xin Chen ( chenxinzhou@ 123456hotmail.com )

                Academic editor: Marina Iovene

                Jiabao Li, Kailin Zhu, Qin Wang, Xin Chen

                This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                the Priority Academic Program Development of Jiangsu Higher Education Institutions, Jiangsu Province, China (PAPD)
                Research Article

                sorbus evolution, polyploid, flow cytometry, dna content


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