Biologia 65/6: 954—957, 2010 Section Botany DOI: 10.2478/s11756-010-0107-6 Differentiation of the pollen size in five representatives of Taraxacum sect. Palustria Jolanta Marciniuk1, Aleksandra Grabowska-Joachimiak2 & Pawe
l Marciniuk1 1 Department of Botany, University of Podlasie, Prusa 12, 08–110 Siedlce, Poland; e-mail: jolam@ap.siedlce.pl Cytogenetics Group in the Department of Plant Breeding and Seed Science, University of Agriculture in Cracow, L
obzowska 24, 31–140 Cracow, Poland; e-mail: rrjoachi@cyf-kr.edu.pl. 2 Abstract: Measurements of the pollen size in 5 species of Taraxacum sect. Palustria at three levels of ploidy: 2n = 3x = 24 (T. paucilobum), 2n = 4x = 32 (T. vindobonense, T. trilobifolium), 2n = 5x = 40 (T. mendax) and one taxon of unknown number of chromosomes 2n = ? (T. portentosum) are presented in this paper. Obtained results indicate a lack of distinct positive correlation between the pollen size and ploidy in the studied group of plants. Distinct relationship was, however, found between ploidy and the range of pollen size and shape variability. Most variable were the pollen grains of triploid T. paucilobum and the least – those in pentaploid T. mendax. Ranges of pollen variability in tetraploid T. trilobifolium and T. vindobonense and in T. portentosum of unknown number of chromosomes showed intermediate values. Key words: Taraxacum sect. Palustria; pollen size; polyploid series Taraxacum sect. Palustria involves ca. 130 species growing mainly in Europe. Asiatic range of the section Palustria is limited to Anatolia, northern Iraq and northern Iran (Kirschner & Štěpánek 1998). Species listed to this section form well developed polyploid series from sexually reproducing diploid Taraxacum tenuifolium to hexaploid T. ranunculus (Kirschner & Štěpánek 1998). In Poland the section Palustria is represented by 21 apomictic species (Mirek et al. 2002; G
lowacki 2004), mainly triploids, less frequently by tetraploids and by one pentaploid – Taraxacum mendax. Morphologic parameters of the pollen, especially its size and regularity, enable to preliminary distinguish diploid species of sexual reproduction from polyploid apomictics in the genus Taraxacum (Ma
lecka 1964; Doll 1973, 1974; Sterk et al. 1982; Zhai & An 1996; Meirmans et al. 2006). In other polyploid complexes (e.g. in the genus Achillea) there was distinct positive correlation between pollen size and ploidy of particular plants (D˛abrowska 1971). So, the question is: do similar correlations (between pollen size and ploidy) exist in polyploid series of the genus Taraxacum section Palustria? Material and methods This paper presents analyses of morphology and pollen grain size of five dandelion species from the section Palustria at three levels of ploidy. Close attachment of analysed taxa to natural and seminatural habitats prevents pollen deformation caused by industrial pollution. Pollen for analyses was collected from plants grown in private collection of J. Marciniuk. Fifty individuals (10 from c 2010 Institute of Botany, Slovak Academy of Sciences
each species) were selected. Sampling made in culture conditions minimised the effect of variable environmental conditions on pollen size. At least 100 grains were measured for every specimen (minimum 1000 measurements for each species) collected from closed buds just before flowering, which had been macerated before in 10% KOH. Measurements were made with the ocular micrometer at magnification of 1.5×10×40 (micrometric constant – 1.1). Pollen grain size was determined by measurements of maximum external and internal diameters in polar position. Results Taraxacum paucilobum Hudziok – one of the most common representatives of the section Palustria in Central Europe known from many sites in Slovakia, Czech Republic, Poland, eastern Germany and northern Austria. It is a rare species in Croatia, Bosnia and Herzegovina, Romania and Hungary (Kirschner & Štěpánek 1998). Taraxacum paucilobum is a triploid species 2n = 2x = 24 (Kirschner & Štěpánek 1998). Pollen of this species is relatively small – its external diameter was 35.77 µm on average; internal diameter was 24.32 µm. Pollen shows a large variability of grain size and is very irregular. Moreover, it had many deformed grains – 38% out of 1080 grains measured by authors (Table. 1). Taraxacum portentosum Kirschner & Štěpánek – very rare species in Europe; it occurs mainly in eastern Poland (Marciniuk & Marciniuk 2006) and is known from single sites in Czech Republic and Slovakia (Kirschner & Štěpánek 1998). The number of chromo- Pollen size in five representatives of Taraxacum sect. Palustria 955 Table 1. The number of chromosomes and pollen grain size in selected species of Taraxacum. External diameter in µm Species Taraxacum Taraxacum Taraxacum Taraxacum Taraxacum Internal diameter in µm 2n paucilobum portentosum vindobonense trilobifolium mendax 24 ? 32 32 40 minimum maximum mean minimum maximum mean % of deformed 20.9 27.5 19.8 33 28.6 59.4 48.4 50.6 59.4 46.2 35.77 41.34 37.60 39.90 37.66 8.8 19.8 22 19.8 18.7 50.6 39.6 34.1 37.4 33.0 24.32 29.65 27.11 27.35 26.44 32 10 14 12 8 somes is not known in this species. Its pollen was relatively large (mean external diameter was 41.34 µm and internal – 29.65), regular (10% deformed pollens) of low size variability (Table 1). 70 60 50 40 Taraxacum vindobonense Soest – relatively common species in Czech Republic, Slovakia, Hungary, northern Austria and southern Poland. It is rare in Germany and Ukraine (Kirschner & Štěpánek 1998; Schmid 2002; Uhlemann 2003; Marciniuk & Marciniuk 2006). Taraxacum vindobonense is a tetraploid 2n = 4x = 32 (Ma
lecka 1972; Kirschner & Štěpánek 1998). Pollen analysed by authors was rather regular (14% deformed pollens) but variable in external diameter (19.8–50.6 µm). Mean external and internal diameters were 37.60 µm and 27.11 µm, respectively (Table 1). Taraxacum trilobifolium Hudziok – is a tetraploid 2n = 4x = 32 species present in Central Europe: in Poland Czech Republic and Germany and seldom in Switzerland and Austria (Kirschner & Štěpánek 1998; Schmid 2002; Uhlemann 2003). Pollen of Taraxacum trilobifolium was relatively large (mean external diameter 39.90 µm, internal diameter 27.35 µm), quite regular (12% of deformed grains) and even (33–59.4 µm) (Table 1). Taraxacum mendax Kirschner & Štěpánek – most sites of this species are situated in the Western Carpathians (Poland, Slovakia, Czech Republic); it is also known in Hungary, Austria and Slovenia (Kirschner & Štěpánek 1998). Taraxacum mendax is a pentaploid species 2n = 5x = 40 (Kirschner & Štěpánek 1998). Pollen of studied individuals was regular (only 8% deformed grains), rather even and not big. Its mean external diameter was 37.66 µm and internal diameter – 26.44 µm (Table 1). Comparison of morphologic parameters (Figs 1, 2, 3a, b) demonstrated that the smallest and at the same time most variable pollen (in terms of both internal and external diameter) was produced by triploid Taraxacum paucilobum. Pollen of tetraploid T. trilobifolium and T. vindobonense was clearly larger and less variable, which was particularly visible in measurements of external diameter in T. vindobonense. Pentaploid T. mendax produced regular pollen of the narrow range of size variability close to that of triploid T. paucilobum. T. portentosum had the largest pollen grains. This species of unknown number of chromosomes was similar in the range of grain size variability to tetraploid T. trilobi- 30 20 10 0 5-9,9 10-15 15,120 20,125 25,130 30,135 35,140 T. portentosum T. trilob ifolium T. mendax T. paucilob um 40,145 45,150 50,155 55,160 T.vindob onense Fig. 1. Percentage share of pollen grains in particular size classes in µm – internal diameter. folium and T. vindobonense and it is possible that it is also a tetraploid. Discussion Performed measurements of pollen grain sizes in five species of Taraxacum from the section Palustria did not show clear relationship between pollen size and ploidy. The pollen of pentaploid Taraxacum mendax was smaller than that of tetraploid Taraxacum trilobifolium, comparable with the pollen of also tetraploid Taraxcum vindobonense and only slightly larger than the pollen of triploid Taraxacum paucilobum. Doll (1973) also failed to show such relationship in the section Erythrosperma. In the opinion of Sterk et al. (1982), morphological pollen differentiation in Taraxacum should be associated with the mode of reproduction. These authors found that diploid species of sexual reproduction produce very regular pollen of a minimum size variation. Facultative apomictics, irrespective of ploidy, produce pollen of low size variability, rather regular with a small number of deformed grains. Pollen of species reproducing by obligatory apomixis is characterised by large variability in both size (frequent dwarf and gigantic grains) and shape. Studied species belong to the two categories proposed by Sterk et al. (1982). Triploid Taraxacum paucilobum produced irregular pollen of large size variability which indicates obligatory apomixis. However, according to Martonfiova (2006), so diversified pollen is produced due to J. Marciniuk et al. 956 80 70 60 50 40 30 20 10 0 5-9,9 10-15 15,1-20 20,1-25 25,1-30 30,1-35 35,1-40 40,1-45 45,1-50 50,1-55 55,1-60 T. portentosum T. trilobifolium T. mendax T. paucilobum T.vindobonense Fig. 2. Percentage share of pollen grains in particular size classes in µm – external diameter. facultative apomictics (Sterk et al. 1982). Proper course of meiosis, production of regular pollen and sporadic capability of sexual reproduction in tetraploid Taraxacum vindobonense and pentaploid Taraxacum skalinskanum was underlined by Ma
lecka (1973). It is not, however, a rule that species at higher level of ploidy produce more regular and even pollen than triploids. There is a group of tetraploids in the very section of Palustria that show full male sterility demonstrating itself by a total lack of pollen production (Kirschner & Štěpánek 1998). References Fig. 3. Range of size variability of pollen grains in five species of Taraxacum sect. Palustria in µm; a – internal diameter; b – external diameter. strong disturbances in meiotic divisions which result in the development of grains of variable chromosome numbers from haploid to non-reduced triploid grains. Large part of these grains is viable and capable of generative reproduction. Regular and even pollen grains produced by other species (tetraploid T. vindobonense and T. trilobifolium; pentaploid T. mendax and T. portentosum of unknown number of chromosomes) indicate relatively proper course of meiosis and are characteristic for D˛abrowska J. 1971. Wielkość komórek szparkowych i py
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