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At least 433 records · Page 24Linked to original sources
PubMed2003

Time series analysis demonstrates the absence of pulsatile hyphal growth.

Hyphal tip growth has been previously reported as pulsatile, defined as regularly alternating fast and slow rates of extension. The growth of pollen tubes, and hyphae of Neurospora crassa and Saprolegnia ferax were analysed using high spatial and temporal resolution. By using long (100-500 s) records of growth rate, sampled every second, it was possible to apply rigorous statistical analysis of the time series. As previously demonstrated, pollen tubes can show pulsatile growth, detectable with this system. In contrast, hyphal growth rates do not show any evidence of pulsatile growth; instead, growth rates appear to fluctuate randomly. It is concluded that pulsatile growth is not a common feature of hyphal tip growth.

Fourier Analysis↗
PubMed2006

Roles of the ubiquitin/proteasome pathway in pollen tube growth with emphasis on MG132-induced alterations in ultrastructure, cytoskeleton, and cell wall components.

The ubiquitin/proteasome pathway represents one of the most important proteolytic systems in eukaryotes and has been proposed as being involved in pollen tube growth, but the mechanism of this involvement is still unclear. Here, we report that proteasome inhibitors MG132 and epoxomicin significantly prevented Picea wilsonii pollen tube development and markedly altered tube morphology in a dose- and time-dependent manner, while hardly similar effects were detected when cysteine-protease inhibitor E-64 was used. Fluorogenic kinetic assays using fluorogenic substrate sLLVY-AMC confirmed MG132-induced inhibition of proteasome activity. The inhibitor-induced accumulation of ubiquitinated proteins (UbPs) was also observed using immunoblotting. Transmission electron microscopy revealed that MG132 induces endoplasmic reticulum (ER)-derived cytoplasmic vacuolization. Immunogold-labeling analysis demonstrated a significant accumulation of UbPs in degraded cytosol and dilated ER in MG132-treated pollen tubes. Fluorescence labeling with fluorescein isothiocyanate-phalloidin and beta-tubulin antibody revealed that MG132 disrupts the organization of F-actin and microtubules and consequently affects cytoplasmic streaming in pollen tubes. However, tip-focused Ca2+ gradient, albeit reduced, seemingly persists after MG132 treatment. Finally, fluorescence labeling with antipectin antibodies and calcofluor indicated that MG132 treatment induces a sharp decline in pectins and cellulose. This result was confirmed by Fourier transform infrared analysis, thus demonstrating for the first time the inhibitor-induced weakening of tube walls. Taken together, these findings suggest that MG132 treatment promotes the accumulation of UbPs in pollen tubes, which induces ER-derived cytoplasmic vacuolization and depolymerization of cytoskeleton and consequently strongly affects the deposition of cell wall components, providing a mechanistic framework for the functions of proteasome in the tip growth of pollen tubes.

Actin Cytoskeleton↗
PubMed2005

Similarity of vegetation dynamics during interglacial periods.

The Velay sequence (France) provides a unique, continuous, palynological record spanning the last four climatic cycles. A pollen-based reconstruction of temperature and precipitation displays marked climatic cycles. An analysis of the climate and vegetation changes during the interglacial periods reveals comparable features and identical major vegetation successions. Although Marine Isotope Stage (MIS) 11.3 and the Holocene had similar earth precessional variations, their correspondence in terms of vegetation dynamics is low. MIS 9.5, 7.5, and especially 5.5 display closer correlation to the Holocene than MIS 11.3. Ecological factors, such as the distribution and composition of glacial refugia or postglacial migration patterns, may explain these discrepancies. Comparison of ecosystem dynamics during the past five interglacials suggests that vegetation development in the current interglacial has no analogue from the past 500,000 years.

Climate↗
PubMed1975

Effect of dose rate and exposure time on the stimulation effect of tube growth of Pinus silvestris pollen.

The stimulating effect of ionizing radiation in respect to dose rate and exposure time was studied using the tube growth of Pinus silvestris pollen. Stimulation was registered with a small dose (50 rad) supplied at low dose rates (0.5; 1.0; 3.0 and 5.0 rad/sec) and with higher doses (300, 800 and 1400 rad) supplied at higher dose rates (10; 40 and 50 rad/sec). This suggests that only the exposure time is of importance for radiation-induced stimulation provided that the exposure time does not exceed 100 sec.

Dose-Response Relationship, Radiation↗
PubMed2003

Meteorologic variables in aerobiology.

Although prevalent weather helps define climate, individual weather conditions, such as rain, humidity, wind speed and direction, temperature, or amount of sunshine, may have direct and indirect effects on bioaerosols. Effects may be immediate or cumulative. Precipitation and humidity acutely decrease particle air burden, but sufficient preseason moisture is necessary to assure proper growth of flower buds on perennials and trees and growth of annuals in general. Ambient temperature increase is necessary for anthesis in many plants, and cumulative heat above a threshold value has been linked to onset and intensity of pollination in grasses, weeds, and trees. Wind direction only impacts if there is lack of uniformity in the pollen sources that surround sampling sites. Wind speed may factor in re-entrainment of settled particles or may act to scour the air. Thunderstorms provide a unique sum of factors that greatly may increase aeroallergen burden. Dispersal of mold spores is linked intimately to precipitation and humidity. The effects may be opposed diametrically, however, depending on the type of fungi. Certain ascospores and basidiospores require active rainfall for release of spores, whereas other Deuteromycetes are suppressed by precipitation.

Aerosols↗
PubMed2004

Impacts of climate change on aeroallergens: past and future.

Human activities are resulting in increases in atmospheric greenhouse gases, such as carbon dioxide, and changes in global climate. These, in turn, are likely to have had, and will continue to have, impacts on human health. While such impacts have received increasing attention in recent years, the impacts of climate change on aeroallergens and related allergic diseases have been somewhat neglected. Despite this, a number of studies have revealed potential impacts of climate change on aeroallergens that may have enormous clinical and public health significance. The purpose of this review is to synthesize this work and to outline a number of research challenges in this area. There is now considerable evidence to suggest that climate change will have, and has already had, impacts on aeroallergens. These include impacts on pollen amount, pollen allergenicity, pollen season, plant and pollen distribution, and other plant attributes. There is also some evidence of impacts on other aeroallergens, such as mould spores. There are many research challenges along the road to a more complete understanding of the impacts of climate change on aeroallergens and allergic diseases such as asthma and hayfever. It is important that public health authorities and allergy practitioners be aware of these changes in the environment, and that research scientists embrace the challenges that face further work in this area.

Air↗
PubMed2006

Differential display proteomic analysis of Picea meyeri pollen germination and pollen-tube growth after inhibition of actin polymerization by latrunculin B.

To investigate roles of the actin cytoskeleton in growth of the pollen tube of Picea meyeri, we used the actin polymerization inhibitor latrunculin B (LATB) under quantitatively controlled conditions. At low concentrations, LATB inhibited polymerization of the actin cytoskeleton in the growing pollen tube, which rapidly inhibited tip growth. The proteomic approach was used to analyse protein expression-profile changes during pollen germination and subsequent pollen-tube development with disturbed organization of the actin cytoskeleton. Two-dimensional electrophoresis and staining with Coomassie Brilliant Blue revealed nearly 600 protein spots. A total of 84 of these were differentially displayed at different hours with varying doses of LATB, and 53 upregulated or downregulated proteins were identified by mass spectrometry. These proteins were grouped into distinct functional categories including signalling, actin cytoskeleton organization, cell expansion and carbohydrate metabolism. Moreover, actin disruption affected the morphology of Golgi stacks, mitochondria and amyloplasts, along with a differential expression of proteins involved in their functions. These findings provide new insights into the multifaceted mechanism of actin cytoskeleton functions and its interaction with signalling, cell-expansion machinery and energy-providing pathways.

Actin Cytoskeleton↗
PubMed1997

Tip localized Ca2+ pulses are coincident with peak pulsatile growth rates in pollen tubes of Lilium longiflorum.

It is known that locally elevated Ca2+ at the growing tips of pollen tubes is necessary for pollen tube elongation. Here we show that this localized Ca2+ is also temporally regulated and is closely associated with pulsatile tip growth. Lilium longiflorum pollen tubes were injected with the photoprotein, aequorin, and the Ca2(+)-dependent light output was detected with a low noise photon-counting system. Ca2+ pulses with a mean period of 40 seconds were invariably associated with growth. The pulses were sporadic and of low amplitude for about the first 1.5 hours after germination. With subsequent growth, pulses increased in amplitude and the period between pulses became more regular. We have localized these Ca2+ pulses to the elongating end of the growing tube. The Ca2+ pulses are asymmetrical, rising more slowly than they fall. We estimate that the Ca2+ concentration at the peak of the pulses reaches nearly 10 microM. The addition of 100 microM La3+, a Ca2+ channel blocker, extinguished the pulses. An analysis of growth of elongating tubes establishes that extension is pulsatile, with a 42 second period between pulses. Calcium imaging, using the fluorescent indicator, Calcium Green dextran, shows that calcium pulses are coincident with peak growth rates.

Aequorin↗
PubMed2004

Development of a competitive ELISA for the evaluation of sunflower pollen in honey samples.

We report the development of a rapid, specific, and sensitive enzyme-linked immunoassay (ELISA) for the evaluation of sunflower pollen in honey as a method alternative to melissopalynology, which is considered the standard technique for the evaluation of floral origin of honey. Two 33-36 kDa proteins, identified as characteristic of sunflower pollen, were isolated and used as coating antigens in the competitive ELISA. We verified its analytical performance by evaluating reproducibility, specificity, and exactitude in relation to melissopalynology. The competitive ELISA developed during this work is able to quantify sunflower pollen in honey, with a detection limit of 10%, showing linear response between 10 and 90%. The method afforded low cross reactivity with honey from other floral origin, thus evidencing an adequate selectivity. We also observed a significant correlation (r = 0.975; p < 0.001) when the proposed ELISA was referenced to melissopalynology. Hence, we conclude that the competitive ELISA constitutes a valuable and feasible alternative for authentication of sunflower honey. This work opens the possibility to develop similar assays for other pollen types.

Binding, Competitive↗
PubMed1992

Roles for the extracellular matrix in plant development and pollination: a special case of cell movement in plants.

Pattern formation in plants is now thought to be primarily dependent on positional information during development. We discuss the prevalent theories on how position is deciphered by cells in an organism and highlight the recent advances implicating molecules of the cell wall or extracellular matrix (ECM) in this process. We compare the functions of the ECM in plants and animals and describe the various cell and substrate adhesion molecules of the animal ECM which play a role in morphogenesis and cell movement. We propose that analogous molecules may occur in plants and provide evidence for the presence of a substrate adhesion molecule like vitronectin in plants and algae. We provide a model for how substrate adhesion molecules may be involved in a special case of cell movement in plants, pollination.

Animals↗
PubMed1997

Olfactory dysfunction in allergic rhinitis is related to nasal eosinophilic inflammation.

BACKGROUND: Olfactory dysfunction is a common finding in patients suffering from allergic rhinitis. However, little is known about the pathophysiology underlying this phenomenon and about the time course of hyposmia in seasonal allergy. METHODS: A prospective controlled study was performed on 17 patients with allergic rhinitis to grass pollen in order to evaluate olfactory function in correlation to the duration of allergen exposition, symptoms, eosinophil cationic protein (ECP) in nasal secretions, and nasal volume flow (NVF). Olfactory function was evaluated preseasonally and on days 3, 7, 14, and 21 of the season using a modified Connecticut Chemosensory Clinical Research Center testing procedure for threshold, identification, and discrimination. Twelve volunteers without allergy served as controls. RESULTS: Preseasonally, patients and controls performed equally in discrimination and identification testing, but not in threshold testing. No changes were found in the controls, but a significant decrease in threshold and identification from the 7th day of the season in patients with allergy was noted that was better correlated to ECP than to NVF. NVF was already maximally decreased from the 3rd intraseasonal day with no further changes. ECP increase became significant at day 14. CONCLUSION: Patients with grass pollen allergy develop olfactory dysfunction during natural allergen exposure that might be related to allergic inflammatory mechanisms.

Adult↗
PubMed2000

Perturbation in linker histone content has no effect on the cell cycle but affects the cell size of suspension grown tobacco BY-2 cells.

Histone H1, a key structural element of eukaryotic chromosomes can be perturbed in plants in vivo by overexpression or by a change in the proportion of native H1 variants (Prymakowska-Bosak M., Przewloka M., Iwkiewicz J., Egierszdorff S., Kuras M., Chaubert N., Gigot C., Spiker S., Jerzmanowski A., Histone H1 overexpressed to high level in tobacco affects certain developmental programs but has limited effect on basal cellular functions, Proc. Natl. Acad. Sci. U.S.A. 93 (1996) 10250-10255; Prymakowska-Bosak M., Slusarczyk J., Przewloka M., Kuras M., Lichota J., Kilianczyk B., Jerzmanowski A., Linker Histones Play a Role in Male Meiosis and the Development of Pollen Grains in Tobacco, Plant Cell 11 (1999) 2317-2330). In order to analyze the possible causes of the specific phenotypic changes observed in whole plants we employed a simpler system of tobacco BY-2 cell line. We show that the BY-2 cells engineered to overexpress a major variant of Arabidopsis H1 or with the level of native major variants of H1 decreased by antisense strategy maintain the normal ability to grow and the normal length of the cell cycle. In the cells with perturbed H1 histones no change was observed in the organization of mitotic spindle or actin filaments of the cytoskeleton. The only visible phenotypic change occurred in cells overexpressing H1 that showed an increased frequency of cells with unusually large size. This phenotype was correlated with subtle but reproducible changes in the organization of cortical microtubules.

Journal Article↗
PubMed2000

Characterization of a ubiquitous expressed gene family encoding polygalacturonase in Arabidopsis thaliana.

Pectin, as one of the major components of plant cell wall, has been implicated in many developmental processes occurring during plant growth. Among the different enzymes known to participate in the pectin structure modifications, polygalacturonase (PG) activity has been shown to be associated with fruit ripening, organ abscission and pollen grain development. Until now, sequence analyses of the deduced polypeptides of the plant PG genes allowed their grouping into three clades corresponding to genes involved in one of these three activities. In this study, we report the sequence of three genomic clones encoding PG in Arabidopsis thaliana. These genes, together with 16 other genes present in the databases form a large gene family, ubiquitously expressed, present on the five chromosomes with at least two gene clusters on chromosomes II and V, respectively. Phylogenetic analyses suggest that the A. thaliana gene family contains five classes of genes, with three of them corresponding to the previously defined clades. Comparison of positions and numbers of introns among the A. thaliana genes reveals structural conservation between genes belonging to the same class. The pattern of intron losses that could have given rise to the PG gene family is consistent with a mechanism of intron loss by replacement of an ancestral intron-containing gene with a reverse-transcribed DNA copy of a spliced mRNA. Following this event of intron loss, the acquisition of introns in novel positions is consistent with a mechanism of intron gain at proto-splice sites.

Amino Acid Sequence↗
PubMed2003

Microarray and differential display identify genes involved in jasmonate-dependent anther development.

Jasmonate (JA) is a signaling compound essential for anther development and pollen fertility in Arabidopsis. Mutations that block the pathway of JA synthesis result into male sterility. To understand the processes of anther and pollen maturation, we used microarray and differential display approaches to compare gene expression pattern in anthers of wild-type Arabidopsis and the male-sterile mutant, opr3. Microarray experiment revealed 25 genes that were up-regulated more than 1.8-fold in wild-type anthers as compared to mutant anthers. Experiments based on differential display identified 13 additional genes up-regulated in wild-type anthers compared to opr3 for a total of 38 differentially expressed genes. Searches of the Arabidopsis and non-redundant databases disclosed known or likely functions for 28 of the 38 genes identified, while 10 genes encode proteins of unknown function. Northern blot analysis of eight representative clones as probes confirmed low expression in opr3 anthers compared with wild-type anthers. JA responsiveness of these same genes was also investigated by northern blot analysis of anther RNA isolated from wild-type and opr3 plants, In these experiments, four genes were induced in opr3 anthers within 0.5-1 h of JA treatment while the remaining genes were up-regulated only 1-8 h after JA application. None of these genes was induced by JA in anthers of the coil mutant that is deficient in JA responsiveness. The four early-induced genes in opr3 encode lipoxygenase, a putative bHLH transcription factor, epithiospecifier protein and an unknown protein. We propose that these and other early components may be involved in JA signaling and in the initiation of developmental processes. The four late genes encode an extensin-like protein, a peptide transporter and two unknown proteins, which may represent components required later in anther and pollen maturation. Transcript profiling has provided a successful approach to identify genes involved in anther and pollen maturation in Arabidopsis.

Acetates↗
PubMed2004

Diet-dependent effects of gut bacteria on their insect host: the symbiosis of Erwinia sp. and western flower thrips.

Studies on bacteria in the gut of insect species are numerous, but their focus is hardly ever on the impact on host performance. We showed earlier that Erwinia bacteria occur in the gut of western flower thrips, most probably acquired during feeding. Here, we investigate whether thrips gain a net benefit or pay a net cost because of these gut bacteria. On a diet of cucumber leaves, the time to maturity is shorter and the oviposition rate is higher in thrips with bacteria than in thrips without (aposymbionts). When fed on cucumber leaves and pollen, aposymbionts develop faster and lay more eggs. So Erwinia bacteria benefit or parasitize their thrips hosts depending on the diet, which is in accordance with theoretical predictions for fitness of organisms engaged in symbiotic interactions. Possibly, the transmission of gut bacteria has not become strictly vertical because of this diet-dependent fitness variability.

Analysis of Variance↗