Some New Sporomorphs from the Upper Tertiary of Nigeria

A simple model for the immission of pollen grains from large area sources into the atmospheric convective boundary layer is presented.

The terrain is assumed to be homogeneous (like a large plain) and the sources are assumed to be uniform over horizontal distances of the order of 10 km.

The model requires the production rate of pollen to be specified, as well as the temperature as a function of time or analogous atmospheric parameters.

The results compare well with data measured in the Po Valley, Italy.     

Effects of pollen competitive environment on pollen performance in Mirabilis jalapa (Nyctaginaceae)

 We examined the influence of pollen competitive environment on pollen performance in Mirabilis jalapa. We used the number of pollen grains and the number of pollen tubes per pistil as measures of pollen competition. Pollen germination, pollen tube penetration into the style, and pollen tube growth rates were used as measures of pollen performance. All three measures of pollen performance were affected by the competitive environment. Pollen germination was greatest at intermediate pollen load sizes. The percentage of germinated pollen grains that penetrated the stigma and grew into the style decreased with pollen load size. Pollen tube growth rate in the style was greater and more variable with larger numbers of pollen tubes in the style. Controlling for the degree of selection at the stigma indicated that pollen-pollen or pollen-style interactions were the likely causes of increased growth rates. Received: 28 October 1996 / Revision accepted: 24 January 1997     

Pollen morphology and germination inNarcissus

Pollen grains of several species and varieties ofNarcissus were examined with a light microscope and a scanning electron microscope. Normal pollen grains were kidney- or spindle-shaped with a germination furrow and a reticulate structure similar to that of the pollen grains ofAmaryllis. Pollen grains germinated within 2 to 3 hr. Percentage of germination was dependent upon temperature and treatment. Pollen tubes grew in length up to 1,000 μm and branched occasionally or behaved in strange fashion. Fresh pollen grains germinated more in distilled water at lower temperature than in sucrose-aqueous medium. Both in the presence and in the absence of stigmatic exudate calcium increased the percentage of germination. Gibberellic acid, abscisic acid and coumarin inhibited the pollen germination. Plasmoptysis occurred in all species and in all media tested except in a medium containing coumarin without stigmatic exudates. Plasmoptysis did not seem to be induced by hypotonic medium alone. Pollen of high germination capacity showed a high percentage of plasmoptysis. Based on the results obtained, evolution and sterility of theNarcissus plant was discussed.     

Light and electron microscopies reveal unknown details of the pollen grain structure and physiology from Brazilian Cerrado species

Pollen grains have a relatively simple structure and microscopic size, with two or three cells surrounded by the protective sporoderm at maturity. The viability and efficiency of pollen transport from anther to stigma depends on pollen physiological properties, especially the relative water content of the vegetative cell. Pollen transport is a crucial fate for most angiosperms that depends on biotic pollinators and studies focusing on understanding the morpho-physiological properties of pollen grains are still scarce, especially to tropical open physiognomies as the Brazilian Cerrado. Therefore, we investigate some structural and physiological aspects of pollen grains from six native species naturally growing in one Cerrado area: Campomanesia pubescens (Myrtaceae), Caryocar brasiliense (Caryocaraceae), Erythroxylum campestre (Erythroxylaceae), Lippia lupulina (Verbenaceae), Pyrostegia venusta (Bignoniaceae), and Xylopia aromatica (Annonaceae). We selected dehiscent anthers and mature pollen grains to analyze (1) the anther wall and pollen microstructure, (2) the pollen water status at the time of anther dehiscence, and (3) the pollen chemical compounds. In all analyzed species, the anther and pollen developed in a successfully way, and except for Caryocar brasiliense, all species were able to emit pollen tubes in the germination tests. As expected for a dry and open environment, most species dispersed their pollen grains in a partially dehydrated form, as indicated by our harmomegathy experiment. As indicated by our study, the pollen ability in preventing dissection, maintaining its viability in a dry and hot environment during its transport from anther to stigma, may be related to the sporoderm apertures and to the reserve compounds, mainly carbohydrates in the form of hydrolysable starch grains.

     

Pollen Deposition on and under the Water Surface

In the summers of 1974 and 1975 pollen deposition was studied in two bays of the Baltic Sea near Stockholm with roofed and unroofed samplers mounted on rafts and with samplers submerged to levels of 30 and 60 cm over the bottom. The unroofed traps show larger totals of pollen grains than the roofed samplers. Sufficient data could not be obtained to establish that the totals of pollen grains in the submerged samplers at level 30 cm were larger than the totals at level 60 cm. The differences in pollen rain in the two seasons can be attributed mainly to the meteorological conditions, viz, to the particularly dry and warm summer of 1975. In the raft samplers the percentages of redeposited arboreal pollen are lower than in the submerged ones. Transport by currents and redeposition influence the pollen spectra in the submerged samplers. The pollen spectra in samplers over and under the water surface depend mainly on the specific composition of the surrounding vegetation. Pollen transport over short distances is therefore of great importance. No evidence was found of long-distance pollen transport.     

Wind‐mediated horseweed (Conyza canadensis) gene flow: pollen emission,dispersion, and deposition

Horseweed (Conyza canadensis) is a problem weed in crop production because of its evolved resistance to glyphosate and other herbicides. Although horseweed is mainly self-pollinating, glyphosate-resistant (GR) horseweed can pollinate glyphosate-susceptible (GS) horseweed. To the best of our knowledge, however, there are no available data on horseweed pollen production, dispersion, and deposition relative to gene flow and the evolution of resistance. To help fill this knowledge gap, a 43-day field study was performed in Champaign, Illinois, USA in 2013 to characterize horseweed atmospheric pollen emission, dispersion, and deposition. Pollen concentration and deposition, coupled with atmospheric data, were measured in a source field (180 m by 46 m) and its surrounding areas up to 1 km downwind horizontally and up to 100 m vertically. The source strength (emission rate) ranged from 0 to 140 pollen grains per plant per second (1170 to 2.1×10⁶ per plant per day). For the life of the study, the estimated number of pollen grains generated from this source field was 10.5×10¹⁰ (2.3×10⁶ per plant). The release of horseweed pollen was not strongly correlated to meteorological data and may be mainly determined by horseweed physiology. Horseweed pollen reached heights of 80 to100 m, making long-distance transport possible. Normalized (by source data) pollen deposition with distance followed a negative-power exponential curve. Normalized pollen deposition was 2.5% even at 480 m downwind from the source edge. Correlation analysis showed that close to or inside the source field at lower heights (≤3 m) vertical transport was related to vertical wind speed, while horizontal pollen transport was related to horizontal wind speed. High relative humidity prevented pollen transport at greater heights (3–100 m) and longer distances (0–1000 m) from the source. This study can contribute to the understanding of how herbicide-resistance weeds or invasive plants affect ecology through wind-mediated pollination and invasion.     

Precocious pollen germination in Arabidopsis plants with altered callose deposition during microsporogenesis

Pollination is essential for seed reproduction and for exchanges of genetic information between individual plants. In angiosperms, mature pollen grains released from dehisced anthers are transferred to the stigma where they become hydrated and begin to germinate. Pollen grains of wild-type Arabidopsis thaliana do not germinate inside the anther under normal growth conditions. We report two Arabidopsis lines that produced pollen grains able to in situ precociously germinate inside the anther. One of them was a callose synthase 9 (cs9) knockout mutant with a T-DNA insertion in the Callose Synthase 9 gene (CalS9). Male gametophytes carrying a cs9 mutant allele were defective and no homozygous progeny could be produced. Heterozygous mutant plants (cs9/+) produced approximately 50% defective pollen grains with an altered male germ unit (MGU) and aberrant callose deposition in bicellular pollen. Bicellular pollen grains germinated precociously inside the anther. Another line, a transgenic plant expressing callose synthase 5 (CalS5) under the CaMV 35S promoter, also contained abnormal callose deposition during microsporogenesis and displaced MGUs in pollen grains. We also observed that precocious pollen germination could be induced in wild-type plants by incubation with medium containing sucrose and calcium ion and by wounding in the anther. These results demonstrate that precocious pollen germination in Arabidopsis could be triggered by a genetic alteration and a physiological condition.     

Pollen production in the Poaceae family

Total pollen production per inflorescence was studied in the most important species of the Poaceae family in the city of Córdoba in order to further our knowledge of the partial contribution of each species of this family to the total amount of pollen released into the atmosphere.

The contribution of grasses in a given area was estimated by counting the number of inflorescences in an area of one square meter. Four different representative areas of the city were selected. The number of pollen grains per anther and flowers per inflorescence was also estimated in order to obtain total pollen production per inflorescence.

Pollen production per inflorescence ranged from 14,500 to more than 22,000,000 pollen grains, the amount being clearly higher in the perennial species. Pollen production per square meter was higher in the mountains near the city and lower in areas of abandoned crops.

Only a few species are responsible for the majority of pollen produced. A phenological study is necessary in order to determine the temporal distribution of this pollen production and subsequent shedding.     

Modelling analysis of source regions of long-range transported birch pollen that influences allergenic seasons in Lithuania

This study analyses the spatial and temporal distribution of regional and long-range transported birch (Betula L.) pollen in Lithuania and the neighbouring countries. The potential long-range transport cases of birch pollen in Lithuania were analysed for the whole period of available observations, 2004–2007. The birch pollen was recorded at three measurement stations in Lithuania by using Hirst-type volumetric spore traps. The phenological observations in Lithuania were also used for the detection of potential long-range transport-induced episodes. Two variants of the regional and continental scale atmospheric dispersion model SILAM (Lagrangian and Eulerian) in an adjoint mode (used for inverse dispersion modelling and data assimilation), and the trajectory model HYSPLIT were employed to evaluate the source origins of the observed pollen. During four seasons in 2004–2007, we found in total 24 cases, during which remarkable pollen concentrations were recorded before the local flowering season. According to modelling, most of these were originated from the sources outside Lithuania: Latvia, southern Sweden, Denmark, Belarus, Ukraine and Moldova, possibly, also coastal regions of Germany and Poland. Two episodes were attributed to local early-flowering birch trees. The spatial and temporal patterns of the long-range transport of early pollen to Lithuania were found out to be highly variable; the predicted source regions for the cases considered were similar only for some dates in 2004 and 2006. During the analysed period, we found both cases, in which the predictions of the SILAM model variants and those of the HYSPLIT model were similar, and cases, in which there were substantial differences. In general, for complicated atmospheric circulation patterns the model predictions can be drastically different, with a tendency of trajectory model to fail reproducing the key episode features.     

Mesoscale Transport of Corylus Pollen Grains in Winter Atmosphere

Measurements of atmospheric pollen concentration were made at different sites of the Po Valley, Italy, during the winter of 1978. The concentration was determined with volumetric samplers both near the ground and at different heights up to 500 m. Only Corylus and Alnus pollen grains were found during the experimental period. Due to the large quantity of grains released and the detailed information available about the source areas, the Corylus pollen was used to investigate the features of atmospheric transport. It was found that the three-dimensional patterns of pollen concentration are strongly influenced by meteorological conditions. Moreover, it appears that pollen is present in the atmosphere for a longer time with respect to the emission period, due to the relevant effect of the resuspension of the deposited pollen grains. This effect is detectable at all the sampling points, and not only near the sources.     

野菊与菊花杂交中花粉活力和柱头可授性及胚胎发育研究

应用石蜡制片、活体压片、光学显微镜及扫描电子显微镜观察等方法,研究了四倍体河南云台山野菊(Dendranthema indicum)与栽培菊花'钟山金山'(D.grandiflorum 'Zhongshanjinshan')种间杂交中父本花粉活力、花粉在柱头萌发、花粉管生长及胚胎发育情况等.结果发现,父本云台山野菊的花粉活力在授粉时为12%左右.人工授粉后的不同时间,在柱头上都观察到正常萌发的花粉粒,且花粉管都能进入柱头,其中,在授粉后0.5 h时,平均每柱头有5.9粒花粉萌发;12 h时,为59.9粒;而24和48 h时,则分别降为47.1和35.7粒.此外,在授粉后8、10、12和15 d时,分别在49.1%、40.8%、39.7%和38.5%子房内观察到正常发育的胚胎,最终杂交结实率为44.8%,而母本自然开放结实率为52.3%.研究表明,授粉前其多数母本雌蕊发育良好、授粉后多数花粉能在柱头正常萌发和花粉管正常生长,在受精后大部分胚胎发育正常是野菊与栽培菊种间杂交较高结实率的重要保证,而授粉前父本较低的花粉活力对杂交结实率影响不大.     

Pollen size in Carex: The effect of different chemical treatments and mounting media

Pollen size and pollen aperture size for ten species of the genus Carex L., native to Estonia, have been measured using light microscopy. The species selected represent different sections of the genus, a range of habitats and different chromosome numbers. The effects of two basic chemical treatments, two mounting media and the effect of chemically induced dehydration with tertiary butyl alcohol (TBA) on the size of pollen grains were then recorded.

In general pollen size and pollen aperture size of the species examined is highly variable at both intraspecific and interspecific levels. Carex hirta has notably larger pollen grains than any of the other species investigated and, although correlations between size and chromosome number in the species examined are limited, it also has the highest chromosome number. Statistically significant size differences resulted from variations in chemical treatment, mounting media and tertiary butyl alcohol (TBA) induced dehydration. Acetolysed pollen grains are larger than potassium hydroxide (KOH) treated pollen grains. Pollen grains dehydrated after chemical treatment with TBA are larger than pollen grains not dehydrated. Pollen grains mounted in silicon oil are smaller than grains mounted in glycerine. But considering the great size variation of Carex pollen grains, the size changes caused by preparation procedures fall within the size variation range of the species examined.

All the samples contained a high number of deformed pollen grains and pollen grains with hardly distinguishable or no lateral apertures.     

The role of clothing fabrics as passive pollen collectors in the north‐eastern United States

The purpose of this investigation is to determine if clothing fabrics act as passive pollen collectors, and to determine if different fabrics vary with regard to the abundance and type of pollen trapped. Five of the most common fabrics in the United States (cotton, wool, polyester, silk and linen) were used to trap pollen. The pollen collecting apparatus was constructed of a 30?cm diameter circular needlepoint hoop, which vertically rotated freely, and was mounted on a dowel that was driven into the soil to chest height. Five pollen collectors, each with one of the five fabrics were placed at a collection site in rural, suburban, and urban habitats in Rhode Island for a 24?h period at weekly or biweekly intervals throughout 2002–2003. Pollen was washed from each of the fabrics and acetolysed. Total pollen per cm² removed from each of the fabric types was estimated using a haemocytometer. The pollen types were identified, and 200 grains were counted to determine the relative abundance of the various pollen types recovered from the fabrics. Clothing fabrics act as passive pollen collectors and the flora recovered from the fabric represent the qualitative and quantitative components of the pollen rain for that specific day. There are quantitative differences among the relative abundance of pollen types from the three habitats (urban, suburban, and rural). Washing with water and a detergent eliminates a majority of the pollen from the fabrics.     

An atmospheric pollen survey conducted during the winter in Minneapolis,Minnesota, USA

Few atmospheric pollen surveys have been conducted during the winter months in cities located in the midlatitudes. The purpose of this present investigation was to study pollen conditions during the winter in Minneapolis, Minnesota, a city that experiences cold temperatures and develops substantial snow cover. One hundred thirty‐three atmospheric samples were collected with a Rotorod Sampler between 11 October 1995 and 1 May 1996. Pollen was recovered in 109 samples, including 27 of the 40 samples collected in December and January. Twenty‐five types of pollen were observed during the study period; Cupressaceae (cedar/juniper), Ambrosia (ragweed) and Artemisia (sage/sagebrush) grains were most abundant during the period when local plants were not flowering. The weed pollen was most likely contributed by local sources, perhaps by dried flowers on dead plants. In contrast, the Cupressaceae pollen recovered in October and the early winter months is thought to have originated in the southern United States where several species of Juniperus flower late in the year. This study demonstrated that low but measurable concentrations of pollen occurred in the atmosphere throughout the winter.     

Wind Conditions and Pollen Deposition in a Mixed Deciduous Forest

Pollen deposition in a mixed deciduous forest in South Jutland, Denmark, was studied by means of pollen analyses (Andersen, 1970) and pollen collectors. In this connection it was important to know the wind conditions outside and inside the forest. Wind velocities and wind directions in the flowering seasons were measured at 2 stations in a 3-year period. High wind velocities prevail above the forest in spring and summer. At such wind velocities the difference in loss of large and small pollen grains by filtration in the tree tops is reduced. The winds inside the forest tend to turn into the direction of easiest flow. The velocities are about 20% of the outside wind before and 12–15% after the leafing. Single pollen grains released from the trees will be carried wide distances before deposition in the spring, and it is suggested that the tree pollen falls to the ground rather in aggregates or included in rain-drops.     

Pollen clumping and wind dispersal in an invasive angiosperm

Pollen dispersal is a fundamental aspect of plant reproductive biology that maintains connectivity between spatially separated populations. Pollen clumping, a characteristic feature of insect-pollinated plants, is generally assumed to be a detriment to wind pollination because clumps disperse shorter distances than do solitary pollen grains. Yet pollen clumps have been observed in dispersion studies of some widely distributed wind-pollinated species. We used Ambrosia artemisiifolia (common ragweed; Asteraceae), a successful invasive angiosperm, to investigate the effect of clumping on wind dispersal of pollen under natural conditions in a large field. Results of simultaneous measurements of clump size both in pollen shedding from male flowers and airborne pollen being dispersed in the atmosphere are combined with a transport model to show that rather than being detrimental, clumps may actually be advantageous for wind pollination. Initial clumps can pollinate the parent population, while smaller clumps that arise from breakup of larger clumps can cross-pollinate distant populations.     

Zum einfluß von niederschlägen auf pollen in der atmosphäre

Pollenkonzentrationsmessungen wurden mit handelsüblichen volumetrischen Pollenfallen in 1,8 und 18 m über Grund an demselben Standort durchgeführt. Das Ziel der Messungen lag in der Untersuchung der möglichen Beeinflussung des Pollenfluges während verschiedener Niederschlagsereignisse.

Die Pollenfallen waren auf dem Meßfeld des Wetteramtes Essen (Deutscher Wetterdienst) aufgestellt. Die Messung des Pollenfluges erfolgte in stündlichen Abständen in den Saisons von 1988 und 1989. Die Daten wurden mit den Ergebnissen eines Regenschreibers an demselben Standort korreliert. Daneben wurden 1988 bei ausgewählten Regenereignissen Regenproben aufgefangen und ihr Pollengehalt untersucht.

Mit beginnendem Niederschlagsbeginn konnte häufig ein schlagartiger Anstieg der Pollenregistrierung der Fallen in Bodennähe festgestellt werden. Analysen von Regentropfen in demselben Zeitraum zeigten dagegen nur einen geringen Pollengehalt. Die Erklärung für diesen Effekt liegt in vertikalen Luftströmungen, die bei Regenbeginn die Pollenkörner turbulent zwischen den Regentropfen aus höheren Luftschichten zur Erde herunterdrücken. Das turbulente Herabdrücken während des Regenschauers ist auch nach Ferntransport möglich.

Weiterhin ist ein Anstieg von Pollenkonzentration in Bodennähe durch die Wirkung von Regentropfen möglich, die die Blüten direkt treffen und damit Pollen aus den Stamina heraussschlagen.

Aus diesen Beobachtungen ist zu folgern, daß sich ein Pollenallergiker während eines Niederschlagsbeginns in einem geschlossenen Raum aufhalten sollte, da aus dem Regenbeginn eine Akkumulation von Pollen in Bodennähe resultieren kann.

Pollen data from two volumetric samplers, located at heights of 1,8 and 18 m above the ground, were used to investigate the influence of rainfall on pollen incidence. The counts were made by means of hourly analysis of the pollen concentration in the pollen season 1988 and 1989. These data were correlated with the data of a rain gauge. The traps were located in Essen in the lower Rhine area at the measurement field of the regional weather bureau of the German Weather Service. Rain samples were analysed for their pollen concentration at the same place in 1988. Besides this rain droplets were analyzed for the pollen content.

With the begin of rainfall the pollen concentration can increase explosively near the ground layer. Rain samples do not contain pollen whereas pollen traps indicate a high air concentration of pollen. The explanation for this effect is seen in air currents which force airborne pollen between the rain droplets turbulent down to the earth after they were dispersed by air convection in higher levels. The turbulent transport of pollen down to the ground can also be observed after long distance transport with rain.

A second observed effect of the begin of rainfall which can explosivly increase the pollen concentration near the ground is the pollen emission caused by the hit of the rain droplets on to the stamina of flowers, which are ready for pollen emission. This effect was only observed with the ground trap, whereas the high level trap did not register similar pollen concentrations.

As a result pollinosis patients are affected by these two impacts and should avoid to go outdoor in beginning rainfall and should close their windows immediately.     

POLLEN MORPHOLOGY AND PLANT TAXONOMY OF WHITE OAKS IN EASTERN NORTH AMERICA

An evaluation of possible approaches to fossil oak pollen identification utilized scanning electron microscopy to examine exine-surface features of 171 collections, representing 16 Quercus subgenus Lepidobalanus species and varieties of eastern North America. Twenty qualitative pollen morphological characters were defined and tabulated for each of 217 pollen grains. The data were subjected to cluster analysis and cluster diagrams were compared with published white oak taxonomy. Pollen morphology and plant taxonomy compared well in series of the subgenus Lepidobalanus due primarily to consistency of character presence and absence within species and varieties. Pollen morphology of white oaks appears to reflect plant systematics above the species level. Use of routine SEM analysis to identify series of white oaks among fossil pollen grains likely will yield valid results.     

Proteomic analyses of apoplastic proteins from germinating Arabidopsis thaliana pollen

Pollen grains play important roles in the reproductive processes of flowering plants. The roles of apoplastic proteins in pollen germination and in pollen tube growth are comparatively less well understood. To investigate the functions of apoplastic proteins in pollen germination, the global apoplastic proteins of mature and germinated Arabidopsis thaliana pollen grains were prepared for differential analyses by using 2-dimensional fluorescence difference gel electrophoresis (2-D DIGE) saturation labeling techniques. One hundred and three proteins differentially expressed (p value≤0.01) in pollen germinated for 6h compared with un-germination mature pollen, and 98 spots, which represented 71 proteins, were identified by LC-MS/MS. By bioinformatics analysis, 50 proteins were identified as secreted proteins. These proteins were mainly involved in cell wall modification and remodeling, protein metabolism and signal transduction. Three of the differentially expressed proteins were randomly selected to determine their subcellular localizations by transiently expressing YFP fusion proteins. The results of subcellular localization were identical with the bioinformatics prediction. Based on these data, we proposed a model for apoplastic proteins functioning in pollen germination and pollen tube growth. These results will lead to a better understanding of the mechanisms of pollen germination and pollen tube growth.     

Directional Guidance of Nicotiana alata Pollen Tubes in Vitro and on the Stigma

Pollen tubes navigate the route from stigma to ovule with great accuracy, but the cues that guide them along this route are not known. We reproduced the environment on the stigma of Nicotiana alata by immersing pollen in stigma exudate or oil close to an interface with an aqueous medium. The growth of pollen in this culture system mimicked growth on stigmas: pollen grains hydrated and germinated, and pollen tubes grew toward the aqueous medium. The rate-limiting step in pollen germination was the movement of water through the surrounding exudate or oil. By elimination of other potential guidance cues, we conclude that the directional supply of water probably determined the axis of polarity of pollen tubes and resulted in growth toward the interface. We propose that a gradient of water in exudate is a guidance cue for pollen tubes on the stigma and that the composition of the exudate must be such that it is permeable enough for pollen hydration to occur but not so permeable that the supply of water becomes nondirectional. Pollen tube penetration of the stigma may be the most frequently occurring hydrotropic response of higher plants.