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At least 811 records · Page 45Linked to original sources
PubMed1999

Comparing pollen and spore counts collected with the Rotorod Sampler and Burkard spore trap.

BACKGROUND: The Rotorod Sampler and Burkard spore trap are air-sampling instruments commonly used by allergists in the United States. Although both devices are volumetric, their principles of operation and particle recoveries differ. OBJECTIVE: This review will develop some guidelines for interpreting and comparing pollen counts obtained with these instruments. DATA SOURCES: Investigations examining particle recovery by each device will be reviewed. Five studies where the Rotorod and Burkard were operated in parallel will also be assessed. RESULTS: The Rotorod's theoretical and empirical collection efficiencies are low for particles <10 microm but typically exceed 80% for particles above this threshold. This instrument has traditionally been considered insensitive to wind; experimental data present a mixed picture. The Burkard offers high collection efficiencies, particularly for small particles, when an aerosol's velocity is low. Bi-directional errors in collection efficiency occur as a function of increasing wind speed and particle size. Parallel trapping investigations demonstrated that the Burkard yielded a higher estimate of the atmospheric particle concentration for all particle sizes. Differences were widest for small fungus spores but narrowed for pollen-sized particles. Some recovery differences are readily explained by sampling theory. Other disparities may reflect over-sampling, under-sampling or each device's principles of operation. CONCLUSIONS: Both instruments appear to record the same relative changes in airborne particle concentrations. The Burkard appears to be a superior instrument for sampling particles <10 microm. The Rotorod appears to be equal or superior to the Burkard for collecting particles >10 microm. A rough empirical means for comparing differences in particle recovery is presented.

Air Pollution↗
PubMed2001

Polarized cell growth in higher plants.

Pollen tubes and root hairs are highly elongated, cylindrically shaped cells whose polarized growth permits them to explore the environment for the benefit of the entire plant. Root hairs create an enormous surface area for the uptake of water and nutrients, whereas pollen tubes deliver the sperm cells to the ovule for fertilization. These cells grow exclusively at the apex and at prodigious rates (in excess of 200 nm/s for pollen tubes). Underlying this rapid growth are polarized ion gradients and fluxes, turnover of cytoskeletal elements (actin microfilaments), and exocytosis and endocytosis of membrane vesicles. Intracellular gradients of calcium and protons are spatially localized at the growing apex; inward fluxes of these ions are apically directed. These gradients and fluxes oscillate with the same frequency as the oscillations in growth rate but not with the same phase. Actin microfilaments, which together with myosin generate reverse fountain streaming, undergo rapid turnover in the apical domain, possibly being regulated by key actin-binding proteins, e.g., profilin, villin, and ADF/cofilin, in concert with the ion gradients. Exocytosis of vesicles at the apex, also dependent on the ion gradients, provides precursor material for the continuously expanding cell wall of the growing cell. Elucidation of the interactions and of the dynamics of these different components is providing unique insight into the mechanisms of polarized growth.

Actin Cytoskeleton↗
PubMed2002

Developmental and tissue-specific expression of CaMV 35S promoter in cotton as revealed by GFP.

The CaMV 35S promoter is the most commonly used promoter for driving transgene expression in plants. Though it is presumed to be a constitutive promoter, some reports suggest that it is not expressed in all cell types. In addition, the information available on its expression profile in all possible cell and tissue types and during early stages of development is incomplete. We present here a detailed expression profile of this promoter investigated using the green fluorescent protein (GFP) gene as a reporter system in cotton during embryo development, and in all the vegetative and floral cell and tissue types. GFP expression was not detected during the early stages of embryogenesis. The first perceptible GFP expression was observed in a small area at the junction of hypocotyl and cotyledons in embryos at around 13 days after anthesis. The GFP fluorescence progressively became stronger and expanded throughout the cotyledon and hypocotyl as embryo development advanced. After germination, varying levels of promoter activity were observed in all cell and tissue types in the hypocotyl, cotyledon, stem, leaf, petiole, and root. The promoter was also expressed in all floral parts. Although cotton pollen exhibited a low level of greenish autofluorescence, it was possible to discern GFP-dependent fluorescence in some of the pollen from all the T0 plants examined. Developing cotton fibers also exhibited GFP fluorescence suggesting that the 35S promoter was active in these specialized epidermal cells. Thus, we show that the expression of the 35S promoter was developmentally regulated during embryogenesis and that beyond a certain stage during embryogenesis, the promoter was expressed in most cell and tissue types in cotton albeit at different levels.

Caulimovirus↗
PubMed1996

New in situ approaches to study the induction of pollen embryogenesis in Capsicum annuum L.

The induction of pollen embryogenesis in Capsicum annuum L. has been studied at the cellular level using various in situ approaches with several molecular probes for DNA, RNA and proteins. The late vacuolated microspore and the young bicellular pollen grain are stages of gametophytic development in which embryogenesis can be induced. Our results show that the late vacuolated microspore stage is most responsive to embryogenesis induction. The proliferating cell nuclear antigen (PCNA) has been immunolocalized at the electron microscopy level, in order to map replication sites in relation to the fine structure of chromatin. It shows different patterns of labelling at both developmental stages studied, revealing that the late vacuolated microspore is in a period of replication. Other in situ studies have been performed to characterize the state of nuclear activity at the specific developmental stages in which the embryogenic induction can occur. The modern in situ terminal-deoxy-nucleotidyl transferase (TdT) reaction for DNA, the immunolocalization of various nuclear antigens (as snRNPs, fibrillarin, RNA) and the ultrastructural in situ hybridization using 18S and 25S ribosomal probes provided valuable data bout the specific features displayed by the functional nuclear compartments of the microspore, and the young vegetative and generative cells. They are related not only to the state of gene activity but also with probably the ability to switch to the sporophytic pathway at specific developmental times of their gametophytic program.

Capsicum↗
PubMed2001

Two-generation analysis of pollen flow across a landscape. III. Impact of adult population structure.

The rate and distance of instantaneous pollen flow in a population are parameters of considerable current interest for plant population geneticists and conservation biologists. We have recently developed an estimator (phi ft) of differentiation between the inferred pollen clouds that fertilize several females, sampled within a single population. We have shown that there is a simple relation between phi ft and the average pollen dispersal distance (delta) for the case of a population with no geographic structure. Though forest trees usually show considerable pollen flow, assuming an absence of spatially distributed genetic structure is not always wise. Here, we develop analytical theory for the relation between phi ft and delta, for the case where the probability of Identity by Descent (IBD) for two individuals decreases with the physical distance between them. This analytical theory allows us to provide an effective method for estimating pollen dispersal distance in a population with adult genetic structure. Using real examples, we show that estimation errors can be large if genetic structure is not taken into account, so it is wise to evaluate adult genetic structure simultaneously with estimation of phi ft for the pollen clouds. We show that the results are only moderately affected by changes in the decay function, a result of some importance since no completely established theory is available for this function.

Genetics, Population↗
PubMed2002

Development and function of the angiosperm female gametophyte.

The plant life cycle alternates between a diploid sporophyte generation and a haploid gametophyte generation. The angiosperm female gametophyte is critical to the reproductive process. It is the structure within which egg cell production and fertilization take place. In addition, the female gametophyte plays a role in pollen tube guidance, the induction of seed development, and the maternal control of seed development. Genetic analysis in Arabidopsis has uncovered mutations that affect female gametophyte development and function. Mutants defective in almost all stages of development have been identified, and analysis of these mutants is beginning to reveal features of the female gametophyte developmental program. Other mutations that affect female gametophyte function have uncovered regulatory genes required for the induction of endosperm development. From these studies, we are beginning to understand the regulatory networks involved in female gametophyte development and function. Further investigation of the female gametophyte will require complementary approaches including expression-based approaches to obtain a complete profile of the genes functioning within this critical structure.

Arabidopsis↗
PubMed2005

Arabidopsis vacuolar H-ATPase subunit E isoform 1 is required for Golgi organization and vacuole function in embryogenesis.

Vacuolar H(+)-ATPases play an important role in maintaining the pH of endomembrane compartments in eukaryotic cells. The functional relevance of this homeostasis for multicellular development has not been studied in plants. Here, we analyze the biological consequences resulting from the lack of subunit E isoform 1 (VHA-E1) encoded by the Arabidopsis TUFF gene. tuff mutant embryos are lethal, displaying variably enlarged cells with multiple nuclei, large vacuoles containing inclusions, abnormal organization of Golgi stacks, and cell wall defects. Rescue of embryo lethality by cell cycle-regulated expression of VHA-E1 results in abnormal seedlings with non-functional meristems and defective cell differentiation. VHA-E1 is the predominant isoform in embryogenesis whereas VHA-E3 is expressed mainly in the endosperm and surrounding maternal tissues during seed development, and VHA-E2 is pollen-specific. VHA-E1 protein accumulates at endomembrane compartments including vacuoles and endosomes, but appears absent from the plasma membrane. Our results suggest an essential role for VHA-E1 in maintaining a functional secretory system during somatic development but not in the haploid gametophytes.

Amino Acid Sequence↗
PubMed1992

Monoclonal antibodies against Olea europaea major allergen: allergenic activity of affinity-purified allergen and depleted extract and development of a radioimmunoassay for the quantitation of the allergen.

Several monoclonal antibodies (MAbs) were raised against Olea europaea pollen-extract components. Two of these antibodies, named OL 2 and OL 7, recognize two nonoverlapping, nonrepeating epitopes on the olive-allergen Ole e I, as demonstrated by different techniques. The allergen was purified in a single step by MAb-based affinity chromatography, and the allergen revealed a band at molecular weight 20 kd as well as a minor band at 18 kd on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The contribution of allergen Ole e I to the allergenic activity of O. europaea pollen extracts was determined from the effect of allergen depletion by affinity chromatography on skin reactivity and a histamine-release test. The removal of allergen caused a large reduction in the activity of the preparation in 25 monospecific olive-allergic patients. In agreement, the affinity-purified allergen demonstrated a similar response when it was compared with the whole extract in these assays. The results indicated that Ole e I is by far the most important olive-pollen allergen. A two-site solid-phase radioimmunoassay was developed for the quantitation of the allergen Ole e I in mass units. The assay was based on the MAbs, OL 2 and OL 7, and had a detection limit in the nanogram range. A good correlation was found between allergenic activity, as determined by RAST inhibition, and allergen content in 18 olive-pollen extracts. This result indicates that the assay can be a good alternative to RAST inhibition for the standardization of O. europaea extracts.

Allergens↗
PubMed2004

Inhibition of plant protein synthesis by the cyanobacterial hepatotoxin, cylindrospermopsin.

Cylindrospermopsin, a cyanobacterial guanidine alkaloid hepatotoxin and protein synthesis-inhibitor, was assayed for its effects on the germination of pollen from tobacco (Nicotiana tabacum cv Samsun NN). Pollen germination, measured by Alcian Blue dye-binding, was inhibited by cylindrospermopsin between 5 and 1000 microg ml(-1). As a protein synthesis-inhibitor, cylindrospermopsin did not inhibit pollen germination to the same extent as cycloheximide on a gravimetric basis, but significantly reduced the amount of (14)C-(U)-l-leucine labelling in pollen tubes. The inhibition of tobacco pollen germination may be amenable for development as a bioassay for cylindrospermopsin, although this would require a pre-concentration step for the monitoring of environmental samples. Implications of these observations for current spray-irrigation practices are discussed.

Alcian Blue↗
PubMed2000

Analysis of the spaceflight effects on growth and development of Super Dwarf wheat grown on the Space Station Mir.

The hypothesis being tested is that Super Dwarf wheat, Triticum aestivum L., plants in the Svet Greenhouse onboard the Russian Space Station Mir will complete a life cycle in spaceflight, providing that the environmental conditions necessary for adequate growth on Earth are supplied. Twenty six seeds of wheat were planted in each of 2 rows of 2 root compartments for a total of 104 seeds in Svet. Germination rate at 7 d was 56 and 73% on Mir and 75 and 90% in ground-based controls. Plants were grown throughout the whole cycle of ontogenesis (123 d) with samples gathered at different times to validate the morphological and reproductive stages of the plants. Young plants showed vigorous early seedling growth, with large biomass production, including the formation of 280 floral spikes. Upon return to Earth, comparative analyses showed that the number of tillers and flowers per spikelet were 63.2% and 40% greater, respectively, in Mir-grown plants than in the controls. By contrast, the stem length (52.4%), spike mass (49.2%) and length (23.1%), awn length (75.7%), number of spikelets per spike (42.8%) and number of seeds per spike (100% sterile) from Mir-grown plants were substantially less than the controls. Distribution of moisture and roots throughout the substrate was very good. All florets on Mir-grown spikes ceased development at the same stage of ontogeny. Lack of caryopses formation was attributed to male sterility occurring at different stages of staminal development. Anthers failed to dehisce and pollen grains were smaller and shriveled compared to the controls, suggesting a chronic stress had occurred in the Svet growth chamber. Recent ground-based studies indicated that ethylene, which was measured at 0.3 to 1.8 mg kg-1 in the Mir, almost certainly could have induced male sterility in the wheat plants grown on the Mir.

Atmosphere↗
PubMed1984

Military antishock trousers in a patient with adrenergic-resistant anaphylaxis.

The case presented concerns a patient taking propranolol who developed a severe anaphylactic reaction to pollen extract immunotherapy. Although the hypotension that occurred during the anaphylaxis was refractory to intravenous fluids, epinephrine, and dopamine, the antishock trouser suit was effective in elevating blood pressure.

Adult↗
PubMed2003

Reproductive biology of Butea monosperma (Fabaceae).

The reproductive biology encompassing phenology, floral biology, pollination and breeding systems, of Butea monosperma, a beautiful tree of the Indian subcontinent, was investigated in a protected dry, deciduous forest located in New Delhi. Phenological studies indicated that although the species shows a regular flowering season, all trees do not flower every year. Flowers are typically papilionaceous; the stigma is wet papillate and the style is hollow. The flowers show characteristics of bird pollination being large and bright orange-red in colour with copious amounts of nectar, and exhibiting diurnal anthesis. Although the flowers are frequented by as many as seven species of birds belonging to six families, only one species, the purple sunbird (Nectarinia asiatica), is the effective pollinator. The flowers are also pollinated by the three-striped squirrel (Funambulus tristiatus). Unlike other flower visitors, these two pollinators forage the nectar from the open side of the keel (legitimate path) during which pollen grains are deposited on their body parts. After the first visit of a sunbird or a squirrel, virgin flowers showed pollen load on the stigma and developed into fruits. B. monosperma shows a weak form of self-incompatibility. Fruit set following manual self-pollination (5.25 %) was comparable with open-pollination (approx. 5 %) but was significantly lower than manual cross-pollination (22.51 %). This indicates that there is a high degree of geitonogamous pollination in this species, which may lead to a weakening of self-incompatibility as a means of reproductive assurance. The results are analysed in the light of prevailing discussions on specialized vs. generalized pollination systems.

Butea↗
PubMedDate not supplied

Programmed cell death and hybrid incompatibility.

We propose a new theory to explain developmental aberrations in plant hybrids. In our theory, hybrid incompatibilities arise from imbalances in the mechanisms that cause male sterility in hermaphroditic plants. Mitochondria often cause male sterility by killing the tapetal tissue that nurtures pollen mother cells. Recent evidence suggests that mitochondria destroy the tapetum by triggering standard pathways of programmed cell death. Some nuclear genotypes repress mitochondrial male sterility and restore pollen fertility. Normal regulation of tapetal development therefore arises from a delicate balance between the disruptive effects of mitochondria and the defensive countermeasures of the nuclear genes. In hybrids, incompatibilities between male-sterile mitochondria and nuclear restorers may frequently upset the regulatory control of programmed cell death, causing tapetal abnormalities and male sterility. We propose that hybrid misregulation of programmed cell death may also spill over into other tissues, explaining various developmental aberrations observed in hybrids.

Apoptosis↗
PubMed2004

Cytogenetics of semi-fertile triploid and aneuploid intergeneric vine cacti hybrids.

Crosses between the diploid Hylocereus polyrhizus, as the female parent, and the tetraploid Selenicereus megalanthus, as the male parent, yielded triploid and aneuploid hybrids. The fruits of these hybrids combined the attractive appearance of Hylocereus fruits with the delicious taste of S. megalanthus fruits. The aim of this work was to assess the fertility and breeding potential of the triploid and aneuploid hybrids with a view to developing an improved vine cactus crop. Pollen mother cells at metaphase I revealed univalents, bivalents, trivalents, and occasionally quadrivalents. Chromosome distribution at anaphase I revealed different classes of chromosome segregation as well as lagging chromosomes. At metaphase II, parallel and tripolar spindles were observed. The occurrence of triads was frequent, whereas dyads were rarely observed. Pollen stainability varied among the clones studied ranging from 9.8% to 18.6%. The diameters of the stained pollen grains varied widely, probably as a result of the number of chromosomes. Despite the allotriploid origin of our hybrids, functional female and male gametes were produced in considerable proportions, most likely as a result of balanced chromosome segregation. The triploid and aneuploid clones studied yielded viable seeds whose number per fruit was strongly dependent on the pollen donor.

Breeding↗
PubMed1998

Family of MADS-Box genes expressed early in male and female reproductive structures of monterey pine

Three MADS-box genes isolated from Monterey pine (Pinus radiata), PrMADS1, PrMADS2, and PrMADS3, are orthologs to members of the AGL2 and AGL6 gene subfamilies in Arabidopsis. These genes were expressed during early stages of pine shoot development in differentiating seed- and pollen-cone buds. Their transcripts were found within a group of cells that formed ovuliferous scale and microsporophyll primordia. Expression of PrMADS3 was also detected in a group of cells giving rise to needle primordia within differentiated vegetative buds, and in needle primordia.

Journal Article↗
PubMed2000

Tissue-specific and developmental pattern of expression of the rice sps1 gene.

Sucrose-phosphate synthase (SPS) is one of the key regulatory enzymes in carbon assimilation and partitioning in plants. SPS plays a central role in the production of sucrose in photosynthetic cells and in the conversion of starch or fatty acids into sucrose in germinating seeds. To explore the mechanisms that regulate the tissue-specific and developmental distribution of SPS, the expression pattern of rice (Oryza sativa) sps1 (GenBank accession no. U33175) was examined by in situ reverse transcriptase-polymerase chain reaction and the expression directed by the sps1 promoter using the beta-glucuronidase reporter gene. It was found that the expression of the rice sps1 gene is limited to mesophyll cells in leaves, the scutellum of germinating seedlings, and pollen of immature inflorescences. During leaf development, the sps1 promoter directs a basipetal pattern of expression that coincides with the distribution of SPS activity during the leaf sink-to-source transition. It was also found that during the vegetative part of the growth cycle, SPS expression and enzymatic activity are highest in the youngest fully expanded leaf. Additionally, it was observed that the expression of the sps1 promoter is regulated by light and dependent on plastid development in photosynthetic tissues, whereas expression in scutellum is independent of both light and plastid development.

Base Sequence↗
PubMed2004

Phleum pratense pollen starch granules induce humoral and cell-mediated immune responses in a rat model of allergy.

BACKGROUND: Timothy grass (Phleum pratense) pollen allergens are an important cause of allergic symptoms. However, pollen grains are too large to penetrate the deeper airways. Grass pollen is known to release allergen-bearing starch granules (SG) upon contact with water. These granules can create an inhalable allergenic aerosol capable of triggering an early asthmatic response and are implicated in thunderstorm-associated asthma. OBJECTIVE: We studied the humoral (IgE) and bronchial lymph node cells reactivities to SG from timothy grass pollen in pollen-sensitized rats. METHODS: Brown-Norway rats were sensitized (day 0) and challenged (day 21) intratracheally with intact pollen and kept immunized by pollen intranasal instillation by 4 weeks intervals during 3 months. Blood and bronchial lymph nodes were collected 7 days after the last intranasal challenge. SG were purified from fresh timothy grass pollen using 5 microm mesh filters. To determine the humoral response (IgE) to SG, we developed an original ELISA inhibition test, based on competition between pollen allergens and purified SG. The cell-mediated response to SG in the bronchial lymph node cells was determined by measuring the uptake of [3H]thymidine in a proliferation assay. RESULTS: An antibody response to SG was induced, and purified SG were able to inhibit the IgE ELISA absorbance by 45%. Pollen extract and intact pollen gave inhibitions of 55% and 52%, respectively. A cell-mediated response was also found, as pollen extract, intact pollen and SG triggered proliferation of bronchial lymph node cells. CONCLUSIONS: It was confirmed that timothy grass pollen contains allergen-loaded SG, which are released upon contact with water. These granules were shown to be recognized by pollen-sensitized rats sera and to trigger lymph node cell proliferation in these rats. These data provide new arguments supporting the implication of grass pollen SG in allergic asthma.

Allergens↗