Variation In Pollen Size Research Articles

Comparative Study on Pollen Viability of Camellia oleifera at Four Ploidy Levels

Oil tea (Camellia oleifera Abel.) is one of the most important woody edible oil tree species in China, with intraspecific polyploid. In order to study the variation in pollen size and vigor of C. oleifera at ploidy level, four ploidy covers a total of 32 types of Camellia pollens as the material for the experiment. The results showed that the pollen sizes of diploid, tetraploid, hexaploidy, and octaploid were positively correlated with the ploidy level. Pollen viability of C. oleifera was determined by fluorescein diacetate (FDA) dye solution staining and medium containing 10% sucrose, 0.01% boric acid, and 1% agar germination in vitro, which indicated that the pollen viability and germination rate of the hexaploid were relatively high among the four ploidy levels, at 79.69% and 71.78% respectively. The pollen vigor of diploid NR-3, tetraploid DP43, hexaploid CJ-12, and octoploid YNYC-1 was higher than that of other materials with the same ploidy level. Knowledge of different ploidy pollen sizes and pollen viability provides basic information for formulating pollen breeding plans and pollination methods of C. oleifera.

Comparative palynology and taxonomic implication of Jasminum L. (Oleaceae) species from Pakistan on the bases of scanning electron microscopy.

Jasminum L. is the largest genus containing ~200 species found wild mostly in the tropical regions of the world. The comparative palynological study of nine Pakistani Jasminum species with SEM showed zonocolpus, trilobate, and tricolpus pollen types with simple endocolpus apertures which are plesiomorphic and conserved in the Jasminum species. The equatorial pollen view was prolate, subprolate, and perprolate with elliptic, lobate, subcircular whereas polar view was subtriangular in all species. Few characters were specific to some species like heteropolarity in Jasminum grandiflorum and foveolate exine ornamentation with rounded heterobrochate in Jasminum angulare whereas reticulate and angular homobrochate character was common in other species. The UPGMA dendrogram based on qualitative characters did not support the phylogenetic classification of the genus Jasminum as these are highly conserved. The quantitative data showed more variation in some characters whereas few characters showed little or no variation. A greater variation in pollen size was observed among the variants of same species, for example, Jasminum humile showed highly variable polar length and equatorial diameter as compared to other species. Minimum variation was observed in colpus length which divided all species in to two groups. The large lumina were specific to Jasminum nitidum and broader muri was the prominent characteristic of Jasminum angulare. Some species like Jasminum sambac and Jasminum azoricum were unable to develop true pollen due to structural or functional disabilities. So, the quantitative characters of pollen are only suitable for palynological based grouping of Jasminum species but less suitable to infer their evolutionary relationship.

Pollen grain size associated with pollinator feeding strategy.

Angiosperm pollen grain diameter varies greatly from a few microns to over 100, but the selective forces driving the interspecific variation in pollen size remain unclear. Although both pre- and post-pollination hypotheses have been proposed, empirical evidence remains scarce. Here we propose that visits by pollen-foraging pollinators have selected against large pollen grains. An association between pollinator behaviour and pollen grain size was confirmed by field studies of 80 flowering species in natural communities, showing that pollinators positively collected pollen in those species with relatively smaller pollen grains but rarely did so in species with larger ones. Allowing for the confounding effects of pollinator type, flower size or style length and pollen grain number, we found a significant effect of pollen-foraging behaviour on variation in pollen grain size, particularly in bee-pollinated plants. While these results suggest that many plant species whose pollen is collected or consumed by pollinators produce small pollen grains, it remains unclear whether pollen grain size is directly affected by pollinator foraging habit or indirectly mediated by pollen number trade-offs.

Phylogeographic insights on the evolutionary breakdown of heterostyly.

The breakdown of heterostyly to homostyly is a classic system for the investigation of evolutionary transitions from outcrossing to selfing. Loss of sexual polymorphism is characterized by changes to population morph structure and floral morphology. Here, we used molecular phylogeography to investigate the geographical context for the breakdown process in Primula chungensis, a species with distylous and homostylous populations. We genotyped plants from 20 populations throughout the entire range in south-west China using the chloroplast intergenic spacer (trnL-trnF), nuclear internal transcribed spacer (ITS) and 10 nuclear microsatellite loci, and determined the genetic relationships among populations and the variation in floral traits associated with homostyle evolution. The marker data identified two multi-population lineages (Tibet and Sichuan) and one single-population lineage (Yunnan), a pattern consistent with at least two independent origins of homostyly. Evidence from flower and pollen size variation is consistent with the hypothesis that transitions to selfing have arisen by the same genetic mechanism involving recombination and/or mutation at the distyly linkage group. Nevertheless, flowers of homostylous lineages have followed divergent evolutionary trajectories following their origin, resulting in populations with both approach and reverse herkogamy. Our study illustrates a rare example of the near-complete replacement of sexual polymorphism by floral monomorphism in a heterostylous species.

Estimating paternal efficiency in an agamic polyploid complex: pollen stainability and variation in pollen size related to reproduction mode, ploidy level and hybridogenous origin in Pilosella (Asteraceae)

Pollen quality was evaluated in Pilosella plants sourced from the field and representing various cytotypes (diploid to octoploid), reproduction modes (sexuality, facultative apomixis and seed sterility or semisterility) and status of origin (basic species, hybridogenous intermediate species and recent hybrids). Two methods of non-vital pollen staining were compared, providing a similar pattern of variation in pollen stainability and pollen size. A complex influence of ploidy level, reproduction mode and plant origin on pollen quality was found. Sexual biotypes had high and equable pollen stainability whereas apomictic and (semi)sterile plants were more variable in this trait. Nevertheless, the sexual, apomictic and (semi)sterile plants did not significantly differ in pollen stainability, while the impacts of both ploidy level and plant origin were significant. Apomictic triploids had low pollen stainability and heterogeneously sized pollen, most likely resulting from disturbed meiosis. The other biotypes, including higher odd-ploid cytotypes, displayed various patterns of pollen quality partially depending on the hybridogenous origin. Whereas high pollen quality was detected in most of the apomictic hexaploids and heptaploids, including recent hybrids, serious pollen dysfunction was found in most octoploids. Seed (semi)sterility was not strongly associated with reduced pollen quality. Either blocked or unstable pollen production was occasionally recorded, predominantly among recent hybrids. Despite autonomous apomixis independent of pollen, most apomictic biotypes displayed fairly high pollen stainability and pollen size homogeneity, implying sufficient production of viable reduced pollen. Most representatives of this agamic polyploid complex, including facultative apomicts, might efficiently mate as both male and female parents in natural populations.

Pollen competition in style: Effects of pollen size on siring success in the hermaphroditic common morning glory, Ipomoea purpurea.

Pollen size varies greatly among flowering plant species and has been shown to influence the delivery of sperm cells to the eggs. Relatively little is known, however, about the functional significance of within-species genetic variation in pollen size. This study tests whether pollen size influences the relative siring success of a pollen donor during in vivo pollen competition experiments. We used two groups of Ipomoea purpurea plants genetically divergent in their pollen sizes and applied equal number of pollen grains from one large-pollen and one small-pollen donor onto the same stigma. Using microsatellite genetic markers, we identified the pollen parent of each of the resulting progeny to determine the relative siring success of the competing donors. Competitions between donors of equal-sized pollen served as a control. Differences in pollen size significantly affected the relative siring success of a pollen donor; larger-grained individuals outcompeted smaller-grained competitors but not equal-sized competitors. Relative siring success, however, sometimes varied across different pollen recipients. Pollen size can influence the relative siring success of different individuals competing on the same stigma during postpollination processes. However, other factors, such as pollen-pistil interaction and environmental conditions, are likely to influence these competitions as well.

Pollen variation as a response to hybridisation in Populus L. section Aigeiros Duby

Interspecific hybrids often produce extensive gametic variation due to poor chromosome pairing and unbalanced chromosome segregation. To elucidate the influence of interspecific hybridisation on pollen variation in Populus L., we compared pollen size among three P. deltoides Marsh. clones, two P. nigra L. clones, and three P. deltoides × P. nigra hybrids and investigated the cytological mechanism of pollen variation by observing meiotic chromosome behaviour and microtubules. The frequency of shrunken and unstainable pollen grains was higher in the hybrids (15.54–57.28 %) than in the non-hybrid clones (0.98–4.82 %). The distribution of stained pollen size ranged more broadly in the hybrids than in the non-hybrids, suggesting that hybridisation increases pollen size variation. Precocious chromosome migration and lagging chromosomes were common in the hybrids, indicating poor chromosome pairing. Some micronuclei formed minispindles in metaphase II and emanated secondary nuclear-based radial microtubule systems in telophase II, undergoing cytokinesis to develop into microcytes in the meiotic products. Eliminated micronuclei might result in the formation of aneuploid pollen. The frequency of sporads with microcytes was higher in the hybrids (3.19–11.08 %) than in the non-hybrids (0–0.94 %). Disoriented spindles, including fused and tripolar spindles, led to the formation of dyads and triads, contributing to unreduced pollen production. These results provide new insights into the gametic variation of Populus interspecific hybrids and reveal several 2n pollen producers, which will be valuable in polyploid breeding of the section Aigeiros Duby.

Cytogenetic study and meiotic behaviour on 13 populations ofFibigia(Brassicaceae) in Iran

The present study reports the chromosome numbers and meiotic behaviour of 13 populations of four species of the genus Fibigia, including the first cytogenetic report of Fibigia clypeata from Iran. Most populations showed the chromosome numbers 2n = 2x = 16. However, the chromosome numbers of four populations of Fibigia suffruticosa were 2n = 2x = 14. It seems that the species with x = 7 is derived through aneuploidy loss. In addition, intraspecific and interspecific variations in the chromosome number and aneuploidy within Fibigia are discussed. The meiotic abnormalities observed in different Fibigia species included various degrees of fragmented chromosomes, sticky chromosomes, laggards, asynchronous nucleus, formation of multipolar cells, bridges and cytomixis. Various meiotic abnormalities caused pollen sterility and pollen-size variation. We are of the opinion that a direct relationship exists between the occurrence of chromosome number change and environmental stress. So, it seems that aneuploids pre...

Aberrant Classopollis pollen reveals evidence for unreduced (2n) pollen in the conifer family Cheirolepidiaceae during the Triassic-Jurassic transition.

Polyploidy (or whole-genome doubling) is a key mechanism for plant speciation leading to new evolutionary lineages. Several lines of evidence show that most species among flowering plants had polyploidy ancestry, but it is virtually unknown for conifers. Here, we study variability in pollen tetrad morphology and the size of the conifer pollen type Classopollis extracted from sediments of the Triassic-Jurassic transition, 200 Ma. Classopollis producing Cheirolepidiaceae were one of the most dominant and diverse groups of conifers during the Mesozoic. We show that aberrant pollen Classopollis tetrads, triads and dyads, and the large variation in pollen size indicates the presence of unreduced (2n) pollen, which is one of the main mechanisms in modern polyploid formation. Polyploid speciation may explain the high variability of growth forms and adaptation of these conifers to different environments and their resistance to extreme growth conditions. We suggest that polyploidy may have also reduced the extinction risk of these conifers during the End-Triassic biotic crisis.

Meiotic Abnormalities in Intergeneric Hybrids between Saccharum spontaneumand Erianthus arundinaceus (Gramineae)

Cytological studies were made in hybrids between S. spontaneum L clone Iritty-2 (2n=64) and Erianthus arundinaceus (Retz.) Jesweit clone IK 76-99 (2n=60). The chromosome number of 19 hybrids ranged from 2n=78 to 86. Predominantly bivalent formation was observed at diakinesis and metaphase I stages in pollen mother cells of all the hybrids. At later meiotic stages abnormalities such as lagging chromosomes, multipolar spindles, abnormal planes of cytokinesis and micronuclei were present. In one hybrid CYM 04-391 with chromosome number 2n=80, the pollen mother cells had cytomixis and syncyte formation in the prophase stage. Certain syncytes had very high number of chromosomes in the form of bivalents at diakinesis and metaphase I, with nearly 80 to more than 600 bivalents. Fertile pollen was observed in few anthers of CYM 04-391 and the pollen size variation was high in it compared to that in the other similar hybrids.

Variation in Nuclear DNA Content at the Species Level in Armeria Maritima

Intraspecific variation in nuclear DNA content in 19 populations of Armeria maritima was investigated. Significant differences in DNA amount among ecogeographic groups and among populations were observed. These differences are related to geographic origin, with Californian populations having 7 % more DNA than their European counterparts. Within Europe, the four ecogeographic groups tested are not distinct, whatever their geographic origin (maritime versus continental) and their ecological characteristics (heavy-metal polluted versus non-toxic soils). However, significant differences in DNA amount appeared among population clusters identified from biochemical classification of European populations based on flavonoid compounds and isozyme markers. Variation in genome size among populations was found to be significantly correlated to variation in pollen size. Weak interpopulational variation has been detected for the nucleotidic base ratio, but was not correlated to variation in DNA amount.

Pollen-pistil relationships and pollen size-number trade-off in species of the tribe Lycieae (Solanaceae).

Pollen volume may be involved in different associations with other floral traits. Particularly, the literature indicates that pollen volume can be implicated in a functional relationship with pistil length, and that it may be affected by a trade-off with pollen number because of the subdivision of limited resources. To assess these associations, pollen volume was subjected to correlation analyses with pollen number and pistil length in 20 Argentinean and Chilean taxa of the monophyletic tribe Lycieae. Depending on the mechanisms operating on pollen size and number, the variability of these traits may be different. Therefore, their coefficients of variation were compared. Pistil length and pollen volume showed a strong positive correlation. In contrast, pollen grain size and number were significantly correlated at neither inter- nor intraspecific levels. Results suggest that pollen size and pistil length may co-evolve. The central role of this interaction is discussed. The lack of a correlated variation in pollen size and number may be related to the similar constraints experienced by the species and/or because constraints are operating at the plant level and not at the species level. Lower variance in pollen size compared with pollen number denotes that pollen size may be the main trait subjected to natural selection.

A method to estimate pollen viability from pollen size variation

The mean diameter of viable pollen grains is approximately 13 μm greater than the mean diameter of inviable grains in Mimulus guttatus. We show that this difference is large enough to be detected by particle counters and that these machines can be used to obtain a rapid estimate of pollen viability. While requiring a separate calibration, a size-based statistic is also strongly correlated with pollen viability in Collinsia verna. These results suggest that statistics derived from the size distribution of pollen grains may provide an alternative to more labor-intensive methods for estimating pollen viability, particularly in cases where inviability results from inbreeding depression or hybrid failure.

Direct and indirect responses to selection on pollen size in Brassica rapa L.

Abstract Pollen size varies little within angiosperm species, but differs extensively between species, suggesting the action of strong selection. Nevertheless, the potential for genetic responses of pollen size to selection, as determined by additive genetic variance and genetic correlations with other floral traits, has received little attention. To assess this potential, we subjected Brassica rapa to artificial selection for large and small pollen during three generations. This selection caused significant divergence in pollen diameter, with additive genetic effects accounting for over 30% of the observed phenotypic variation in pollen size. Such heritable genetic variation suggests that natural selection could effect evolutionary change in this trait. Selection on pollen size also elicited correlated responses in pollen number (–), flower size (+), style length (+), and ovule number (+), suggesting that pollen size cannot evolve independently. The correlated responses of pollen number, flower size and ovule number probably reflect the genetically determined and physically constrained pattern of resource allocation in B. rapa. In contrast, the positive correlation between pollen size and style length may represent a widespread gametic-phase disequilibrium in angiosperms that arises from nonrandom fertilization success of large pollen in pistils with long styles.

Pollen morphology in Cytisus (Papilionoideae, Leguminosae) from Morocco and the Iberian Peninsula

Although it is generally accepted that the tribe Genisteae has rather homogeneous pollen, we have found considerable variation in pollen size and morphology in Cytisus and related genera (Argyrocytisus and Chamaecytisus), which match taxonomic groups defined on morphological grounds. The results of Principal Component Analysis of pollen characteristics show the following: Cytisus Sect. Alburnoides is well-delimited, with the smallest pollen grains and the simplest pattern in the tectum, fossulate-perforate to perforate; No separation of C. villosus (Sect. Cytisus) from Sect. Alburnoides is observed; Cytisus Sect. Spartopsis, with the largest pollen grains and reticulate to reticulate-fossulate ornamentation, forms an isolated group; C. fontanesii (Sect. Heterocytisus) stands apart from other Cytisus species by its homogeneous ornamentation and the perforate instead of psilate-punctate margo. Thus, the pollen data supports its transfer to the separated genus Chronanthos; Pollen ornamentation and morphology also support the separation of Argyrocytisus battandieri and Chamaecytisus mollis from Cytisus.

Pollen-size comparisons among animal-pollinated angiosperms with different pollination characteristics

Pollen volume varies among angiosperm species over five orders of magnitude, presumably because the functional advantages of pollen size depend on each species» particular pollination and fertilization conditions. This paper reports two studies that assess whether animal-pollinated species with different pollination systems differ correspondingly in pollen size, as would be expected if pollen size affected pollen transport. Analysis of ninePedicularisspecies detected significant interspecific variation in pollen size; however, the overall mean pollen volume of species pollinated primarily by nectar-collecting bees did not differ significantly from that of species pollinated by pollen-collecting bees. Similarly, comparison of bee- and bird-pollinated congeners in 16 genera (nine families) from Australia and North America found considerable variation in pollen diameter within and between genera, but this variation was not associated consistently with differences in primary pollinator type (bee>bird for three genera, bee≈bird for five genera, bee<bird for eight genera). These results imply that pollen-transport conditions likely play a minor role in the evolution of pollen size, at least for bee- and bird-pollinated species. Hence, interspecific pollen-size variation more probably reflects differences in conditions for pollen germination, pollen-tube growth and ovule fertilization.

Pollen-size comparisons among animal-pollinated angiosperms with different pollination characteristics

Pollen volume varies among angiosperm species over five orders of magnitude, presumably because the functional advantages of pollen size depend on each species» particular pollination and fertilization conditions. This paper reports two studies that assess whether animal-pollinated species with different pollination systems differ correspondingly in pollen size, as would be expected if pollen size affected pollen transport. Analysis of ninePedicularisspecies detected significant interspecific variation in pollen size; however, the overall mean pollen volume of species pollinated primarily by nectar-collecting bees did not differ significantly from that of species pollinated by pollen-collecting bees. Similarly, comparison of bee- and bird-pollinated congeners in 16 genera (nine families) from Australia and North America found considerable variation in pollen diameter within and between genera, but this variation was not associated consistently with differences in primary pollinator type (bee>bird for three genera, bee≈bird for five genera, bee<bird for eight genera). These results imply that pollen-transport conditions likely play a minor role in the evolution of pollen size, at least for bee- and bird-pollinated species. Hence, interspecific pollen-size variation more probably reflects differences in conditions for pollen germination, pollen-tube growth and ovule fertilization.

Ephedroid fossil pollen from the Lower Cretaceous (Upper Albian) of Hokkaido, Japan

This paper presents eight ephedroid palynomorphs from the Lower Cretaceous (Upper Albian) of Hokkaido, Japan. The ephedroid palynomorphs are ellipsoid and polyplicate pollen grains that show a wide range of variation in pollen size, shape, and plication. These ephedroid palynomorphs suggest a wide range of diversity in Gnetales at mid- or high-paleolatitude in the eastern side of Lauresia during the Upper Albian.

Temporal and spatial variation in heritability and genetic correlations among floral traits in Raphanus sativus, wild radish

We measured heritability and genetic correlations of three floral traits (corolla width, pollen production per flower and pollen size) in two generations of wild radish (Raphanus sativus) grown in three growth environments (two field sites and the greenhouse). Corolla width and pollen production showed significant heritabilities in both generations and under all growth environments, while pollen size variation appears to be under little genetic control. The estimates of heritability did not vary significantly among generations or among the growth environments. Genotype-environment interactions were not apparent for any trait. Apparently, similar selection pressures will result in similar phenotypic changes across generations and across sites. Only corolla width and pollen production were significantly genetically correlated; families with large corollas also had large pollen production. Therefore the direction and magnitude of evolutionary change of these two traits are dependent on the relative selection pressures on each.

Karyotypes and meiosis of cultivated and wild ulluco

SUMMARYThe karyotype and meiosis of wild and cultivated ulluco were analysed. All wild ulluco clones studied were triploids, 2n = 36, and all cultivated ones diploids, 2n = 24. A tetraploid cell line, 2n = 48 was found in a cultivated clone. Cultivated and wild ulluco have a similar set of chromosomes, with two pair of long, two pair of short and eight pair of intermediate chromosomes, and with two pair of satellite chromosomes. This indicates that the basic chromosome number of ulluco may be x = 6. Male and probably also female meiosis of diploid cultivated ulluco is regular and pollen stainability high. Reasons for the poor seed set of cultivated ulluco are to be looked for in other processes than meiosis. Meiosis of triploid wild ulluco is irregular, leading predominantly to aneuploid gametes, pollen stainability was low, and there was more variation in pollen size than in cultivated ulluco, most probably because of aneuploidy.