Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Pollen

  • allergenic pollen
  • bee pollen
  • birch pollen
  • conspecific pollen
  • cypress pollen
  • fossil pollen
  • grass pollen
  • modern pollen
  • outcross pollen
  • tree pollen

  • Terms modified by Pollen

  • pollen allergen
  • pollen allergic patient
  • pollen allergy
  • pollen analysis
  • pollen assemblage
  • pollen beetle
  • pollen count
  • pollen data
  • pollen deposition
  • pollen development
  • pollen diagram
  • pollen diet
  • pollen dispersal
  • pollen donor
  • pollen evidence
  • pollen exposure
  • pollen extract
  • pollen flow
  • pollen germination
  • pollen grain
  • pollen immunotherapy
  • pollen limitation
  • pollen limited
  • pollen load
  • pollen mixture
  • pollen morphology
  • pollen mother cell
  • pollen number
  • pollen presentation
  • pollen production
  • pollen quantity
  • pollen receipt
  • pollen record
  • pollen season
  • pollen sensitization
  • pollen size
  • pollen source
  • pollen stratigraphy
  • pollen taxa
  • pollen transfer
  • pollen tube
  • pollen tube growth
  • pollen tubes
  • pollen type
  • pollen vector
  • pollen viability

  • Selected Abstracts

    Fungal biodiversity, pollen morphology and leaf surface of some native species in Egypt

    FEDDES REPERTORIUM, Issue 1 2001
    S. I. I. Abdel-Hafez
    Five native species of the flora of Egypt: Adonis dentata Delile, Ranunculaceae; Papaver dubium L., Papaveraceae; Matthiola longipetala (Vent.) DC., Brassicaceae; Malva parviflora L., Malvaceae; and Erodium laciniatum (Cav.) Willd., Geraniaceae have been investigated morphologically, palynologically and mycologically. The total counts of phyllosphere fungi fluctuated between 223 and 388 colonies/100 leaf segments giving maximum on Malva parviflora followed by Matthiola longipetala, Erodium laciniatum, Papaver dubium and Adonis dentata. The widest spectrum of genera (20) and species (39 and l variety) was recorded on Malva parviflora and the narrowest on Adonis dentata (9, 14). Sixty species and one variety belonging to 27 genera were collected from leaves (24 genera and 56 species and 1 variety) and anthers/pollen (16 genera and 27 species) of the five studied plants with the most frequently species were some members of Alternaria, Cladosporium, Fusarium and Mucor. Members of Aspergillus and Penicillium were prevalent only on leaves of Matthiola longipetala and Malva parviflora, while these members were infrequently recorded on leaf surfaces of Adonis dentata and Papaver dubium. Results revealed that density of hairs on the leaf surface and size of leaf blade, almost seem to be the most reliable factors of the biodiversity of the fungal spores on the studied taxa. On the other hand, reticulate or striate pollen surface had a wider spectrum of fungal biodiversity and higher densities of spores compared with echinate and scabrate surface. Pilz-Biodiversität, Pollen-Morphologie und die Blattoberfläche einiger einheimischer Arten in Ágypten Aus der Flora Ágyptens wurden die fünf einheimischen Arten Adonis dentata Delile, Ranunculaceae; Papaver dubium L., Papaveraceae; Matthiola longipetala (Vent.) DC., Brassicaceae; Malva parviflora L., Malvaceae; und Erodium laciniatum (Cav.) Willd., Geraniaceae morphologisch, palynologisch und mykologisch untersucht. Die Gesamtzahl an phyllosphären Pilzen schwankte zwischen 223 und 388 Kolonien/100 Blattsegementen. Das Maximum lag bei Malva parviflora, gefolgt von Matthiola longipetala, Erodium laciniatum, Papaver dubium und Adonis dentata. Das größte Spektrum an Gattungen (20) und Arten (39 und 1 Varietät) wurde bei Malva parviflora verzeichnet, das Minimum hingegen bei Adonis dentata (9, 14). An den fünf Arten wurden insgesamt 60 Arten und eine Varietät aus 27 Gattungen an Blättern (24 Gattungen, 56 Arten und eine Varietät) und Antheren/Pollen (16 Gattungen, 27 Arten) verzeichnet. Die häufigsten Arten gehörten zu den Gattungen Alternaria, Cladosporium, Fusarium und Mucor. Arten von Aspergillus und Penicillium wurden nur an Blättern von Matthiola longipetala und Malva parviflora nachgewiesen, während sie an den Blattoberflächen von Adonis dentata und Papaver dubium seltener waren. Aus den erzielten Resultaten ergibt sich, dass die Dichte des Haarbesatzes an der Blattoberfläche und die Größe der Blattspreite die entscheidenden Faktoren zur Biodiversität der Pilzsporen an den untersuchten Taxa sind. Anderseits kann man sagen, dass reticulate und striate Pollen im Vergleich zu einer echinaten und skabraten Oberfläche ein größeres Spektrum der Pilz-Biodiversität und eine höhere Sporendichte aufwiesen. [source]

    Pollen types of the Egyptian species of the genus Salvia (Lamiaceae)

    FEDDES REPERTORIUM, Issue 7-8 2009
    N. Hassan
    Pollen morphology of seven species of genus Salvia (Lamiaceae) was investigated using light and scanning electron microscopy. Pollen was studied to show all possible characteristic features like shape, size, apertures, wall stratification, etc., with special reference to the specific characters of each pollen type. Four pollen types were recognized viz. Salvia aegyptiaca pollen type, Salvia deserti pollen type, Salvia palaestina pollen type and Salvia spinosa pollen type. Description of each type, a key to the investigated taxa as well as SEM micrographs of pollen types are provided. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    University of San Diego palynological investigation of the Dos Cabezas giants

    P. S. Geyer
    Abstract Beginning in 1999, coprolite soil samples were collected from the skeletal remains of Moche giants excavated at the archaeological site of Dos Cabezas, northern Peru. In 2000, a pilot palynological study was undertaken to ascertain if pollen was recoverable from them. The results of this study encouraged us to form a student team to continue the laboratory research. It was also decided to sample as many of the excavated skeletal remains from the giants' tombs as possible. Following the 2001 field season a palynological study was performed on the three individuals (one adult giant and two children) recovered from Tomb 3 in 1999. Pollen was extracted and analysed. The combined results of this archaeobotanical study are significant and in one instance have led us into insights into the possible causes of death of these three contemporaneous internments. This report represents only the preliminary results of this ongoing research. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Water Deficit Reduced Fertility of Young Microspores Resulting in a Decline of Viable Mature Pollen and Grain Set in Rice

    G. N. Nguyen
    Abstract Pollen formation in rice (Oryza sativa L.) is highly vulnerable to environmental stresses such as heat, chilling and drought. In rice plants exposed to drought during male reproductive development, the most obvious damage often observed is a decline in the number of engorged pollen and grain set. This has been well characterized in rice under chilling and to a lesser extent under drought stress. Moreover, detailed literature on the immediate effects of drought on developing young microspores in rice is still limited. Here, we report findings from experiments on rice plants exposed to water deficit for three consecutive days during early stages of anther development. When the osmotic potential of the growing medium was equal to or less than ,0.5 MPa, as induced by polyethylene glycol, the leaf water potential was significantly lowered and grain set was reduced. A strong correlation between grain set and viable young microspores (P < 0.001, r2 = 0.8223) indicates that water deficit immediately reduced fertility of rice plants at the time of exposure. This result suggests a new underlying mechanism of water deficit-induced pollen abortion in rice. [source]

    Pollen,plant,climate relationships in sub-Saharan Africa

    Julie Watrin
    Abstract Aim, To demonstrate that incorporating the bioclimatic range of possible contributor plants leads to improved accuracy in interpreting the palaeoclimatic record of taxonomically complex pollen types. Location, North Tropical Africa. Methods, The geographical ranges of selected African plants were extracted from the literature and geo-referenced. These plant ranges were compared with the pollen percentages obtained from a network of surface sediments. Climate-response surfaces were graphed for each pollen taxon and each corresponding plant species. Results, Several patterns can be identified, including taxa for which the pollen and plant distributions coincide, and others where the range limits diverge. Some pollen types display a reduced climate range compared with that of the corresponding plant species, due to low pollen production and/or dispersal. For other taxa, corresponding to high pollen producers such as pioneer taxa, pollen types display a larger climatic envelope than that of the corresponding plants. The number of species contained in a pollen taxon is an important factor, as the botanical species included in a taxon may have different geographical and climate distributions. Main conclusions, The comparison between pollen and plant distributions is an essential step towards more precise vegetation and climate reconstructions in Africa, as it identifies taxa that have a high correspondence between pollen and plant distribution patterns. Our method is a useful tool to reassess biome reconstructions in Africa and to characterize accurately the vegetation and climate conditions at a regional scale, from pollen data. [source]

    Late-glacial and Holocene palaeovegetation zonal reconstruction for central and north-central North America

    W. L Strong
    Abstract Aim, The purpose of this study is to develop palaeovegetation zonation models for central and north-central North America, based on late-Quaternary and Holocene pollen stratigraphic data (n = 246 sites). A secondary purpose was to evaluate an hypothesis (Strong & Hills, 2003) to explain the disjunct distribution of species in western Alberta. Location, Hudson Bay-Lake Michigan to the Rocky Mountains region, north of 36° N to the Arctic Ocean (c. 70° N). Methods, Pollen profiles spanning 40 years of palaeoecological research in North America were extracted from published and unpublished archival sources. Individual profiles were subdivided into 1000-year increments based on the assumption of a constant sedimentation rate between stratigraphic dates (e.g. surface sediments, radiocarbon 14C dates, tephra layers). The pollen composition among profiles was standardized to 54 commonly recognized taxa, with percentage composition within each stratigraphic sample prorated to 100% prior to analysis. Near-surface sediments from these profiles were included as analogues of modern vegetation. Cluster analysis was used as a guide to the classification of 2356 temporal stratigraphic samples, which resulted in the recognition of 16 pollen groups. These groups were summarized in terms of their pollen composition, mapped, and used in combination with terrain information and an ecological knowledge of the study area to construct six physiognomically-based palaeovegetation zonation models at 2000-year intervals from 14,000 to 4000 yr bp (radiocarbon years before present). Results, The 14,000 yr bp model placed Boreal and Cordilleran Forests proximal to the southern glacial front, whereas Arctic tundra dominated the Yukon Territory,Alaska ice-free zone. Pollen and macrofossil evidence suggests that this Boreal Forest zone contained a mixture of coniferous and deciduous tree species. Grassland was postulated immediately south of the forest zone, with its northern extreme near 49° N latitude in the Alberta,Montana border area. Separation of the Laurentide and Cordilleran glacial fronts about 12,000 yr bp initiated the northward advance of Boreal Forests into western Canada. By the end of the Hypsithermal at about 6000 yr bp, Boreal Forests occurred near the Arctic Ocean, and Grassland and Aspen Parkland zones may have extended to 54° N and 59° N latitude in Alberta, respectively. Between 6000 and 4000 yr bp, a 5° and 1° latitudinal southward shift of the northern Boreal Forest and Grassland/Aspen Parkland boundaries occurred, respectively, near their contemporary positions with corresponding expansions of the Subarctic and Arctic zones. Modern Canadian Cordilleran Forests along the eastern slopes of the Rocky Mountains were interpreted as originating from the north-central Montana,south-western Alberta area. Jack pine (Pinus banksiana Lamb.), a common Boreal Forest species, appears to have entered central Canada via the north side of Lake Superior after 11,000 yr bp. Main conclusions, Modern vegetation in central Canada evolved from biomes located in the northern USA during the late-Quaternary. The Boreal Forest biome contained the same arboreal taxa as the modern vegetation, except it lacked jack pine. The proposed regional palaeovegetation models support the hypothesis of Strong & Hills (2003), but new independent palaeoecological data will be needed for a proper evaluation. [source]

    Pollen-based reconstructions of biome distributions for Australia, Southeast Asia and the Pacific (SEAPAC region) at 0, 6000 and 18,000 14C yr BP

    Elizabeth J. Pickett
    Abstract Aim, This paper documents reconstructions of the vegetation patterns in Australia, Southeast Asia and the Pacific (SEAPAC region) in the mid-Holocene and at the last glacial maximum (LGM). Methods, Vegetation patterns were reconstructed from pollen data using an objective biomization scheme based on plant functional types. The biomization scheme was first tested using 535 modern pollen samples from 377 sites, and then applied unchanged to fossil pollen samples dating to 6000 ± 500 or 18,000 ± 1000 14C yr bp. Results, 1. Tests using surface pollen sample sites showed that the biomization scheme is capable of reproducing the modern broad-scale patterns of vegetation distribution. The north,south gradient in temperature, reflected in transitions from cool evergreen needleleaf forest in the extreme south through temperate rain forest or wet sclerophyll forest (WSFW) and into tropical forests, is well reconstructed. The transitions from xerophytic through sclerophyll woodlands and open forests to closed-canopy forests, which reflect the gradient in plant available moisture from the continental interior towards the coast, are reconstructed with less geographical precision but nevertheless the broad-scale pattern emerges. 2. Differences between the modern and mid-Holocene vegetation patterns in mainland Australia are comparatively small and reflect changes in moisture availability rather than temperature. In south-eastern Australia some sites show a shift towards more moisture-stressed vegetation in the mid-Holocene with xerophytic woods/scrub and temperate sclerophyll woodland and shrubland at sites characterized today by WSFW or warm-temperate rain forest (WTRF). However, sites in the Snowy Mountains, on the Southern Tablelands and east of the Great Dividing Range have more moisture-demanding vegetation in the mid-Holocene than today. South-western Australia was slightly drier than today. The single site in north-western Australia also shows conditions drier than today in the mid-Holocene. Changes in the tropics are also comparatively small, but the presence of WTRF and tropical deciduous broadleaf forest and woodland in the mid-Holocene, in sites occupied today by cool-temperate rain forest, indicate warmer conditions. 3. Expansion of xerophytic vegetation in the south and tropical deciduous broadleaf forest and woodland in the north indicate drier conditions across mainland Australia at the LGM. None of these changes are informative about the degree of cooling. However the evidence from the tropics, showing lowering of the treeline and forest belts, indicates that conditions were between 1 and 9 °C (depending on elevation) colder. The encroachment of tropical deciduous broadleaf forest and woodland into lowland evergreen broadleaf forest implies greater aridity. Main conclusions, This study provides the first continental-scale reconstruction of mid-Holocene and LGM vegetation patterns from Australia, Southeast Asia and the Pacific (SEAPAC region) using an objective biomization scheme. These data will provide a benchmark for evaluation of palaeoclimate simulations within the framework of the Palaeoclimate Modelling Intercomparison Project. [source]

    A reconstruction of the history of a Holocene sand dune on Great Barrier Island, northern New Zealand, using pollen and phytolith analyses

    M. Horrocks
    Abstract Aim, To reconstruct the history of a Holocene sand dune using pollen and phytolith analyses, and to identify the strengths, weaknesses and compatibility of these two methods in the interpretation of Quaternary coastal environments. Location, Great Barrier Island, northern New Zealand. Methods, Pollen and phytolith analyses were carried out on a sequence through a Holocene sand dune containing a palaeosol. Results, Phytoliths were present throughout the sequence. Grass phytoliths increased at the expense of tree phytoliths following fire disturbance. Pollen (and spores) was preserved only in the palaeosol part of the profile. Pteridium fern spores increased at the expense of tall tree pollen following the fire disturbance. Main conclusions, Lack of phytolith production by many species and problems of taxonomic specificity in many others restricts the usefulness of phytolith analysis to defining only broad vegetation types. In New Zealand, gymnosperms are invisible in the phytolith record and ferns are extremely under-represented. In contrast, pollen analysis usually provides a great deal of information regarding the composition of a particular vegetation type. The loss of microscopic charcoal fragments during the phytolith extraction process is a disadvantage in the reconstruction of environments where fires have occurred. The greater durability of phytoliths compared with pollen means that phytoliths may be found in sediments where pollen has not been preserved. The phytolith record may also provide evidence of wetter environments that are not apparent in the pollen record. Unlike grass pollen, which is widely dispersed and therefore blurs the spatial record, the presence of grass phytoliths in sediments indicates a local source. The simultaneous application of both methods potentially provides a powerful tool in ecological interpretation and the reconstruction of Quaternary coastal environments. [source]

    Pollen-based biomes for Beringia 18,000, 6000 and 0 14C yr bp,

    M. E. Edwards
    Abstract The objective biomization method developed by Prentice et al. (1996) for Europe was extended using modern pollen samples from Beringia and then applied to fossil pollen data to reconstruct palaeovegetation patterns at 6000 and 18,000 14C yr bp. The predicted modern distribution of tundra, taiga and cool conifer forests in Alaska and north-western Canada generally corresponds well to actual vegetation patterns, although sites in regions characterized today by a mosaic of forest and tundra vegetation tend to be preferentially assigned to tundra. Siberian larch forests are delimited less well, probably due to the extreme under-representation of Larix in pollen spectra. The biome distribution across Beringia at 6000 14C yr bp was broadly similar to today, with little change in the northern forest limit, except for a possible northward advance in the Mackenzie delta region. The western forest limit in Alaska was probably east of its modern position. At 18,000 14C yr bp the whole of Beringia was covered by tundra. However, the importance of the various plant functional types varied from site to site, supporting the idea that the vegetation cover was a mosaic of different tundra types. [source]

    Vegetation dynamics in western Uganda during the last 1000 years: climate change or human induced environmental degradation?

    Julius B. Lejju
    Abstract A multi-proxy analysis of microfossils from sedimentary records, together with evidence from historical and archaeological data, has provided evidence of vegetation dynamics and human environment interactions in western Uganda for the last 1000 years. Pollen, fungal spores and phytoliths extracted from sediment cores obtained from a papyrus swamp at Munsa archaeological site indicate a relatively wet and forested environment in western Uganda prior to ca 1000 yr bp (cal 977,1159 ad). A subsequent decline in forest vegetation occurred from ca 920 yr bp (cal 1027,1207 ad). However, the deforestation period occurred during a wet period as registered in the River Nile water records, suggesting a human induced deforestation at Munsa rather than reduced precipitation. Increased numbers of herbivores, presumably domesticated cattle, postdeforestation are evidenced by the presence of dung fungal spores and broad accord with the archaeological evidence for initial occupation of the site at Munsa and the establishment of a mixed economy based on crops, cattle and iron working between 1000 and 1200 ad. From ca 200 yr bp (cal 1647,1952 ad), forest recovery occurred at Munsa site and appears to reflect abandonment of the site, as suggested by archaeological evidence, possibly following a period of prolonged drought and famine between 1600 and 1800 ad, as recounted in the oral rich traditions of western Uganda and also reflected by low water levels of River Nile. [source]

    Pollen and sperm heteromorphism: convergence across kingdoms?

    I. Till-Bottraud
    Abstract Sperm competition theory predicts that males should produce many, similar sperm. However, in some species of animals and plants, males exhibit a heteromorphism that results in the production of at least two different types of sperm or pollen grains. In animals, sperm heteromorphism typically corresponds to the production of one fertile morph and one (or more) sterile morph(s), whereas in plants two or more pollen morphs (one of which can be either sterile or fertile) are produced in all flowers but sometimes in different anthers. Heteromorphism has arisen independently several times across phyla and at different phylogenetic levels. Here, we compare and contrast sperm and pollen heteromorphism and discuss the evolutionary hypotheses suggested to explain heteromorphism in these taxa. These hypotheses include facilitation, nutritive contribution, blocking, cheap filler, sperm flushing or killing for animals; outcrossing and precise cross-pollen transfer or bet-hedging strategy for plants; cryptic female choice for both. We conclude that heteromorphism in the two phyla is most likely linked to a general evolutionary response to sexual selection, either to increase one male's sperm or pollen success in competition with other males, or mediate male/female interactions. Therefore, although sperm and pollen are not homologous, we suggest that heteromorphism represents an example of convergence across kingdoms. [source]

    Fire and vegetation history on Santa Rosa Island, Channel Islands, and long-term environmental change in southern California,

    R. Scott Anderson
    Abstract The long-term history of vegetation and fire was investigated at two locations , Soledad Pond (275,m; from ca. 12 000,cal. a BP) and Abalone Rocks Marsh (0,m; from ca. 7000,cal. a BP) , on Santa Rosa Island, situated off the coast of southern California. A coastal conifer forest covered highlands of Santa Rosa during the last glacial, but by ca. 11 800,cal. a BP Pinus stands, coastal sage scrub and grassland replaced the forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150,cal. a BP, as the pond dried frequently, and coastal sage scrub covered the nearby hillslopes. By ca. 6900,cal. a BP grasslands recovered at both sites. Pollen of wetland plants became prominent at Soledad Pond after ca. 4500,cal. a BP, and at Abalone Rocks Marsh after ca. 3465,cal. a BP. Diatoms suggest freshening of the Abalone Rocks Marsh somewhat later, probably by additional runoff from the highlands. Introduction of non-native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the record, but declines during the early Holocene when minimal biomass suggests extended drought. A general increase occurs after ca. 7000,cal. a BP, and especially after ca. 4500,cal. a BP. The Holocene pattern closely resembles population levels constructed from the archaeological record, and suggests a potential influence by humans on the fire regime of the islands, particularly during the late Holocene. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    A high-resolution pollen and geochemical analysis of late Holocene human impact and vegetation history in southern Cumbria, England,

    Paul M. V. Coombes
    Abstract The historic era, which in Cumbria begins with the Roman invasion of AD 71, is a frequently neglected period in palaeoecological research, but its study can bring benefits in improving knowledge of landscape history and in understanding the significance and limitations of palaeoecological records. Pollen and geochemical data are presented for late Holocene records from Deer Dyke and Hulleter Mosses in southern Cumbria. The records show initially low levels of anthropogenic impact, followed by a phase of forest clearance and mixed agriculture from the 7th to 11th centuries AD. The timing of these clearances suggests that they were initially Anglo-Saxon in origin, rather than Norse. Further clearances in the 16th century AD are interpreted as a response to monastic dissolution and late Tudor population pressures; the landscapes reached their contemporary form following extensive clearances in the 17th century AD. Silicon and titanium concentrations at Deer Dyke Moss were used to reconstruct past levels of atmospheric dust loading, which is broadly related to soil erosion. Geochemical influx was found to peak during periods of landscape transition rather than from established land use. This relationship with pollen data is thought to reflect the predominantly low levels of anthropogenic impact in the region, which changes as substantial woodland clearances during the 16th century AD and continuous land use pressure since then have greatly increased the supply of airborne dust. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Climatic change during the last 4000 years in the southern Tarim Basin, Xinjiang, northwest China,

    Wei Zhong
    Abstract In this study, a ca. 4000,cal. yr ancient lacustrine (or wetland) sediment record at the southern margin of Tarim Basin is used to reconstruct the history of climate change. Six radiocarbon dates on organic matter were obtained. ,18O and ,13C of carbonate, pollen and sediment particle size were analysed for climate proxies. The proxies indicate that a drier climate prevailed in the area before ca. 1010 BC and during period 1010 BC,AD 500 climate then changed rapidly and continuously from dry to moist, but after about AD 500 climate generally shows dry condition. Several centennial-scale climatic events were revealed, with the wettest spell during AD 450,550, and a relatively wetter interval between AD 930,1030. Pollen results show that regional climate may influence human agricultural activities. Spectral analysis of mean grain size (MGS) proxy reveals statistically pronounced cyclic signals, such as ca. 200,yr, ca. 120,yr, ca. 90,yr, ca. 45,yr and ca. 33 or 30,yr, which may be associated with solar activities, implying that solar variability plays an important role in the decadal- and centennial-scale climate variations in the study area. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    The Holocene shore displacement of Gästrikland, eastern Sweden: a contribution to the knowledge of Scandinavian glacio-isostatic uplift,

    Mikael Berglund
    Abstract The shore displacement in Gästrikland, east-central Sweden, has been investigated by means of AMS radiocarbon dating of sediment cores from isolated basins. Twenty dates from 11 sites are presented. Pollen and diatom analyses, and archive material from the Geological Survey of Sweden, have been used to identify isolation intervals in the cores and as chronological support to the 14C dates. An important pollen stratigraphical time-marker is a distinct mid-Holocene increase in Tilia. For the mid-Holocene, pollen stratigraphy is used rather than the 14C dates for the age determination. The deglaciation of Gästrikland, according to the new 14C dates, took place ca. 11,000,cal.,yr,BP (ca. 9500 14C,yr,BP). Through the Holocene the shore displacement is regressive. The regression was initially rapid (on average ca. 3.5,m per 100,yr 11,000,7500,cal.,yr,BP, probably much more rapid at the earliest stage), then slowed down considerably and was from ca. 5000,cal.,yr,BP (probably already from 7000,cal.,yr,BP) relatively constant, ca. 0.8,0.9,m per 100,yr. There are important differences between the shore level curve from Gästrikland and curves from other areas, indicating some irregularities in the regional glacio-isostatic rebound. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Pollen- and diatom based environmental history since the Last Glacial Maximum from the Andean core Fúquene-7, Colombia

    Maria Isabel Vélez
    Abstract The late Pleistocene,Holocene ecological and limnological history of Lake Fúquene (2580 m a.s.l.), in the Colombian Andes, is reconstructed on the basis of diatom, pollen and sediment analyses of the upper 7 m of the core Fúquene-7. Time control is provided by 11 accelerator mass spectrometry (AMS) 14C dates ranging from 19 670 ± 240 to 6040 ± 60 yr BP. In this paper we present the evolution of the lake and its surroundings. Glacial times were cold and dry, lake-levels were low and the area was surrounded by paramo and subparamo vegetation. Late-glacial conditions were warm and humid. The El Abra Stadial, a Younger Dryas equivalent, is reflected by a gap in the sedimentary record, a consequence of the cessation of deposition owing to a drop in lake-level. The early Holocene was warm and humid; at this time the lake reached its maximum extension and was surrounded by Andean forest. The onset of the drier climate prevailing today took place in the middle Holocene, a process that is reflected earlier in the diatom and sediment records than in the pollen records. In the late Holocene human activity reduced the forest and transformed the landscape. Climate patterns from the Late-glacial and throughout the Holocene, as represented in our record, are similar to other records from Colombia and northern South America (the Caribbean, Venezuela and Panama) and suggest that the changes in lake-level were the result of precipitation variations driven by latitudinal shifts of the Intertropical Convergence Zone. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Pollen-based biome reconstructions for Colombia at 3000, 6000, 9000, 12 000, 15 000 and 18 000 14C yr ago: Late Quaternary tropical vegetation dynamics

    Robert Marchant
    Abstract Colombian biomes are reconstructed at 45 sites from the modern period extending to the Last Glacial Maximum (LGM). The basis for our reconstruction is pollen data assigned to plant functional types and biomes at six 3000-yr intervals. A reconstruction of modern biomes is used to check the treatment of the modern pollen data set against a map of potential vegetation. This allows the biomes reconstructed at past periods to be assessed relative to the modern situation. This process also provides a check on the a priori assignment of pollen taxa to plant functional types and biomes. For the majority of the sites, the pollen data accurately reflect the potential vegetation, even though much of the original vegetation has been transformed by agricultural practices. At 18 000 14C yr BP, a generally cool and dry environment is reflected in biome, assignments of cold mixed forests, cool evergreen forests and cool grassland,shrub; the latter extending to lower altitudes than presently recorded. This signal is strongly recorded at 15 000 and 12 000 14C yr BP, the vegetation at these times also reflecting a relatively cool and dry environment. At 9000 14C yr BP there is a shift to biomes thought to result from slightly cooler environmental conditions. This trend is reversed by 6000 14C yr BP; most sites, within a range of different environmental settings, recording a shift to more xeric biome types. There is an expansion of steppe and cool mixed-forest biomes, replacing tropical dry forest and cool grassland,shrub biomes, respectively. These changes in biome assignments from the modern situation can be interpreted as a biotic response to mid-Holocene climatic aridity. At 3000 14C yr BP the shift is mainly to biomes characteristic of slightly more mesic environmental conditions. There are a number of sites that do not change biome assignment relative to the modern reconstruction, although the affinities that these sites have to a specific biome do change. These ,anomalies' are interpreted on a site-by-site basis. Spatially constant, but differential response of the vegetation to climatic shifts are related to changes in moisture sources and the importance of edaphic controls on the vegetation. The Late Quaternary reconstruction of large-scale vegetation dynamics in Colombia allows an understanding of the environmental controls on these to be developed. In particular, shifts in the character of the main climatic systems that influence Colombian vegetation are described. Copyright © 2002 John Wiley & Sons, Ltd. [source]

    Integrated marine and terrestrial evidence for abrupt Congo River palaeodischarge fluctuations during the last deglaciation

    Fabienne Marret
    Abstract We present a high-resolution reconstruction of tropical palaeoenvironmental changes for the last deglacial transition (18 to 9 cal. kyr BP) based on integrated oceanic and terrestrial proxies from a Congo fan core. Pollen, grass cuticle, Pediastrum and dinoflagellate cyst fluxes, sedimentation rates and planktonic foraminiferal ,18O ratios, u37K, sea-surface temperature and alkane/alkenone ratio data highlight a series of abrupt changes in Congo River palaeodischarge. A major discharge pulse is registered at around 13.0 cal. kyr BP which we attribute to latitudinal migration of the Intertropical Convergence Zone (ITCZ) during deglaciation. The data indicate abrupt and short-lived changes in the equatorial precipitation regime within a system of monsoonal dynamics forced by precessional cycles. The phases of enhanced Congo discharge stimulated river-induced upwelling and enhanced productivity in the adjacent ocean. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Exposure to cadmium-contaminated soils increases allergenicity of Poa annua L. pollen

    ALLERGY, Issue 10 2010
    R. Aina
    To cite this article: Aina R, Asero R, Ghiani A, Marconi G, Albertini E, Citterio S. Exposure to cadmium-contaminated soils increases allergenicity of Poa annua L. pollen. Allergy 2010; 65: 1313,1321. Abstract Background:, Pollution is considered as one main cause for the increase of allergic diseases. Air pollutants may cause and worsen airway diseases and are probably able to make pollen allergens more aggressive. Previous studies looked at traffic-related air pollution, but no data about the effects of polluted soils on pollen allergens are available. We aimed to assess the effects of plant exposure to cadmium-contaminated soil on allergenicity of the annual blue grass, Poa annua L, pollen. Methods:,Poa plants were grown in soil contaminated or not contaminated (control) with cadmium. At flowering, mature pollen was analyzed by microscopy, to calculate the percentage of pollen grains releasing cytoplasmic granules, and by proteomic techniques to analyze allergen proteins. Allergens were identified by sera from grass pollen,allergic patients and by mass spectrometry. Results:, Pollen from Cd-exposed plants released a higher amount of allergenic proteins than control plants. Moreover, Cd-exposed pollen released allergens-containing cytoplasmic grains much more promptly than control pollen. Group 1 and 5 allergens, the major grass pollen allergens, were detected both in control and Cd-exposed extracts. These were the only allergens reacting with patient's sera in control pollen, whereas additional proteins strengthening the signal in the gel region reacting with patient's sera were present in Cd-exposed pollen. These included a pectinesterase, a lipase, a nuclease, and a secretory peroxydase. Moreover, a PR3 class I chitinase-like protein was also immunodetected in exposed plants. Conclusion:, Pollen content of plants grown in Cd-contaminated soils is more easily released in the environment and also shows an increased propensity to bind specific IgE. [source]

    The allergen Bet v 1 in fractions of ambient air deviates from birch pollen counts

    ALLERGY, Issue 7 2010
    J. T. M. Buters
    To cite this article: Buters JTM, Weichenmeier I, Ochs S, Pusch G, Kreyling W, Boere AJF, Schober W, Behrendt H. The allergen Bet v 1 in fractions of ambient air deviates from birch pollen counts. Allergy 2010; 65: 850,858. Abstract Background:, Proof is lacking that pollen count is representative for allergen exposure, also because allergens were found in nonpollen-bearing fractions of ambient air. Objective:, We monitored simultaneously birch pollen and the major birch pollen allergen Bet v 1 in different size fractions of ambient air from 2004 till 2007 in Munich, Germany. Methods:, Air was sampled with a ChemVol® high-volume cascade impactor equipped with stages for particulate matter (PM)>10 ,m, 10 ,m>PM>2.5 ,m, and 2.5 ,m>PM>0.12 ,m. Allergen was determined with a Bet v 1-specific ELISA. Pollen count was assessed with a Burkard pollen trap. We also measured the development of allergen in pollen during ripening. Results:, About 93 ± 3% of Bet v 1 was found in the PM,>,10 ,m fraction, the fraction containing birch pollen. We did not measure any Bet v 1 in 2.5 ,m,>,PM,>,0.12 ,m. Either in Munich no allergen was in this fraction or the allergen was absorbed to diesel soot particles that also deposit in this fraction. Pollen released 115% more Bet v 1 in 2007 than in 2004. Also within 1 year, the release of allergen from the same amount of pollen varied more than 10-fold between different days. This difference was explained by a rapidly increasing expression of Bet v 1 in pollen in the week just before pollination. Depending on the day the pollen is released during ripening, its potency varies. Conclusion:, In general, pollen count and allergen in ambient air follow the same temporal trends. However, because a 10-fold difference can exist in allergen potency of birch pollen, symptoms might be difficult to correlate with pollen counts, but perhaps better with allergen exposure. [source]

    Detection of pollen grains in multifocal optical microscopy images of air samples

    Sander H. Landsmeer
    Abstract Pollen is a major cause of allergy and monitoring pollen in the air is relevant for diagnostic purposes, development of pollen forecasts, and for biomedical and biological researches. Since counting airborne pollen is a time-consuming task and requires specialized personnel, an automated pollen counting system is desirable. In this article, we present a method for detecting pollen in multifocal optical microscopy images of air samples collected by a Burkard pollen sampler, as a first step in an automated pollen counting procedure. Both color and shape information was used to discriminate pollen grains from other airborne material in the images, such as fungal spores and dirt. A training set of 44 images from successive focal planes (stacks) was used to train the system in recognizing pollen color and for optimization. The performance of the system has been evaluated using a separate set of 17 image stacks containing 65 pollen grains, of which 86% was detected. The obtained precision of 61% can still be increased in the next step of classifying the different pollen in such a counting system. These results show that the detection of pollen is feasible in images from a pollen sampler collecting ambient air. This first step in automated pollen detection may form a reliable basis for an automated pollen counting system. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source]

    Realized gene flow within mixed stands of Quercus robur L. and Q. petraea (Matt.) L. revealed at the stage of naturally established seedling

    MOLECULAR ECOLOGY, Issue 10 2010
    Abstract The estimates of contemporary gene flow assessed based on naturally established seedlings provide information much needed for understanding the abilities of forest tree populations to persist under global changes through migration and/or adaptation facilitated by gene exchange among populations. Here, we investigated pollen- and seed-mediated gene flow in two mixed-oak forest stands (consisting of Quercus robur L. and Q. petraea [Matt.] Liebl.). The gene flow parameters were estimated based on microsatellite multilocus genotypes of seedlings and adults and their spatial locations within the sample plots using models that attempt to reconstruct the genealogy of the seedling cohorts. Pollen and seed dispersal were modelled using the standard seedling neighbourhood model and a modification,the 2-component seedling neighbourhood model, with the later allowing separation of the dispersal process into local and long-distance components. The 2-component model fitted the data substantially better than the standard model and provided estimates of mean seed and pollen dispersal distances accounting for long-distance propagule dispersal. The mean distance of effective pollen dispersal was found to be 298 and 463 m, depending on the stand, while the mean distance of effective seed dispersal was only 8.8 and 15.6 m, which is consistent with wind pollination and primarily seed dispersal by gravity in Quercus. Some differences observed between the two stands could be attributed to the differences in the stand structure of the adult populations and the existing understory vegetation. Such a mixture of relatively limited seed dispersal with occasional long distance gene flow seems to be an efficient strategy for colonizing new habitats with subsequent local adaptation, while maintaining genetic diversity within populations. [source]

    Partitioning nuclear and chloroplast variation at multiple spatial scales in the neotropical epiphytic orchid, Laelia rubescens

    MOLECULAR ECOLOGY, Issue 9 2004
    Abstract Insights into processes that lead to the distribution of genetic variation within plant species require recognition of the importance of both pollen and seed movement. Here we investigate the contributions of pollen and seed movement to overall gene flow in the Central American epiphytic orchid, Laelia rubescens. Genetic diversity and structure were examined at multiple spatial scales in the tropical dry forest of Costa Rica using nuclear (allozymes) and chloroplast restriction fragment length polymorphism (RFLP) markers, which were found to be diverse (allozymes, P = 73.3%; HE = 0.174; cpDNA, HE = 0.741). Nuclear genetic structure (FSTn) was low at every spatial scale (0.005,0.091). Chloroplast markers displayed more structure (0.073,0.254) but relatively similar patterns. Neither genome displayed significant isolation-by-distance. Pollen and seed dispersal rates did not differ significantly from one another (mp/ms = 1.40) at the broadest geographical scale, among sites throughout Costa Rica. However, relative contributions of pollen and seeds to gene flow were scale-dependent, with different mechanisms determining the dominant mode of gene flow at different spatial scales. Much seed dispersal is highly localized within the maternal population, while some seeds enter the air column and are dispersed over considerable distances. At the intermediate scale (10s to 100s of metres) pollinators are responsible for substantial pollen flow. This species appears capable of distributing its genes across the anthropogenically altered landscape that now characterizes its Costa Rican dry forest habitat. [source]

    Barremian Angiosperm Pollen and Associated Palynomorphs from the Dakhla Oasis Area, Egypt

    PALAEONTOLOGY, Issue 1 2002
    Eckart Schrank
    Pollen grains characteristic of the local pre-tricolpate, pre-Aptian phase of angiosperm evolution have been recovered from the upper part of the Six Hills Formation in the Dakhla Oasis area, Egypt. Highest abundance (up to 16.5 per cent) and diversity of angiosperm pollen is attained in samples from the Tineida 2 borehole, which also display a remarkable variety of different aperture types for a palynoflora of late Barremian age. Monosulcate, columellate tectates such as Retimonocolpites are most important, but a single trichotomosulcate grain as well as monoporate and inaperturate types that have not been reported from many coeval palynofloras, are also present. The following new taxa are described using same-grain SEM/LM techniques: Tucanopollis annulatus Schrank, sp. nov., Retimonocolpites pennyi Schrank and Mahmoud, sp. nov. and Retiacolpites columellatus Schrank, gen. et sp. nov. Phytogeographic links are closest with palynofloras previously described from the late Barremian of West Africa (Gabon, Congo), that is within the Northern Gondwana or Dicheiropollis etruscus/Afropollis Province. [source]

    In Vitro Toxicity towards Kiwifruit Pollen of the Antimicrobial Peptides Magainins 1 and 2

    PLANT BIOLOGY, Issue 6 2007
    A. M. Speranza
    Abstract: In vitro toxicity of the antimicrobial peptides (AMPs) magainin 1 and 2 to a higher plant organism, i.e., the bicellular male gametophyte of Actinidia deliciosa (kiwifruit), is investigated. Heavy damage to the plasma membrane, the primary cellular target of the peptides, was rapidly induced: in as few as 15 min, from 70 to nearly 100 % of pollen grains were rendered unviable by 20 ,M magainin 1 or 2, respectively. Therefore, kiwifruit pollen sensitivity to natural magainins seemed to be higher if compared to the sensitivity of other pollen species towards magainin 2 amide or synthetic magainin analogues. Strong dose-dependent inhibitory effects on kiwifruit pollen performance were registered: as for magainin 1, the EC50 at 120 min varied from 14.0 (germination) to 15.8 ,M (tube elongation). The inhibitory effect was much greater when administering magainin 1 to elongating tubes rather than to ungerminated pollen grains. The two peptides differentially affected kiwifruit pollen, in line with the previously documented greater activity of magainin 2 in other cell systems. Furthermore, 20 ,M magainin 1-treated pollen grains took on a shrivelled shape within 30 min of incubation, an increasingly widespread effect with higher peptide concentration. At the ultrastructural level, both protoplast shrinkage and striking organelle alterations were evident, including chromatin condensation, swelling and loss of mitochondrial cristae, dilation of rough endoplasmic reticulum cisternae, and vacuolization of cytoplasm. To our knowledge, similar alterations in animal or plant cells treated with AMPs have not been described yet. [source]

    Breeding behavior and its possible consequences for gene flow in Taraxacum sect.

    Erythrosperma (H. Lindb.) Dahlst.
    Abstract Studies of pollen, seed set and experimental hybridizations were carried out to clarify breeding behavior and gene flow pathways in Taraxacum sect. Erythrosperma. Seeds from hybridization (106 samples), open pollinated (34) and bagged (43) capitula were analyzed for breeding system using a flow,cytometric seed screen. In the section Erythrosperma, diploids are obligate sexuals, mostly allogamous; however, autogamy also occurs (in 28% of unpollinated capitula). Triploids are apomicts with residual sexuality (in 13% of capitula pollinated by pollen of diploids). Pollen of diploids in Taraxacum is usually approximately the same size (regular pollen). In our study, in the section Erythrosperma, many diploids (24%) produced pollen grains of different sizes (irregular pollen) and one plant produced no pollen. The pollen of triploids is either irregular (33%) or the triploids produce no pollen (67%). Consequently, the method of ploidy level assessment on the basis of pollen characteristics is not suitable for Taraxacum sect. Erythrosperma. Low potential for polyploid hybrid formation between diploid maternal plants and polyploid pollen donors, considerable tendency to autogamy and no evidence of the formation of diploid progeny by polyploid maternal plants (facultative apomixis) indicates low intensity of gene flow within Taraxacum sect. Erythrosperma. This, together with a lower population density and spatial isolation of ploidy levels, is expected to result in a lower rate of formation of new apomictic lineages. Thus, Taraxacum sect. Erythrosperma appears evolutionarily more stable and taxonomically less complicated than sect. Ruderalia. The present study supports the agamospecies concept of Taraxacum sect. Erythrosperma. [source]

    Male gametophyte development in bread wheat (Triticum aestivum L.): molecular, cellular, and biochemical analyses of a sporophytic contribution to pollen wall ontogeny

    THE PLANT JOURNAL, Issue 6 2002
    Aiming Wang
    Summary Bread wheat (hexaploid AABBDD genome; 16 billion basepairs) is a genetically complex, self-pollinating plant with bisexual flowers that produce short-lived pollen. Very little is known about the molecular biology of its gametophyte development despite a longstanding interest in hybrid seeds. We present here a comprehensive characterization of three apparently homeologous genes (TAA1a, TAA1b and TAA1c) and demonstrate their anther-specific biochemical function. These eight-exon genes, found at only one copy per haploid complement in this large genome, express specifically within the sporophytic tapetum cells. The presence of TAA1 mRNA and protein was evident only at specific stages of pollen development as the microspore wall thickened during the progression of free microspores into vacuolated-microspores. This temporal regulation matched the assembly of wall-impregnated sporopollenin, a phenylpropanoid-lipid polymer containing very long chain fatty alcohols (VLCFAlc), described in the literature. Our results establish that sporophytic genes contribute to the production of fatty alcohols: Transgenic expression of TAA1 afforded production of long/VLCFAlc in tobacco seeds (18 : 1; 20 : 1; 22 : 1; 24 : 0; 26 : 0) and in Escherichia coli (14 : 0; 16 : 0; 18 : 1), suggesting biochemical versatility of TAA1 with respect to cellular milieu and substrate spectrum. Pollen walls additionally contain fatty alcohols in the form of wax esters and other lipids, and some of these lipids are known to play a role in the highly specific sexual interactions at the pollen,pistil interface. This study provides a handle to study these and to manipulate pollen traits, and, furthermore, to understand the molecular biology of fatty alcohol metabolism in general. [source]

    Impacts of hive honeybees on Tasmanian leatherwood Eucryphia lucida Labill. (Eucryphiaceae)

    AUSTRAL ECOLOGY, Issue 2 2009
    Abstract Despite honeybees (Apis mellifera L.) occurring as a feral and commercially managed species in many parts of Australia, the effects of honeybees on native Australian ecosystems are poorly understood. We examined the impacts of honeybee apiaries on Tasmanian Leatherwood Eucryphia lucida Labill. (Eucryphiaceae) by comparing commercial apiary sites with control sites >2 km from the nearest apiary. Feral honeybees were common at control sites (73% of honeybees feral) but were scarce at apiary sites (2%), and hive honeybees appeared to be competitively displacing feral honeybees near apiaries. Visit rates by native insects appeared to be un-affected by the increased numbers of hive honeybees near apiaries. Standing crops of nectar sugar were significantly depressed at apiary sites. Pollen was rapidly removed from flowers at apiary sites resulting in full separation of the male and female flower-phases (flowers completely dichogamous). In contrast, at control sites, pollen tended to remain in flowers into the female phase (flowers partially dichogamous). There was no difference in the total number of pollen grains deposited on stigmas or in percentage seed set among apiary and control sites. However, fruit set was elevated at apiary sites, possibly owing to reduced autonomous (within-flower) selfing. Our study indicated that honeybees significantly reduce floral resources (nectar and pollen) around apiaries, although any competitive effects on native insects may have been obscured by large variation in the abundance of native insects among experimental sites. [source]

    Reproduction in Wild Populations of the Threatened Tree Macadamia tetraphylla: Interpopulation Pollen Enriches Fecundity in a Declining Species

    BIOTROPICA, Issue 3 2009
    Philip C. Pisanu
    ABSTRACT Macadamia tetraphylla is a subtropical rain forest tree from fragmented lowlands in eastern Australia. Owing to habitat loss and fragmentation, this commercially important species is vulnerable to extinction. Breeding system and fecundity were investigated in nine populations incorporating three habitat types (moderately disturbed, highly disturbed, and intact) to determine if seed set, seed weight, and genetic diversity are compromised by disturbance. Breeding success was also tested using pollen donors from distant (30,100 km), local (2,3 km), neighbor (10,20 m), and near-neighbor (< 10 m) sources. Macadamia tetraphylla is weakly self-compatible but incapable of automatic self-pollination. Across populations, seed to flower ratios were always < 0.1 percent in open-pollinated trees and trees from moderately disturbed habitats had the highest fruit production. Outcross pollen produced more seed per raceme than open-pollinated or self-pollination treatments. Seed set and seed weights were positively influenced by pollen source with local pollen and distant pollen effecting more or heavier seeds. Germination rates and genetic diversity did not vary significantly in seedlings from different pollen sources. Results suggest a pollen source from at least a 2 km distance is an optimal outbreeding distance; however, many wild populations do not have conspecifics at optimal distances owing to habitat fragmentation. Highly disturbed populations are producing seed but the longevity of these sites is threatened by weed invasions. We conclude that small populations in degraded habitats that are at risk of being overlooked should not be ignored but should be a focus for restoration efforts as they are a valuable asset for the conservation of M. tetraphylla. [source]

    Factors affecting pollination ecology of Quercus anemophilous species in north-west Spain

    Pollination ecology of Quercus is influenced by meteorological, biotic and genetic factors. This study was undertaken to ascertain the effect induced by these factors on pollen production, release and dispersion. Aerobiological data have been used in recent years as phenological information, because the presence of pollen in the air is the result of flowering across a wide area. The onset of the Quercus pollen season and the atmospheric pollen concentrations during the pollination period in two localities of north-west Spain (Ourense and Santiago) were determined from 1993 to 2001. There were important variations in total annual pollen as a result of meteorological conditions, lenticular galls produced by Neuropterus on catkins and biennial genetic rhythms of pollen production. In order to determine the beginning of flowering, a thermal time model has been used. Chill requirements were around 800 chilling hours (CH) and heat requirements were 953 growth degree days (GDD in °C) in Santiago and 586 GDD in Ourense. Pollen in the air show positive correlation (99% significance) with daily thermal oscillation, maximum and minimum temperatures, and hours of sunshine. Regression analysis with previous days' pollen concentrations explained the high percentage of pollen concentration variability, as meteorological variables do not, on their own, explain pollen production and release. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 149, 283,297. [source]