Occurrence Of 2n Pollen Research Articles

Colchicine induced manifestation of abnormal male meiosis and 2n pollen in Trachyspermum ammi (L.) Sprague (Apiaceae)

Unreduced gametes are the key source for the natural polyploidization in plants, but process of its formation is very low in nature. Meiotic mutants are second source for the formation of 2n pollen. In this cytological investigation, the meiotic aberrations and its impact on post-meiotic products were analysed in autotetraploid Trachyspermum ammi (L.) Sprague (4n=36). The seedlings of T. ammi (L.) Sprague were treated with 3 different concentrations of colchicine (0.2, 0.4 and 0.5%, w/v) for 3 different durations. Six polyploid plants were induced which was confirmed on the basis of cytological analysis. Colchicine, an anti-microtubular drug induced different meiotic and post-meiotic abnormalities such as chromosomal bridges, lagging chromosomes, scattering, precocious, fragments, dyads, triads, and polyads. The formation of several abnormal sporads clearly signifies the meiotic restitution. The tendency of univalents to scattered in the cytoplasm at metaphase was identified as a peculiar aberration asynapsis. Pollen variability and fusion of pollen walls was reported and pollen fertility was calculated. The morphological analysis of the pollen allowed us to confirm the occurrence of 2n pollen.

Genomic relationships between hexaploid Helianthus resinosus and diploid Helianthus annuus (Asteraceae)

Genus Helianthus comprises diploid and polyploid species. An autoallopolyploid origin has been proposed for hexaploid species but the genomic relationships remain unclear. Mitotic and meiotic studies in annual Helianthus annuus (2n = 2x = 34) and perennial Helianthus resinosus (2n = 6x = 102) as well as the F1 hybrids between both species were carried out. Chromosome counting confirmed the hybrid origin of the latter plants and their tetraploid condition. Bivalents in hybrids ranged from 12 to 28 (\( \bar{x} \) = 20.8). Univalents, trivalents and quadrivalents were also observed. Meiotic products comprised dyads, triads and normal tetrads and pollen grains were heterogeneous in size. These observations suggest the occurrence of 2n pollen in addition to the expected n. Genomic in situ hybridization (GISH) of total H. annuus DNA on H. resinosus chromosomes rendered weak but uniform signals; similar hybridization pattern was observed using three other annual species. Hybridization with H. annuus probe performed on root tip cells of F1H. annuus × H. resinosus hybrids revealed 17 chromosomes with a strong hybridization signal. GISH in hybrid meiocytes distinguished chromosomes from parental species and revealed autosyndetic pairing of H. resinosus chromosomes, allosyndetic pairing in bivalents, trivalents and quadrivalents, and the presence of univalents derived from parents, H. annuus and H. resinosus. Results obtained from classical and molecular cytogenetics do not support H. annuus as a direct ancestor of H. resinosus. The occurrence of allosyndetic pairing and the relatively high fertility of the F1 hybrids point to the possibility that useful genes could be transferred from H. resinosus to cultivate sunflower, although the effective rate of recombination has not been evaluated. GISH method proved effective to recognize parental chromosomes in H. annuus × H. resinosus progeny.

Distribution of Microtubular Cytoskeletons and Organelle Nucleoids During Microsporogenesis in a 2n Pollen Producer of Hybrid Populus

AbstractThe distribution of microtubular cytoskeletons and organelle nucleoids during microsporogenesis in Populus simonii Carr. x P. nigra L. ‘Tongliao’ was studied by indirect immunofluorescence and 4’,6-diamidino-2- phenylindole (DAPI) staining. Our purpose was to reveal the relationship between changes in microtubule and chromosome behavior and cytokinesis and to explain the mechanism of 2n pollen production. We observed stable frequencies of 2n pollen production, ranging from 1.56% to 2.29%, between 2006 and 2008. Moreover, conjoined pollen grains were also observed. Meiotic abnormalities, including univalents, lagging chromosomes and micronuclei, were observed during microsporogenesis. Triads and dyads were also detected in meiotic products. Parallel spindles in metaphase II were unable to fuse, owing to the existence of an organelle band. Regularly, in telophase II, primary phragmoplasts were organized between sister nuclei, and secondary phragmoplasts formed between non-sister nuclei. Cell plates were initiated by centrifugal expansion of phragmoplasts and cytoplasmic infurrowing started at the junctions between the microsporocyte wall and the expanded phragmoplasts. However, a secondary phragmoplast was absent in some microsporocytes. These observations suggest that the occurrence of 2n pollen may result from the partial failure of cytokinesis caused by the absence of secondary phragmoplasts in this hybrid.

Occurrence of viable unreduced pollen in a Begonia collection

Polyploidy is widespread in plants and has played a major role in the evolution and diversification of the plant kingdom. Unreduced (2n) gametes are an interesting tool for polyploidisation and the creation of genetic variation in plant breeding. Especially in ornamentals, polyploidisation can broaden attractive features within a species. A Begonia collection was screened on the occurrence of 2n pollen with the aid of four different techniques: pollen size measurement, flow cytometric analysis of nuclei isolated from germinated and non germinated pollen, investigation of the microsporogenesis and analysis of progeny. In ten of the 70 screened genotypes (B. dregei, B. pearcei, B. ‘Anna Christina’, B. ‘Bubbles’, B. ‘Florence Rita’, B. ‘Orococo’, B. ‘Rubaiyat’, B. ‘Spatflacier’, B. ‘Tamo’ and B276), large pollen were observed with a rather spherical than normal ellipsoidal shape. Flow cytometric data proved that these aberrantly shaped pollen were associated with 2n ploidy levels, although they were not always viable. Meiotic aberrations in these large pollen producers resulted mainly in dyads although also monads, triads and polyads were observed. Successful crosses were obtained with B. dregei, B. ‘Orococo’, and B276 as pollinators; DNA content had increased in all or a part of the progeny. The results show that the occurrence of 2n pollen is not a rare phenomenon in Begonia.

The occurrence of 2n-pollen and the origin of sexual polyploids in dihaploid roses (Rosa hybrida L.)

Haploidisation by in situ parthenogenesis of 4x R. hybrida resulted in the production of some dihaploid roses (2n=2x=14) able to produce viable pollen. A cytological study of microsporogenesis revealed that, although the first meiotic reductional division occurred normally, the second (equational) division was characterised by frequent abnormalities which concerned spindle formation and led to unreduced gametes of First Division Restitution (FDR) type. Analysis of the hybrid progeny of a parthenogenetically derived male fertile dihaploid plant revealed a selective advantage of the 2n-pollen, especially in the case of an hybridization with a tetraploid female parent. Moreover, crosses carried out among dihaploid partners always resulted in hybrids with ploidy levels≥ 3x.

Occurrence of 2n pollen and ps gene frequencies in cultivated groups and their related wild species in tuber-bearing Solanums

The gene frequency for parallel spindles (ps) was estimated from the frequency of plants producing 2n pollen in three cultivated groups: 2x Phureja (phu), 2x Stenotomum (stn), and 4x Andigena (adg), as well as in four related wild taxa: 2x Solanum brevicaule (brc), 2x S. sparsipilum (spl), 4x S. gourlayi (grl) and 4x S. gourlayi-S. infundibuliforme hybrids (grl-ifd). Plants with more than 1% large pollen were considered as 2n pollen producers. Observations of meiosis in a sample of 2n pollen-producing plants indicated that parallel spindles is the mechanism of 2n pollen formation. The number of plants with 2n pollen among the total examined was 228 plants (15.5%) of 1,473 in 2x spl, 31 (26.7%) of 116 in 2x brc, 92 (17.4%) of 528 in 2x stn, 665 (22.1%) of 3,008 in 2x phu, 731 (51.4%) of 1,421 in 4x adg, 591 (41.2%) of 1,436 in 4x grl, and 36 (64.3%) out of 56 in 4x grl-ifd. The ps gene frequencies assuming Hardy-Weinberg equilibrium were: 0.393 for 2x spl, 0.462 for 2x brc, 0.417 for 2x stn, 0.470 for 2x phu, 0.847 for 4x adg, 0.801 for 4x grl, and 0.895 for 4x grl-ifd. Twenty-five adg clones were randomly selected from a large population and were crossed with 2x clone W5295.7, which produces 2n pollen by parallel spindles (ps). The 4x progenies from 4x×2x crosses were used to determine the genotypes at the ps locus by screening 10-20 plants in each family for 2n pollen. Based on chromosome segregation at the ps locus, 9, 14, 1, and 1 clones were nulliplex, simplex, simplex or duplex, and duplex, respectively. The frequency of the ps gene in the adg population was estimated to be 0.825 and 0.815 for chromosome and chromatid segregation, respectively. The high frequencies of 2n pollen and the ps gene in cultivated 2x and 4x groups, and in wild taxa closely related to them, provide evidence for sexual polyploidization in the tuber-bearing Solanums.