MORPHOLOGICAL DIVERSITY OF POLLEN FROM SELECTED SPECIES OF THE GENUS TARAXACUM , ACCORDING TO THEIR PLOIDAL LEVEL

The study of the morphology of pollen concerned eight species of the genus Taraxacum . Seven types were chosen with a different number of chromosomes belonging to the section Palustria : Taraxacum paucilobum 2n = 3x = 24, T. subdolum 2n = 3x =24, T. subpolonicum 2n =3x = 24, T. vindobonense 2n = 4x = 32, T. trilobifolium 2n = 4x = 32, T. mendax 2n = 5x = 40, T. portentosum 2n =? and one type from the section Obliqua - T. platyglossum 2n =?. Pollen from all the examined species was observed by SEM microscopy. A distinct relation exists between the morphology of pollen and the way of reproduction. Pollen of triploidal species, being compulsory apomicts, is characterized by a great variability of the size and a high percentage of deformed pollen grains. Tetraploids, being optional apomicts, produce regular pollen with a relatively even size. The regular type of pollen in pentaploidal Taraxacum mendax and in species with an unknown number of chromosomes ( Taraxacum portentosum and T. platyglossum ) suggests that these taxa are optional apomicts.


INTRODUCTION
The genus Taraxacum Wigg.involves one of the biggest apomictic complexes of Magnoliophytina, at present there are nearly 3000 recognised species, divided into 51 sections (K i r s c h n e r and Š t ĕ p á n e k , 1997, 2004; U h l e m a n n et al. 2004).
Today there are about 400 species present in Poland, in 13 sections, 300 of which have been assigned to the section Ruderalia (G ł o w a c k i , 2004; M i r e k et al. 2002; T r á v n í č e k et al. 2007).This large and diverse group, in terms of morphological, caryological, biochemical and ecological criteria, is well known under a historical (nom.conservantum), but inappropria-te name of Taraxacum offi cinale.This name at present refers to the nomenclatoric boreal type of the middle section of Taraxacum which does not exist in Europe (K i r s c h n e r and Š t ĕ p á n e k , 1997).Blossoming dandelions of the section Ruderalia are considered to be important apicultural, nutritional and healing plants  2006), while there are numerous and well known species (including Ruderalia) that do not produce pollen or just a little amount of pollen.It must result in their variable effi ciency and honey yield, depending on the species.Differences in the size, shape and amount of produced pollen result from the ploidal number and related ways of reproduction (D o l l , 1973; S t e r k et al. 1982).Diploidal species of 2n = 16 use sexual reproduction and they produce signifi cant amounts of regular pollen with little size diversity.Triploidal plants with 2n = 24 reproduce in an apomictic way and obligatory apomixion is quite typical for them.Species that reproduce in this way produce pollen of diverse size, with numerous traits that suggest degeneration.K o ś c i ń s k a -P a j ą k (2006) observed two-and three-nuclear pollens in triploidal Taraxacum alatum, quite often they were narrowed and deformed.Species from higher ploidal number levels behave in a variable way.Tetraploids are quite often facultative apomictics that are capable of occasional sexual reproduction.Their pollen is regular and of low diversity scale (M a ł e c k a , 1965; 1967; 1973).In other poliploidal complexes (e.g.Achillea gender), a signifi cant corelation has been proven between the size of pollen and the ploidal level (D ą b r o w s k a , 1971).

MORPHOLOGICAL DIVERSITY OF POLLEN FROM SELECTED SPECIES OF THE GENUS TARAXACUM, ACCORDING TO THEIR PLOIDAL LEVEL
Jolanta Marciniuk1 , Anna Rudzińska-Langwald2 In this paper, an analysis of the morphology and size of pollen from selected dandelion species from the sections Palustria and Obliqua is presented.A close relation of these taxa to their natural and semi-natural location excludes the infl uence of industrial contamination.

MATERIALS AND METHODS
The research was conducted in 2006.Pollen of eight dandelion species was observed in the scanning microscope, seven of them belonging to the section Palustria (Taraxacum paucilobum, T. portentosum, T. vindobonense, T. trilobifolium, T. mendax, T. subpolonicum, T. subdolum) and Taraxacum platyglossum from the boreal, not present in Poland, section Obliqua.
Pollen for the analysis was taken from 14 herbarium specimens.For each of the species, a few hundreds pollen grains from at least three fl ower buds were observed.The sporoderm area was observed by scanning electronic microscopy.The open thecae were glued onto the microscopic table and sprayed with gold.SEM examination was carried out at the Nencki Institute of Experimental Biology in Warsaw.
Precise data, concerning their taxonomy appurtenance, origin and place of the material deposit, have been presented in Tab. 1.

RESULTS
Morphological diversity of pollen from different species seems to correlate with the chromosome number of the plants.Triploidal species -Taraxacum paucilobum, T. subpolonicum and T. subdolum (Figs 1 a, d, e) -have pollen of variable size and shape of grains, along with giant grains there are some dwarfi sh pollen grains.On the surface of the pollen numerous deformations were present, with a different shape and number of cavities (lacunae) as well as asymmetrical ribs.
The homogenic size and shape of pollen grains were typical for tetraploidal species -T.vindobonense and T. trilobifolium (Figs 1 c, g); a similar regular and even size of pollen grains was observed in pentaploidal Taraxacum mendax (Fig. 1 f).Pollen from Taraxacum portentosum (the species with an unknown chromosome number) possessed pollen of an even size, but most pollen grains were deformed -they were either asymmetrical or had a variable number and shape of lacunae and an irregular pattern of ribs (Fig. 1 b).Pollen from Taraxacum platyglossum had grains of similar size and regular shape.Small and diffi cult to notice lacunae were specifi c in this species (Fig. 1

DISCUSSION
The poliploidal number in dandelions resulted from spontaneous hybridisation between different species, typical for the natural world.Coming into existence in the end, poliploidal bastardized types as a rule demonstrate smaller or greater disorders of the process of meiosis and they use the apomictic way of reproduction (K i r s c h n e r and Š t ĕ p á n e k , 1996).Morphological diversity of pollen in Taraxacum, according to S t e r k et al. (1982), must be combined above all with the way of reproduction.The authors showed that sexual diploids produced very regular pollen of almost balanced size; species with optional or partly sexual apomicts produce regular pollen of little scale of diversity.
Compulsory apomicts produce irregular pollen with a very changeable size or do not produce it at all.The pollen of the examined types belongs to two catego-ries suggested by S t e r k et al. (1982).Triploidal species -Taraxacum paucilobum, T. subdolum and T. subpolonicum -produce irregular pollen of variable size that proves disordered meiotic transitions which result in the creation of grains with a changeable number of chromosomes, from haploidal to unreduced triploidal grains (M a r t o n f i o v a , 2006).The production of deformed and multinuclear grains is typical for such transitions and quite frequent (M a ł e c k a , 1964; K o ś c i ń s k a -P a j ą k , 2006).Relatively regular pollen of even size was reported in tetraploidal Taraxacum vindobonense and T. trilobifolium, pentaploidal T. mendax as well as in T. portentosum (an unknown number of chromosomes).Regular and even pollen proves normal processes of meiosis and they are typical of optional apomicts (S t e r k et al. 1982).The correct course of meiosis, producing regular pollen, and the occasional ability of sexual reproduction in tetraploidal Taraxacum vindobonense and pentaploidal Taraxacum skalinskanum have been indicated by M a ł e c k a (1973).Observed in SEM, pollen of Taraxacum platyglossum (the number of chromosomes unknown to the authors) had a big and even size and a regular shape of the grain.Such a structure of pollen proves the correct course of microsporogenesis, which is very interesting in the species that frequently does not produce pollen (D u d m a n and R i c h a r d s , 1997).It is possible that it results from caryological diversity of Taraxacum platyglossum.This issue needs more detailed research.

Zróżnicowanie morfologiczne pyłku wybranych gatunków rodzaju
(P o d b i e l k o w s k i , 1992; P o d b i e l k o w s k i and S u d n i k -W ó j c i k o w s k a , 2003).The research conducted so far, concerning pollen effi ciency and honey yield of dandelion fl owers, has been related to general species of Taraxacum offi cinale (W a r a k o m s k a , 1972; D e m i a n o w i c z , 1979; W a r a k o m s k a , 2002; W e r y s z k o -C h m i e l e w s k a and C h w i l ,