ORIGINAL ARTICLE Most organs of sugar-beet (Beta vulgaris L.) plants at the vegetative and reproductive stages of development are polysomatic Ewelina Lukaszewska Æ Elwira Sliwinska Received: 16 October 2006 / Accepted: 21 February 2007 / Published online: 14 March 2007 Ó Springer-Verlag 2007 Abstract Polysomaty was studied using flow cytometry in different organs of diploid, triploid and tetraploid sugar- beet (Beta vulgaris L.) plants, in the first (at harvest) and the second (at the height of the blooming period) year of development. Of the organs/parts of organs of the vegeta- tive plant that developed during the first year, only the leaf lamina did not contain endopolyploid cells; in all others, one to three endocycles had occurred. The second-year seed-crop plant was also highly polysomatic; even in reproductive organs such as the flower and pericarp the endopolyploid cells were present (up to 8C and 32C, respectively). At this stage of development no endocycles occurred in the leaf lamina, flower bract, and inflorescence bract. The parts of the plant with no endopolyploid cells are recommended for ploidy estimation, and as a material suitable for micropropagation and genetic manipulations. Endoreduplication, up to 32C (64Cx), was organ-specific and correlated negatively with plant ploidy. The highest mean C-value, over 7, was in the diploid, in the basal part of the oldest leaf petiole in the first-year plant, and in the storage parenchyma of the root in the second-year seed- crop plant. The results confirm that higher endopolyploidy occurs in plants with a smaller 2C DNA amount than in those with a larger one. The significance of endopolyplo- idization in development of sugar-beet plant organs is discussed. Keywords Somatic polyploidy Á Endoreduplication Á Flow cytometry Á Seed plant Á Ploidy level Introduction The presence of somatic cells with different ploidy levels in the same organ is called polysomaty; it is a common feature in over 90% of angiosperms (D’Amato 1984). Polysomaty is the consequence of endoreplication, a pro- cess during which nuclei undergo repeated rounds of DNA synthesis without mitosis, resulting in endopolyploid cells (Nagl 1976). This occurs during the cell differentiation, mainly in highly specialized cell types, such as vascular elements, storage cells of the endosperm or the embryo suspensor (List 1963; Nagl 1974; Kowles et al. 1992). Nagl (1976) made the assumption that during differentiation the most active cells need a certain DNA mass, which is essentially the same in all species of comparable com- plexity, and hence suggested that DNA endoreplication is an evolutionary strategy that substitutes for a lack of phylogenetic increase in nuclear DNA. The occurrence of a high systemic endopolyploidy in species with small ge- nomes such as Arabidopsis thaliana, Capsella bursa-pas- toris, Cucumis sativus and some succulents seems to confirm this hypothesis (Nagl 1976; De Rocher et al. 1990; Galbraith et al. 1991; Gilissen et al. 1993; Barow and Meister 2003). It was also suggested that the exclusion of endopolyploidy from the somatic cells of the floral struc- tures in polysomatic species avoids the potential produc- tion of polyploid gametophytes (Galbraith et al. 1991). Sugar beet (Beta vulgaris L.), with a DNA content of 1C = 0.8 pg = 782.4 Mbp (Bennett and Leitch 1995), can be considered a small genome species. However, in sugar- beet breeding, polyploid forms also occur, since most Communicated by J.S. Heslop-Harrison. E. Lukaszewska Á E. Sliwinska (&) Laboratory of Molecular Biology and Cytometry, Department of Genetics and Plant Breeding, University of Technology and Life Sciences, al. Kaliskiego 7, 85-789 Bydgoszcz, Poland e-mail: elwira@utp.edu.pl 123 Sex Plant Reprod (2007) 20:99–107 DOI 10.1007/s00497-007-0047-7