13,020 research outputs found
An extracellular transglutaminase is required for apple pollen tube growth
No full textAn extracellular form of the calcium-dependent protein-crosslinking enzyme TGase (transglutaminase) was demonstrated to be involved in the apical growth of Malus domestica pollen tube. Apple pollen TGase and its substrates were co-localized within aggregates on the pollen tube surface, as determined by indirect immunofluorescence staining and the in situ cross-linking of fluorescently labelled substrates. TGase-specific inhibitors and an anti-TGase monoclonal antibody blocked pollen tube growth, whereas incorporation of a recombinant fluorescent mammalian TGase substrate (histidine-tagged green fluorescent protein:His6– Xpr–GFP) into the growing tube wall enhanced tube length and germination, consistent with a role of TGase as a modulator of cell wall building and strengthening. The secreted pollen TGase catalysed the cross-linking of both PAs (polyamines) into proteins (released by the pollen tube) and His6-Xpr-GFP into endogenous or exogenously added substrates. A similar distribution of TGase activitywas observed in planta on pollen tubes germinating inside the style, consistent with a possible additional role for TGase in the interaction between the pollen tube and the style during fertilization
Effective long-distance pollen dispersal in Centaurea jacea
No full textBACKGROUND: Agri-environment schemes play an increasingly important role for the conservation of rare plants in intensively managed agricultural landscapes. However, little is known about their effects on gene flow via pollen dispersal between populations of these species. METHODOLOGY/PRINCIPAL FINDINGS: In a 2-year experiment, we observed effective pollen dispersal from source populations of Centaurea jacea in restored meadows, the most widespread Swiss agri-environment scheme, to potted plants in adjacent intensively managed meadows without other individuals of this species. Potted plants were put in replicated source populations at 25, 50, 100 m and where possible 200 m distance from these source populations. Pollen transfer among isolated plants was prevented by temporary bagging, such that only one isolated plant was accessible for flower visitors at any one time. Because C. jacea is self-incompatible, seed set in single-plant isolates indicated insect mediated effective pollen dispersal from the source population. Seed set was higher in source populations (35.7+/-4.4) than in isolates (4.8+/-1.0). Seed set declined from 18.9% of that in source populations at a distance of 25 m to 7.4% at 200 m. At a distance of 200 m seed set was still significantly higher in selfed plants, indicating long-distance effective pollen dispersal up to 200 m. Analyses of covariance suggested that bees contributed more than flies to this long-distance pollen dispersal. We found evidence that pollen dispersal to single-plant isolates was positively affected by the diversity and flower abundance of neighboring plant species in the intensively managed meadow. Furthermore, the decline of the dispersal was less steep when the source population of C. jacea was large. CONCLUSIONS: We conclude that insect pollinators can effectively transfer pollen from source populations of C. jacea over at least 200 m, even when "recipient populations" consisted of single-plant isolates, suggesting that gene flow by pollen over this distance is very likely. Source population size and flowering environment surrounding recipient plants appear to be important factors affecting pollen dispersal in C. jacea. It is conceivable that most insect-pollinated plants in a network of restored sites within intensively managed grassland can form metapopulations, if distances between sites are of similar magnitude as tested here
Experimental investigation of micrometeorological influences on birch pollen emission
No full textDiseases due to aeroallergens constantly increased over the last decades and affect more and more people. Adequate protective and pre-emptive measures require both reliable assessment of production and release of various pollen species, and the forecasting of their atmospheric dispersion. Pollen forecast models, which may be either based on statistical knowledge or full physical transport and dispersion modeling, can provide pollen forecasts with full spatial coverage. Such models are currently being developed in many countries. The most important shortcoming in these pollen transport systems is the description of emissions, namely the dependence of the emission rate on physical processes such as turbulent exchange or mean transport and biological processes such as ripening (temperature) and preparedness for release. Thus the quantification of pollen emissions and determination of the governing mesoscale and micrometeorological factors are subject of the present project MicroPoem, which includes experimental field work as well as numerical modeling. The overall goal of the project is to derive an emission parameterization based on meteorological parameters, eventually leading to enhanced pollen forecasts. In order to have a well-defined source location, an isolated birch pollen stand was chosen for the set-up of a ‘natural tracer experiment', which was conducted during the birch pollen season in spring 2009. The site was located in a broad valley, where a mountain-plains wind system usually became effective during clear weather periods. This condition allowed to presume a rather persistent wind direction and considerable velocity during day- and nighttime. Several micrometeorological towers were operated up- and downwind of this reference source and an array of 26 pollen traps was laid out to observe the spatio-temporal variability of pollen concentrations. Additionally, the lower boundary layer was probed by means of a sodar and a tethered balloon system (also yielding a pollen concentration profile). The concentration distribution downwind of the birch stand exhibits a significant spatial (and temporal) variability. Small-scale numerical dispersion modeling will be used to infer the emission characteristics that optimally explain the observed concentration patterns
MicroPoem: experimental investigation of birch pollen emissions
No full textDiseases due to aeroallergens constantly increased over the last decades and affect more and more people. Adequate protective and pre-emptive measures require both reliable assessment of production and release of various pollen species, and the forecasting of their atmospheric dispersion. Pollen forecast models, which may be either based on statistical knowledge or full physical transport and dispersion modeling, can provide pollen forecasts with full spatial coverage. Such models are currently being developed in many countries. The most important shortcoming in these pollen transport systems is the description of emissions, namely the dependence of the emission rate on physical processes such as turbulent exchange or mean transport and biological processes such as ripening (temperature) and preparedness for release. Thus the quantification of pollen emissions and determination of the governing mesoscale and micrometeorological factors are subject of the present project MicroPoem, which includes experimental field work as well as numerical modeling. The overall goal of the project is to derive an emission parameterization based on meteorological parameters, eventually leading to enhanced pollen forecasts. In order to have a well-defined source location, an isolated birch pollen stand was chosen for the set-up of a ‘natural tracer experiment', which was conducted during the birch pollen season in spring 2009. The site was located in a broad valley, where a mountain-plains wind system usually became effective during clear weather periods. This condition allowed to presume a rather persistent wind direction and considerable velocity during day- and nighttime. Several micrometeorological towers were operated up- and downwind of this reference source and an array of 26 pollen traps was laid out to observe the spatio-temporal variability of pollen concentrations. Additionally, the lower boundary layer was probed by means of a sodar and a tethered balloon system (also yielding a pollen concentration profile). In the present contribution a project overview is given and first results are presented. An emphasis is put on the relative performance of different sample technologies and the corresponding relative calibration in the lab and the field. The concentration distribution downwind of the birch stand exhibits a significant spatial (and temporal) variability. Small-scale numerical dispersion modeling will be used to infer the emission characteristics that optimally explain the observed concentration patterns
Perspectives on deciphering mechanisms underlying plant heat stress response and thermotolerance
No full textGlobal warming is a major threat for agriculture and food safety and in many cases the negative effects are already apparent. The current challenge of basic and applied plant science is to decipher the molecular mechanisms of heat stress response (HSR) and thermotolerance in detail and use this information to identify genotypes that will withstand unfavorable environmental conditions. Nowadays X-omics approaches complement the findings of previous targeted studies and highlight the complexity of HSR mechanisms giving information for so far unrecognized genes, proteins and metabolites as potential key players of thermotolerance. Even more, roles of epigenetic mechanisms and the involvement of small RNAs in thermotolerance are currently emerging and thus open new directions of yet unexplored areas of plant HSR. In parallel it is emerging that although the whole plant is vulnerable to heat, specific organs are particularly sensitive to elevated temperatures. This has redirected research from the vegetative to generative tissues. The sexual reproduction phase is considered as the most sensitive to heat and specifically pollen exhibits the highest sensitivity and frequently an elevation of the temperature just a few degrees above the optimum during pollen development can have detrimental effects for crop production. Compared to our knowledge on HSR of vegetative tissues, the information on pollen is still scarce. Nowadays, several techniques for high-throughput X-omics approaches provide major tools to explore the principles of pollen HSR and thermotolerance mechanisms in specific genotypes. The collection of such information will provide an excellent support for improvement of breeding programs to facilitate the development of tolerant cultivars. The review aims at describing the current knowledge of thermotolerance mechanisms and the technical advances which will foster new insights into this process
Pollen physiology and fertilisation in Vicia Faba L
No full textAbstract In many legume crop species, early-formed fruits or those located closest to the photosynthate are more likely to mature than other fruits. This is so in the Vicia faba crop. Based on physiological, nutritional and genetical aspects of seed development, several hypotheses are documented. However, Vicia faba pollen fertility has not been adequately studied. Thus, a series of experiments, consisting of studies of both in vitro and in vivo pollen viability, pollen tube growth and fertilisation ability were conducted using highly inbred lines (6-13 generations). Some of the in vivo experiments were conducted under Ethiopian field conditions. In some lines, even a low level of stress at 20 ºC for 4h at 100% relative humidity (RH) caused a dramatic drop in mean percent pollen germination. The overall results indicated that there was considerable variation (p≥0.001) among the Hues studied, in response to high temperature (20 to 35 C) and 100% RH. Vicia faba pollen showed high variability in fertility level. Overall significant differences exist in fertility (p≥0.01) among the genotypes studied. A fertility gradient exists along the stem: in most genotypes the fertility declining towards the upper nodes. In all of the genotypes, the first nodes carried more highly fertile pollen than the middle and the last flowering nodes. Also the middle nodes were more highly productive than the last nodes in all the genotypes. Thus, success of fertilisation depends to a degree on the source of pollen used. In an experiment concerning pollen storage, freshly dehiscent anthers desiccated at 25 C/6h and freeze dried for 45min, stored in either LN2 or at -80 ºC, gave more than 80% viability after 9 months of storage. Desiccation at RT for 24h and storage in either LN2 or at -80 C and at -20 C, still maintained pollen viability ≥80%. Mixed pollination studies conducted indicated that pollen from one or other of each pair of inbred fines, mixed on an equal weight basis, performed better as pollen parents on some maternal fines than on others. The importance of these findings with respect to synthetic variety and hybrid seed production in the text is discussed. The probable existence of genetic self-incompatibility is also discussed
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Effects of post-translational modifications catalysed by pollen transglutaminase on the functional properties of microtubules and actin filaments
No full textTGases (transglutaminases) are a class of calcium-dependent enzymes that catalyse the interactions between acyl acceptor glutamyl residues and amine donors, potentially making crosslinks between proteins. To assess the activity of apple (Malus domestica) pollen TGase on the functional properties of actin and tubulin, TGase was prepared from apple pollen by hydrophobic interaction chromatography and assayed on actin and tubulin purified from the same cell type. The enzyme catalysed the incorporation of putrescine in the cytoskeleton monomers. When tested on actin filaments, pollen TGase induced the formation of high-molecular-mass aggregates of actin. Use of fluorescein– cadaverine showed that the labelled polyamine was incorporated into actin by pollen TGase, similar to with guinea pig liver TGase. The pollen TGase also reduced the enzyme activity and the binding of myosin to TGase-treated actin filaments. Polymerization of tubulin in the presence of pollen TGase also yielded the formation of high molecular mass aggregates. Furthermore, the pollen TGase also affected the binding of kinesin to microtubules and reduced the motility of microtubules along kinesincoated slides. These results indicate that the pollen tube TGase can control different properties of the pollen tube cytoskeleton (including the ability of actin and tubulin to assemble and their interaction with motor proteins) and consequently regulate the development of pollen tubes
Pollen characterisation of Maltese honey
No full textIn 2004 and 2005, pollen characterisation of 35 samples of honey collected from the islands of Malta and Gozo, was carried out with the aim to identify the botanical origin of honey produced on these islands. Pollen was extracted from the honey samples via centrifugation and identified to pollen type, generic level and where possible, specific level via microscopic analysis. This was done by comparison with available literature and with the aid of prepared reference slides of pollen collected from the plant species commonly present in the Maltese islands. A total of 61 pollen types were identified from 33 families. The best represented families were the Asteraceae, Brassicaceae, Fabaceae and Apiaceae. Thyme (Thymbra capitata (L.) CAV.) pollen was found to be predominant in ten samples, with a percentage frequency that ranged from 10\% to 67\%. Hedysarum coronarium L. was found to be predominant in five honey samples with percentage frequencies from 48\% to 78\% while Lotus spp. pollen was found to be predominant in one honey sample with a percentage frequency of 57\%. The remaining 14 honey samples possessed pollen spectra which were characterized by a few frequent pollen types that possessed similar percentage frequencies and were thus considered to be multifloral. This is the first work of pollen characterisation of Maltese honey.peer-reviewe
Observations and modelling of birch pollen emission and dispersion from an isolated source
No full textThe occurrence of allergic diseases in western countries increased during the last decades due to
greater awareness towards a hygienic lifestyle. The hygiene hypothesis relates the reduced expo-
sure to microbial pollution to an underdevelopment of the immune system, which in turn favours
the development of allergies. In order to provide information to affected individuals on adequate
pre-emptive measures, numerous studies on the health impact of allergenic pollen focus on their
atmospheric abundance and dispersion, including observations and simulation of emission and
transport. Prognostic models for the spatial distribution and concentration of different pollen
species on a regional scale are operational in many countries in order to identify highly affected
regions and allow health offices to announce warnings to the affected population. These models
are capable of predicting long-range transport in a full spatial resolution with respect to meteoro-
logical conditions. However, the initial abundance of airborne pollen in the models is determined
with empirically derived emission parameters, which are mostly based on long-term observation
averages with respect to large areas.
Field measurements and modelling work conducted in the framework of this thesis aimed at de-
scribing the emission and dispersion characteristics of an isolated natural birch pollen source in the
micro-scale, in order to improve the accuracy of the emission part in prognostic pollen transport
models. The basic approach was to infer the emission of the pollen source from downwind obser-
vations, with respect to meteorological conditions, by reproducing the observed pollen dispersion
with numerical simulations. Birch pollen are used, because they are among the most important
aeroallergens in Europe. In terms of quantifying the absolute pollen emission in speciffic cases,
however, the field observations of pollen concentrations were subject to various difficulties related
to sensor uncertainties and non-stationary conditions in the natural environment.
Firstly, the detailed investigation of pollen transport up- and downwind of the isolated source
relied on a large array of different instruments. In order to make the observations of birch pollen
concentrations comparable among different used instruments, a substantial part of this thesis is
dedicated to the description of performance and uncertainty of different pollen sampling methods.
Secondly, since naturally emitted pollen are used for tracers, instead of a controlled release of
artifficial particles, the observed pollen concentration can be biased by natural background con-
centration, which relates to emission from unknown sources upwind of the experiment site. The
wind
ow directed towards the birch canopy is substantially disturbed by its roughness and, addi-
tionally, a certain amount of airborne pollen is filtered by its vegetation elements. Observations
of undisturbed concentrations upwind of the windbreak thus fall short of describing the complex
pattern of downwind distribution. A computational
uid dynamics model, therefore, is used to
simulate Lagrangian-based trajectories of the pollen with respect to the disturbance of the wind
field. The results indicate that the portion of background concentration in the observed downwind
concentration is largely dependent on effects of accumulation due to deceleration of the wind
ow.
Deposition within the birch canopy is accounted for in a separate model, which is based on the
optical porosity of the windbreak. A combination of the two model approaches allows to eliminate
the portion of background concentration from the measured downwind concentrations, providing
information on the emissivity of the isolated birch pollen source.
Based on the corrected concentrations downwind of the windbreak, i.e. un-biased by background
concentration, a method of estimating the source strength of the isolated pollen source with a
Lagrangian particle model is assessed
Effects of Alternaria alternata f.sp. lycopersici toxins on pollen
No full textEffects of the phytotoxic compounds (AAL-toxins) isolated from cell-free culture filtrates of Alternaria alternata f.sp. lycopersici on in vitro pollen development were studied. AAL-toxins inhibited both germination and tube growth of pollen from several Lycopersicon genotypes. Pollen from susceptible genotypes, however, was more sensitive for AAL-toxins than pollen from resistant plants, while pollen of species not belonging to the host range of the fungus was not significantly affected by the tested toxin concentrations. AAL-toxins elicit symptoms in detached leaf bioassays indistinguishable from those observed on leaves of fungal infected tomato plants, and toxins play a major role in the pathogenesis. Apparently, pathogenesis-related processes and mechanisms involved in disease resistance are expressed in both vegetative and generative tissues. This overlap in gene expression between the sporophytic and gametophytic level of a plant may be advantageously utilized in plant breeding programmes. Pollen may be used to distinguish susceptible and resistant plants and to select for resistances and tolerances against phytotoxins and other selective agents.
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