Pollen Size Research Articles

Pollen morphology of selected Camelineae (Brassicaceae)

ABSTRACTThe tribe Camelineae (Brassicaceae) contains eight genera: Arabidopsis, Camelina, Capsella, Catolobus, Chrysochamela, Neslia, Noccidium and Pseudoarabidopsis. Little is known about pollen morphology in these taxa, and this limits research on gene flow, aerobiology, reproductive biology, systematics and palaeobotany. In this study, pollen from 13 taxa representing all of the genera in the tribe Camelineae were examined using light and scanning electron microscopy. Measurements of pollen size in Camelina (mean 26.4 µm) and Arabidopsis (mean 30.4 µm) showed that these genera contain taxa with relatively large pollen that could be classified as medium-sized pollen. The largest pollen were from Camelina microcarpa (mean 37.6 µm) and C. sativa (mean 35.6 µm). Conversely, Pseudoarabidopsis had the smallest pollen (mean 18.4 µm) in the Camelineae. Capsella bursa-pastoris was distinct in the tribe in having tectum discontinuities. Catolobus and Neslia shared a similar pollen shape that tended to be subspheroidal and less prolate than others in the tribe. Noccidium had distinct microverrucate elements on its colpus membrane. Within Camelina, variations in pollen size and stratification were observed among the five species studied. The pollen morphology of Chrysochamela deviated from that of other members of the tribe, and it was distinct in having a homobrochate reticulum and the thickest exine, sexine and infratectum. These results support research on diverse topics including pollen dispersal and gene flow in Camelina, pollen development in Arabidopsis thaliana and phylogenetic studies in the Brassicaceae.

A cytogenetic study of R. constantinopolitanus and R. sericeus (Ranunculaceae) in Iran

With 600 species Ranunculus is the largest genus in Ranunculaceae, and has a broad global distribution. We studied the karyotypes of R. constantinopolitanus and R. sericeus species of Ranunculaceae and identified their symmetry level. New chromosome numbers of 2n = 21 (Nodeh woods population) and 2n ca. 63 (Javaherdeh population) are reported for R. constantinopolitanus. Two different populations of R. sericeus had two different chromosome results. We investigated morphological and karyological studies along with pollens micromorphology. Different populations of R. constantinopolitanus and R. sericeus, with different chromosome numbers showed morphological and micromorphological differences. Therefore, we considered the two populations of R. sericeus as cytotypes. There was a correlation between the studied morphological characters and pollen size with ploidy levels in the two R. constantinopolitanus populations.

Food niche of Exomalopsis (Exomalopsis) fulvofasciata Smith (Hymenoptera: Apidae) in Brazilian savannah: the importance of oil-producing plant species as pollen sources

ABSTRACTExomalopsis are ground-nesting species, and their food-niche breadth is little known due the difficulty in locating the nests and finding efficient bait plants to attract these bees. Some species of Exomalopsis were recorded as tomato, hot pepper and eggplant pollinators. Information about the food niche could be useful to increase Exomalopsis populations, providing consistent and comparable data for the enrichment of natural and crop areas with adequate plant sources. This study aimed to determine the food niche and the role of pollen size in the diet of E. fulvofasciata. We analysed pollen loads of 28 individuals of E. fulvofasciata collected from bait plants, in two natural areas of the Brazilian savannah. Only five pollen types belonging to the families Malpighiaceae, Solanaceae, Leguminosae, Myrtaceae and Lythraceae were important for this species. This result indicates that E. fulvofasciata is probably a polylectic species. However, we noticed that the Byrsonima used as bait plants contribute significantly for its larval provision, indicating that small pollen grains were more frequently collected.

Pollen morphology in two Urgineoid species of Drimia (Baker) Jessop

Pollen grains of eight accessions of Urginea indica (Roxb) Kunth. and two accessions of Urgineawightii (Wight) Lakshmin. were examined by Light microscopy and Scanning electron microscopy. Detailed pollen morphological characters are given for these accessions. Our investigation revealed several variations in pollen size, exine ornamentation among the accessions of U. indica (Roxb) Kunth. and U. wightii (Wight) Lakshmin. The study confirmed that the exine sculpting provides valuable characters for separating the species of Urginea. Reticulate ornamentation of the exine was observed in the accessions of U. indica complex and perforated exineornamentation in accessions of U. wightii complex. Minor variations with regard to measurements of dimensions in size, shape and ornamentation were also observed in accessions of U. indica and U. wightii . Pollen fertility analysis revealed highest percentage fertility in Sitampoondi accession of U. indica complex and Gulbargha accession of U. wightii complex but in most of the accessions seed setting is not observed in natural conditions. Pollen germination studies revealed highest germination rate in Brew Baker’s and Kwack medium supplemented with 25% sucrose concentration for Urginea pollen.

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.

An improved method for pollen release from anther: a case study with mangroves

The estimation of pollen production is widely used in pollination and reproductive ecology, aerobiology and pollen-vegetation relationship studies. Pollen release is the key step in estimating pollen production and therefore, the technique used to release pollen is critical. Three methods, the drying method (DM), mechanical method (MM) and chemical method (CM), are used to determine the amount of pollen released from anthers. Few studies have compared the results obtained from each method, making it difficult to determine which method is most appropriate in a given situation. In this study, we compared existing methods with a new method that increases the amount of pollen released from anthers. Eight species of mangrove trees from the Neilingding-Futian National Nature Reserve were selected for study. We combined the MM and CM to produce a new method (the ultrasonic method, UM). To determine the best ultrasonic treatment time using the UM, different durations were tested and the various responses were analysed. The relationships between pollen rupture and the ultrasonic treatment time, pollen size, exine thickness and aperture size were analysed. Finally, four methods for pollen release from anthers were compared. The results indicated that the UM could be an efficient method to release pollen from the anther. To avoid pollen rupture, ultrasonic treatment times in the UM should be less than 30 s. The pollen rupture rate was significantly correlated with the ultrasonic treatment time (r = 0.618, p < 0.001) and the aperture size (r = 0.248, p = 0.036). This comparative experiment indicated that the UM can generate a greater pollen yield than other methods while causing less pollen rupture than the MM. Therefore, the UM may be suitable for more plant species and more accurate for pollen production estimates than the existing three methods, particularly when estimating pollen production in all community plants.

Development and characterization of an interspecificGossypium hirsutumxGossypium armourianumhybrid

Interspecific hybrid between Gossypium hirsutum (AADD) cv. F 1861 and G. armourianum (DD) Acc. PAU 1 was generated and characterized along with parents at morphological and molecular levels. Female parent (F 1861) had erect growth habit, cream petals, palmate leaves, green stem, cream anthers, hairy stem and leaves; whereas male parent (PAU 1) had spreading growth habit, yellow petals, cordate leaves, reddish green stem, yellow anthers and glabrous plant body. The growth habit, petal colour, leaf shape and size of interspecific F1 hybrid were intermediate. Plant stem colour and hairiness, leaf pubescence and anther colour of G. armourianum Acc. PAU 1 were observed to be dominant as hybrid fully resembled Acc. PAU 1 for these characters. Petal spot was absent in F 1861 and present in PAU 1as well as hybrid. Variable expression of petal spot, anther colour and filament colour was observed in F1. The interspecific F1 hybrid was male-sterile. Significant differences were observed between the pollen size of parents as well as parents and their hybrid. Of the 33 SSR markers polymorphic between the parents, 8 markers unambiguously confirmed the hybrid status of interspecific hybrid. This hybrid may serve as a useful genetic resource for the transfer of cotton leaf curl disease resistance to American cotton.

Impact of terminal heat stress on pollen viability and yield attributes of rice (Oryza sativaL.)

Global warming is rising as a serious concern affecting agricultural production worldwide. Rice is a staple food crop and the threshold temperature for its pollination is 35 °C. A rise in temperature above this value can cause pollen sterility and may severely affect fertilization. Therefore, a study emphasizing the rise in temperature with respect to pollen viability was conducted with eleven rice genotypes during kharif seasons of 2010 and 2011 in indigenous field conditions. Increasing mean temperature by 12 °C at full flowering was found to severely affect the spikelet attributes of the crop. All genotypes showed spikelet sterility above 90% during both seasons. The study indicated that increased temperature may limit rice yield by affecting spikelet fertility and grain filling. The net reduction in grain yield was 30.4% and 27.6% in 2010 and 2011, respectively. A clear reduction in pollen size under high temperature was shown by scanning electron microscopy.

Pollen morphology of Poaceae (Poales) in the Azores, Portugal

The objective of this study was to expand knowledge on the Poaceae and morphologically describe pollen grains of species occurring in the Azores Archipelago, Portugal. Pollen grains from each species under study were subjected to standard acetolysis, mounting of at least three permanent slides of each species for observations and measurement of pollen grains under light and scanning electron microscope. With regard to pollen morphology, all pollen grains were arranged as monads, with a single pore-type aperture – monoporate, featuring annulus and operculum; and outline in polar view circular, sub-circular and ovalate. Most species featured pollen size small, except for Agrostis stolonifera with pollen size very small, Brachypodium sylvaticum with pollen size medium, Zea mays with pollen size large. Species endemic to the archipelago show ornamentation pattern ranging between areolate-microechinate, microechinate, microrugulate-microechinate and verrucate-microechinate, most of which feature exine surface areolate-microechinate. Among endemic species, Rostraria azorica stood out for its oblate-spheroidal shape, whereas most species showed prolate-spheroidal shape.

Pollen Structure and Diversity in Liliales

Premise of research. Family relationships in the monocot order Liliales have been revised recently, so that the order now consists of 10 families of geophytes and climbers, with unusually diverse pollen morphology. Corsiaceae are sometimes placed as sister to all other Liliales, probably allied with Campynemataceae. Relationships of the wild card family Petermanniaceae are unresolved. The remaining seven families are arranged in three clades.Methodology. We use SEM and TEM to describe the pollen of representatives of all 10 families of Liliales in order to investigate pollen character evolution.Pivotal results. Liliales pollen is unusually diverse in size (10–<80 μm), shape (mostly ellipsoidal, or circular to oval), apertures, and surface patterning. Apertures are predominantly monosulcate but frequently inaperturate; disulculate, trisulcate, monoporate (or ulcerate), and diporate forms also occur in different taxa. The sulcus or pore is often indistinct and may be covered by an operculum or areolae. Surface sculpturing ranges from perforate, reticulate, rugulate, striate, and crotonoid to types with raised elements, including scabrate, pilate, gemmate, and echinate. The exine is usually tectate-perforate or semitectate and columellate, though it can be reduced to granules or echini on top of a lamellated endexine.Conclusions. Our study indicates a strong potential correlation between pollen size and genome size. Some pollen characters appear to have evolved iteratively (e.g., operculate apertures). On the basis of character optimizations, the plesiomorphic pollen conditions for Liliales are probably small grain size, reticulate surface sculpturing, and a single elongated aperture.

High frequency of cytomixis observed at zygotene in tetraploid Lippia alba

Lippia alba (Verbenaceae) is an aromatic shrub recently described as a new tropical polyploid species with five distinct chromosome numbers (2n = 30, 38, 45, 60, and 90) with 2n = 30, 45, and 60 being the most frequent ones. Cytomixis is a cellular process known as the migration of genetic material mainly between meiocytes through cytoplasmic connections or cytomictic channels. This phenomenon has been reported in various plant families such as Leguminosae, Brassicaceae, Poaceae, Apocynaceae, Liliaceae, Rutaceae, and others. The transference of genetic material between pollen mother cells (PMCs), by cytomictic channels, induces the formation of unbalanced and unreduced (2n) gametes, and is considered a possible source of aneuploid and polyploid plants. Here, we describe for the first time, the occurrence of cytomixis in meiotic cells of L. alba (tetraploid cytotype) analyzing data obtained from meiotic behavior assays. In addition, the pollen size and viability were also evaluated. A high index of irregularities during meiosis was observed as well as unviable pollen with heterogeneous size. Approximately 80 % of zygotene cells showed genetic material exchange. Considering that L. alba shows different chromosome numbers, the contribution of cytomixis to cytotypes formation is also discussed.

Large pollen at high temperature: an adaptation to increased competition on the stigma?

Pollen availability is a major constraint of plant reproductive success. Because pollen size trades-off with the quantity of produced grains, the link between climate characteristics and the determination of pollen size is of fundamental importance. To minimize the rate of water loss due to desiccation, a plant should produce larger grains that also have a lower surface-to-volume ratio. We used a comparative analysis to examine the hypothesis predicting increase in pollen size as a response to desiccation intensity. To test the hypothesis, we correlated the data on pollen size with the climate characteristics, temperature and desiccation intensity of the flowering period, for 232 plant species of 11 taxonomic groups. The analysis showed a positive relationship between the pollen size and temperature, but not with the desiccation intensity. We discuss the potential mechanisms by which increased temperature is an indicator of high competition among pollen grains on the stigma, which in turn is expected to promote large pollen. Our work provides insight into the temperature dependence of pollen production in plants and reveals a link between environmental temperature and the intensity of limitation of plant reproductive success by pollen availability. The result is relevant in the context of global climate change. We also discuss why environmental temperature has to be controlled in studies dealing with pollen production, particularly in investigations of size-number trade-off.

Comparison of seven colchicine-induced tetraploid clones with their original diploid clones in purple coneflower (Echinacea purpurea L.)

Seven clones of colchicine-induced tetraploid purple coneflower (Echinacea purpurea L.) plants were grown on a farm for comparison with their corresponding original diploid plants. In the first year of cultivation, the plant height, number of capitula, and inflorescence (branched flower stalk) were significantly reduced in all of the tetraploid plants, while the length-to-width leaf ratio, pollen size, and root thickness were significantly increased. Although the tetraploid plants had larger seeds, most of the seeds of tetraploid plants were not fully filled and the naked seeds (i.e., seeds observed without the outer seed coat) were noticeably smaller than those of the diploid plants. In the second year of cultivation, the phenological stages were markedly delayed in the tetraploid plants; the number of capitula increased much more in tetraploid plants than in diploid plants. Among the seven tetraploid clones, two yielded significantly higher plant biomass and higher cichoric acid content per gram dry weight as well as per plant. The results of the present experiments indicate that some effects of tetraploidization of diploid E. purpurea are genotype-dependent, suggesting that the tetraploidization of more genotypes of the diploid is needed to breed better tetraploid varieties.

Pollen morphology and its taxonomic significance in the genus Bomarea Mirb. (Alstroemeriaceae) - I. Subgenera Baccata, Sphaerine, and Wichuraea

Pollen morphology of 24 of the 33 species of three Bomareasubgenera, Baccata, Sphaerine, andWichuraea, was examined by light microscopy (LM) and scanning electron microscopy (SEM), or SEM alone. The studied species ofBomarea were stenopalynous, characterized by large, monosulcate monads with reticulate exine sculpture in most species. Opercula-like structures were present on the sulcus in B.huanucoand B.involucrosa. Differences in pollen size, exine thickness, and exine sculpture were observed. The studied taxa were divided into four major groups based on exine ornamentation observed under SEM: microreticulate, reticulate, coarsely rugulate, or finely rugulate-perforate. Pollen characters alone did not appear to correlate clearly with the current subgeneric classification of Bomarea, but they may have some taxonomic utility below the subgeneric level. The most reliable infrageneric classification of Bomarea can be achieved through combined analyses of morphological, palynological, and molecular data from larger samples of specimens of all the species.

Micropollen Formation in F1 Hybrids and Backcrosses of Waterhemp (Amaranthus tuberculatus) X Smooth Pigweed (A. hybridus) as a Quick Method for Determination of Interspecific Hybridization Events

Various weedy amaranths have demonstrated the possibility of genetic exchange via interspecific hybridization. Normal meiotic events lead to the formation of normal tetrads and normal pollen while abnormal meiosis results in abnormal segregation of chromosomes in the tetrads resulting in macro and micropollen. Thus, pollen size can be used as an indirect measure of meiotic integrity. The purpose of this study was to examine the frequency of micropollen from putative F1, BC1, and BC2 progeny of waterhemp and smooth pigweed crosses to determine if infertility in the hybrids could be attributed to abnormal meiosis. Significant variation was observed with respect to the occurrence of micropollen. The F1 hybrids had the highest occurrence of micropollen, and highest percentage of abnormal tetrad formation. Problems in meiosis could be causing decreased fertility, but not complete sterility. However, backcrossing resulted in progeny with smaller percentages of micropollen, consistent with previous reports that fertility is restored in these progeny. This method allows for quick and cost effective method for determination of interspecific hybridization events.

Pollen morphology of some Brazilian Xyris Gronov. ex L. (Xyridaceae) species

Although the pollen morphology of Xyridaceae shows standard patterns that distinguish five genera, specific data of each genus are scarce or incompletely known. The pollen morphology of 17 Brazilian species of Xyris (Nematopus Section) based upon 47 specimens from Goias and Minas Gerais States, Brazil, is presented. Micrographs of pollen grain structures were obtained using light and scanning electron microscopy. Pollen grains are characterized as monads, medium to large sized, ellipsoidal in polar view, flattened/convex in equatorial view and monosulcates. The sulci are pontoperculate and covered with an insulae type membrane. The sexine presents either a microreticulum or rugulae with perforations, and is thicker than the nexine. Although Xyris is a stenopalynous genus, characterized by monosulcate pollen grains, two groups of species were recognized based upon pollen size as well as pollen wall ornamentation features. Therefore, pollen data are of taxonomic value and useful to clarify the delimitation of the studied species.

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.

The striking and unexpected cytogenetic diversity of genus Tanacetum L. (Asteraceae): a cytometric and fluorescent in situ hybridisation study of Iranian taxa.

BackgroundAlthough karyologically well studied, the genus Tanacetum (Asteraceae) is poorly known from the perspective of molecular cytogenetics. The prevalence of polyploidy, including odd ploidy warranted an extensive cytogenetic study. We studied several species native to Iran, one of the most important centres of diversity of the genus. We aimed to characterise Tanacetum genomes through fluorochrome banding, fluorescent in situ hybridisation (FISH) of rRNA genes and the assessment of genome size by flow cytometry. We appraise the effect of polyploidy and evaluate the existence of intraspecific variation based on the number and distribution of GC-rich bands and rDNA loci. Finally, we infer ancestral genome size and other cytogenetic traits considering phylogenetic relationships within the genus.ResultsWe report first genome size (2C) estimates ranging from 3.84 to 24.87 pg representing about 11 % of those recognised for the genus. We found striking cytogenetic diversity both in the number of GC-rich bands and rDNA loci. There is variation even at the population level and some species have undergone massive heterochromatic or rDNA amplification. Certain morphometric data, such as pollen size or inflorescence architecture, bear some relationship with genome size. Reconstruction of ancestral genome size, number of CMA+ bands and number of rDNA loci show that ups and downs have occurred during the evolution of these traits, although genome size has mostly increased and the number of CMA+ bands and rDNA loci have decreased in present-day taxa compared with ancestral values.ConclusionsTanacetum genomes are highly unstable in the number of GC-rich bands and rDNA loci, although some patterns can be established at the diploid and tetraploid levels. In particular, aneuploid taxa and some odd ploidy species show greater cytogenetic instability than the rest of the genus. We have also confirmed a linked rDNA arrangement for all the studied Tanacetum species. The labile scenario found in Tanacetum proves that some cytogenetic features previously regarded as relatively constant, or even diagnostic, can display high variability, which is better interpreted within a phylogenetic context.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0564-8) contains supplementary material, which is available to authorized users.

Potential Drift of Pollen of Cycas micronesica on the Island of Guam: A Comparative Study

We have investigated the potential movement on air currents of pollen from Guam’s native cycad, Cycas micronesica, proposed as ambophilic. We measured wind velocities and directions in different cycad habitats that vary in their exposure to trade winds, determined pollen settling velocities, and then modeled the potential horizontal pollen drift distance in each habitat. Similar measurements were performed on several entomophilous Zamia cycads and six zoophilous tropical trees used in horticulture or landscaping. All cycad species’ pollen exhibited relatively slow mean settling velocities (0.73–1.29 cm·s−1) with C. micronesica pollen in the middle of this range. Our models predicted that wind in more open habitats with wind directions east northeast (ENE) to northeast (NE) and velocities &gt;2 m·s−1 could transport C. micronesica pollen, either single grains or clumps, hundreds of meters downwind from the pollen source before falling 1 or 2 m. In forested habitats and at typical heights of cycad cones in the understory, the mean wind velocities ranged from &lt;0.03 m·s−1 to ≈1 m·s−1. In habitats with mean winds ≥0.2 m·s−1, models predicted pollen transport distances of tens of meters from the pollen source. In sheltered habitats with velocities near 0.03 m·s−1, the potential wind transport of pollen was limited to less than a few meters, suggesting that wind would be an ineffective vector in such areas. Pollen grains of all angiosperm species were larger except one, and the species with larger grains had settling velocities 3–26 times faster than that of cycad pollens. Even so, winds in most Guam environments could transport pollen of most angiosperm species over 50 m before falling 1 m. In summary, the results suggested that pollen size, clumping tendencies, and drift of most of these species do not preclude a role for wind in moving pollen in habitats exposed to trade winds, and that other physical and plant characteristics affect their pollination mode. For C. micronesica, these pollen and plant attributes do not preclude entomophily, and insects are likely required in the deep understory where cycads are present.

Differences in sculpture and size of pollen grains: new morphological evidence of diversification in Pelliciera rhizophorae, an ancient Neotropical mangrove species

The present study shows new evidence of morphological traits that supports the hypothesis of diversification between two genetic variants of Pelliciera rhizophorae (Tetrameristaceae), the most ancient species in the Neotropical mangrove ecosystem. Previous studies using molecular markers identified two variants of this species. Our new study, using pollen grain morphology, revealed differences in pollen sculpture between the two variants; that is, in Variant A the exine is characterised as perforate–verrucose, while in Variant B, it is punctuate. Pollen size in Variant A is larger than in Variant B, whereas the exine is thicker in Variant B than in Variant A. The differences in pollen morphology between the two variants represent new evidence suggesting that a diversification process might be occurring within P. rhizophorae, possibly due to adaptive processes in response to environmental conditions or pollination vectors.