Abstract: A progressive global increase in the burden of allergic diseases has affected the industrialized world over the last half century and has been reported in the literature. The clinical evidence reveals a general increase in both incidence and prevalence of respiratory diseases, such as allergic rhinitis (common hay fever) and asthma. Such phenomena may be related not only to air pollution and changes in lifestyle, but also to an actual increase in airborne quantities of allergenic pollen. Experimental enhancements of carbon dioxide (CO2) have demonstrated changes in pollen amount and allergenicity, but this has rarely been shown in the wider environment. The present analysis of a continental-scale pollen data set reveals an increasing trend in the yearly amount of airborne pollen for many taxa in Europe, which is more pronounced in urban than semi-rural/rural areas. Climate change may contribute to these changes, however increased temperatures do not appear to be a major influencing factor. Instead, we suggest the anthropogenic rise of atmospheric CO2 levels may be influential.

Abstract: . The ice nucleation of bioaerosols (bacteria, pollen, spores, etc.) is a topic of growing interest, since their impact on ice cloud formation and thus on radiative forcing, an important parameter in global climate, is not yet fully understood. Here we show that pollen of different species strongly differ in their ice nucleation behaviour. The average freezing temperatures in laboratory experiments range from 240 to 255 K. As the most efficient nuclei (silver birch, Scots pine and common juniper pollen) have a distribution area up to the Northern timberline, their ice nucleation activity might be a cryoprotective mechanism. Far more intriguingly, it has turned out that water, which has been in contact with pollen and then been separated from the bodies, nucleates as good as the pollen grains themselves. The ice nuclei have to be easily-suspendable macromolecules located on the pollen. Once extracted, they can be distributed further through the atmosphere than the heavy pollen grains and so presumably augment the impact of pollen on ice cloud formation even in the upper troposphere. Our experiments lead to the conclusion that pollen ice nuclei, in contrast to bacterial and fungal ice nucleating proteins, are non-proteinaceous compounds.

Abstract: The pollen tube is a cellular protuberance formed by the pollen grain, or male gametophyte, in flowering plants. Its principal metabolic activity is the synthesis and assembly of cell wall material, which must be precisely coordinated to sustain the characteristic rapid growth rate and to ensure geometrically correct and efficient cellular morphogenesis. Unlike other model species, the cell wall of the Arabidopsis (Arabidopsis thaliana) pollen tube has not been described in detail. We used immunohistochemistry and quantitative image analysis to provide a detailed profile of the spatial distribution of the major cell wall polymers composing the Arabidopsis pollen tube cell wall. Comparison with predictions made by a mechanical model for pollen tube growth revealed the importance of pectin deesterification in determining the cell diameter. Scanning electron microscopy demonstrated that cellulose microfibrils are oriented in near longitudinal orientation in the Arabidopsis pollen tube cell wall, consistent with a linear arrangement of cellulose synthase CESA6 in the plasma membrane. The cellulose label was also found inside cytoplasmic vesicles and might originate from an early activation of cellulose synthases prior to their insertion into the plasma membrane or from recycling of short cellulose polymers by endocytosis. A series of strategic enzymatic treatments also suggests that pectins, cellulose, and callose are highly cross linked to each other.

Abstract: Like many other bees worldwide, honeybees and bumblebees are threatened by human-induced disturbances. Yet some species decline and others thrive, likely due to different foraging strategies. As little is known about how resource intake translates into nutrients available to colonies, our study aimed to better understand how differences in foraging strategies may affect colony health by relating differences in pollen spectra collected to differences in nutrient composition. The Apis and Bombus colonies studied were all located at the same site, but nevertheless differed in the spectra of plant species visited for pollen collection and the quality of pollen collected. Bumblebees generally collected pollen with significantly higher pollen protein content and more essential amino acids. Unlike honeybees that tend to exploit large resource patches, bumblebees thus seem to select the “better” pollen and to focus on quality instead of quantity.

Abstract: There has been recent interest in the threat to bees posed by the use of systemic insecticides. One concern is that systemic insecticides may translocate from the soil into pollen and nectar of plants, where they would be ingested by pollinators. This paper reports on the movement of two such systemic neonicotinoid insecticides, imidacloprid and thiamethoxam, into the pollen and nectar of flowers of squash (Cucurbita pepo cultivars “Multipik,” “Sunray” and “Bush Delicata”) when applied to soil by two methods: (1) sprayed into soil before seeding, or (2) applied through drip irrigation in a single treatment after transplant. All insecticide treatments were within labeled rates for these compounds. Pollen and nectar samples were analyzed using a standard extraction method widely used for pesticides (QuEChERS) and liquid chromatography mass spectrometric analysis. The concentrations found in nectar, 10±3 ppb (mean ± s.d) for imidacloprid and 11±6 ppb for thiamethoxam, are higher than concentrations of neonicotinoid insecticides in nectar of canola and sunflower grown from treated seed, and similar to those found in a recent study of neonicotinoids applied to pumpkins at transplant and through drip irrigation. The concentrations in pollen, 14±8 ppb for imidacloprid and 12±9 ppb for thiamethoxam, are higher than those found for seed treatments in most studies, but at the low end of the range found in the pumpkin study. Our concentrations fall into the range being investigated for sublethal effects on honey bees and bumble bees.

Abstract: Neonicotinoids are systemic insecticides widely used on many pollinated agricultural crops, and increasing evidence indicates that they move to some extent into pollen and nectar. This study measured levels of neonicotinoid residues in pollen and nectar from a pumpkin crop treated with formulated products containing imidacloprid, dinotefuran, and thiamethoxam using different timings and application methods. Environmental conditions have a significant effect on overall residue levels; nectar residues were 73.5–88.8% less than pollen residues, and metabolites accounted for 15.5–27.2% of the total residue amounts. Foliar-applied treatments and chemigated insecticides applied through drip irrigation during flowering resulted in the highest residues of parent insecticide and metabolites, which may reach average levels up to 122 ng/g in pollen and 17.6 ng/g in nectar. The lowest levels of residues were detected in treatment regimens involving applications of insecticides at planting, as either seed dressing, be...

Abstract: Background Previous studies report associations between aeroallergen exposure and asthma exacerbations. Aeroallergen burdens and asthma prevalence are increasing worldwide and are projected to increase further with climate change, highlighting the importance of understanding population-level relationships between ambient pollen concentrations and asthma. Objective We sought to examine short-term associations between ambient concentrations of various pollen taxa and emergency department (ED) visits for asthma and wheeze in the Atlanta metropolitan area between 1993 and 2004. Methods We assessed associations between the 3-day moving average (lag 0-1-2) of Betulaceae (except Alnus species), Cupressaceae, Quercus species, Pinaceae (except Tsuga species), Poaceae, and Ambrosia species pollen concentrations and daily asthma and wheeze ED visit counts, controlling for covarying pollen taxa and ambient pollutant concentrations. Results We observed a 2% to 3% increase in asthma- and wheeze-related ED visits per SD increase in Quercus species and Poaceae pollen and a 10% to 15% increased risk on days with the highest concentrations (comparing the top 5% of days with the lowest 50% of days). An SD increase in Cupressaceae concentrations was associated with a 1% decrease in ED visits. The association for Quercus species pollen was strongest for children aged 5 to 17 years. Effects of Ambrosia species pollen on asthma exacerbations were difficult to assess in this large-scale temporal analysis because of possible confounding by the steep increase in circulating rhinoviruses every September. Conclusion Poaceae and Quercus species pollen contribute to asthma morbidity in Atlanta. Altered Quercus species and Poaceae pollen production caused by climate change could affect allergen-induced asthma morbidity in the southeastern United States.

Abstract: Since the primordial of humanity, pollen has been considered a good source of nutrients and energy. Its promising healing properties have also been referred to. The present study aimed to characterize, for the first time, eight commercial pollens from Portugal and Spain available on the market studying the legislation on labeling, pollinic origin, physicochemical and microbiological analyses and identification of yeasts. Eleven botanical families were found amongst the samples. The most abundant family and the most dominant pollen was Cistaceae. The moisture content, ash, aw, pH, reducing sugars, carbohydrates, proteins, lipids and energy were analyzed and the specific parameters were within the specifications required by some countries with legislation regarding these parameters. Microbiologically commercial pollen showed acceptable safety for the commercial quality and hygiene. All samples showed negative results for toxigenic species. The microorganisms studied were aerobic mesophiles, yeasts and moulds, coliforms, Escherichia coli, Staphylococcus aureus, Salmonella and sulfite-reducing Clostridium. During the work, six yeasts species were isolated from pollen, with Rhodotorula mucilaginosa being the most abundant, as it was present in four samples.

Abstract: A high-resolution record of Holocene environmental and climatic change in the Balikun area was reconstructed from a sediment core from the Lake Balikun Multiproxy data show that the climate was extremely arid during the early Holocene (before 86 cal ka BP) Moisture began to increase after 86 cal ka BP and the climate was humid between 79 and 43 cal ka BP A significant dry event occurred around 43–38 cal ka BP The climate became generally wet during the late Holocene (after 38 cal ka BP) The Holocene pollen and geophysical records do not indicate a wet early Holocene, making it evident that there was no early-Holocene humid period associated with peak Asian monsoon strength Regional comparisons indicate that this region has a different pattern of Holocene environmental and climatic change from the Asian monsoonal area and south Siberia

Abstract: SummaryBackground Few studies have focused on the role of grass pollen on asthma emergency department (ED) presentations among children. None have examined whether a dose-response effect exists between grass pollen levels and these asthma exacerbations. Objectives To examine the association between increasing ambient levels of grass pollen and asthma ED presentations in children. To determine whether these associations are seen only after a thunderstorm, or whether grass pollen levels have a consistent influence on childhood asthma ED visits during the season. Methods A short time series ecological study was conducted for asthma presentations to ED among children in Melbourne, Victoria, and grass pollen, meteorological and air quality measurements recorded during the selected 2003 period. A semi-parametric Poisson regression model was used to examine dose-response associations between daily grass pollen levels and mean daily ED attendance for asthma. Results A smoothed plot suggested a dose-response association. As ambient grass pollen increased to about 19 grains/m3, the same day risk of childhood ED presentations also increased linearly (P < 0.001). Grass pollen levels were also associated with an increased risk in asthma ED presentations on the following day (lag 1, P < 0.001). Conclusion This is the first study to establish a clear relationship between increased risk of childhood asthma ED attendance and levels of ambient grass pollen below 20 grains/m3, independent of any impact of thunderstorm-associated asthma. These findings have important implications for patient care, such as asthma management programs that notify the general public regarding periods of high grass pollen exposure, as well as defining the timing of initiation of pollen immunotherapy.

Abstract: Background Pollutants may affect pollen allergenicity and thus the prevalence of allergies. Although a few studies are available in literature, the connection between pollution and the allergenic potential of pollen has yet to be clearly defined. The objective of this study was to evaluate the effect of traffic-related pollution on the allergenicity of ragweed (Ambrosia artemisiifolia L.) pollen through a field-based experiment. Methods Mature pollen grains were collected from ragweed plants grown along main roadsides and in vegetated areas of Po river plain. The percentage of sub-pollen particle-releasing grains (SPPGs) was evaluated immediately after sampling by microscope and image analysis. Immunochemistry and LC-MS/MS were applied to assess the whole allergenicity and the allergen pattern characterizing the different pollen samples. Results No statistical difference was detected in the percentage of SPPGs among pollen samples. Specifically, after hydration, the mean percentage was very low (<4%) in all the samples, regardless of the site of origin. On the contrary, pollen collected along high-traffic roads showed a higher whole allergenicity than pollen from low-traffic roads and vegetated areas which showed a reactivity similar to that of the commercial pollen ‘Allergon’, used as a standard. The detected higher allergenicity levels were attributed to both quantitative and qualitative differences in allergen pattern. Conclusion Our findings show that pollen collected at different sites contains different amount and number of allergens and suggest that traffic-related pollution enhances ragweed pollen allergenicity, which may contribute to the increasing prevalence of ragweed allergy in Lombardy plain.

Abstract: Sexual reproduction in flowering plants is unique in multiple ways. Distinct multicellular gametophytes contain either a pair of immotile, haploid male gametes (sperm cells) or a pair of female gametes (haploid egg cell and homodiploid central cell). After pollination, the pollen tube, a cellular extension of the male gametophyte, transports both male gametes at its growing tip and delivers them to the female gametes to affect double fertilization. The pollen tube travels a long path and sustains its growth over a considerable amount of time in the female reproductive organ (pistil) before it reaches the ovule, which houses the female gametophyte. The pistil facilitates the pollen tube's journey by providing multiple, stage-specific, nutritional, and guidance cues along its path. The pollen tube interacts with seven different pistil cell types prior to completing its journey. Consequently, the pollen tube has a dynamic gene expression program allowing it to continuously reset and be receptive to multiple pistil signals as it migrates through the pistil. Here, we review the studies, including several significant recent advances, that led to a better understanding of the multitude of cues generated by the pistil tissues to assist the pollen tube in delivering the sperm cells to the female gametophyte. We also highlight the outstanding questions, draw attention to opportunities created by recent advances and point to approaches that could be undertaken to unravel the molecular mechanisms underlying pollen tube-pistil interactions.

Abstract: Within modern gymnosperms, conifers and Ginkgo are exclusively wind pollinated whereas many gnetaleans and cycads are insect pollinated. For cycads, thrips are specialized pollinators. We report such a specialized pollination mode from Early Cretaceous amber of Spain, wherein four female thrips representing a genus and two species in the family Melanthripidae were covered by abundant Cycadopites pollen grains. These females bear unique ring setae interpreted as specialized structures for pollen grain collection, functionally equivalent to the hook-tipped sensilla and plumose setae on the bodies of bees. The most parsimonious explanation for this structure is parental food provisioning for larvae, indicating subsociality. This association provides direct evidence of specialized collection and transportation of pollen grains and likely gymnosperm pollination by 110–105 million years ago, possibly considerably earlier.

Abstract: Habitat fragmentation can significantly affect mating and pollen dispersal patterns in plant populations, although the differential effects of the various aspects of fragmentation are poorly understood. In this study, we used eight microsatellite loci to investigate the effect of fragmentation on the mating system and pollen dispersal within one large and eight small population remnants of Banksia sphaerocarpa var. caesia, a bird-pollinated shrub in the southern agricultural region of Western Australia. The large population had a much larger neighbourhood size and lower selfing rate, maternal pollen pool differentiation and within-plot mean pollen dispersal distance than the small populations. Outcrossing was consistently high and ranged from 85.7% ± 2.6 to 98.5% ± 0.9, and mating patterns suggested nearest-neighbour pollination. Pollen immigration into small populations ranged from 2.8% ± 1.8 to 16.5% ± 3.2. Using the small populations, we tested for correlations between various fragmentation variables and mating system and pollen dispersal parameters. We found significant negative linear relationships between population isolation and outcrossing rate; population shape and neighbourhood size; and conspecific density and mean pollen dispersal distance. There were significant positive linear relationships between population shape and pollen pool differentiation and between population size and number of different fathers per seed crop. Our results suggest that birds may use a series of fragmented populations as a vegetation corridor while foraging across the landscape and that population connectivity is a critical determinant of pollinator visitation. Our results also suggest that the effect of a linear population shape on the mating system and pollen dispersal is routinely underestimated.

Abstract: Common ragweed (Ambrosia artemisiifolia L.) is a highly allergenic plant that is spreading throughout Europe. Ragweed pollen can be transported over large distances by the wind. Even low pollen concentrations of less than 10 pollen m−3 can lead to health problems in sensitive persons. Therefore, forecasting the airborne concentrations of ragweed pollen is becoming more and more important for public health. The question remains whether distant pollen sources need to be considered in reliable forecasts. We used the extended numerical weather prediction system COSMO-ART to simulate the release and transport of ragweed pollen in central Europe. A pollen episode (September 12–16, 2006) in north-eastern Germany was modeled in order to find out where the pollen originated. For this purpose, several different source regions were taken into account and their individual impact on the daily mean pollen concentration and the performance of the forecast were studied with the means of a 2 × 2 contingency table and skill scores. It was found that the majority of the pollen originated in local areas, but up to 20% of the total pollen load came from distant sources in Hungary. It is concluded that long-distance transport should not be neglected when predicting pollen concentrations.

Abstract: Pollen from a series of surface soil samples collected along a transect spanning southeast China was investigated to better understand palynological signals of ancient agriculture and other human a...

Abstract: Successful pollination depends on cell-cell communication and rapid cellular responses. In Arabidopsis, the pollen grain lands on a dry stigma, where it hydrates, germinates and grows a pollen tube that delivers the sperm cells to the female gametophyte to effect double fertilization. Various studies have emphasized that a mature, dehydrated pollen grain contains all the transcripts and proteins required for germination and initial pollen tube growth. Therefore, it is important to explore the role of post-translational modifications (here phosphorylation), through which many processes induced by pollination are probably controlled. We report here a phosphoproteomic study conducted on mature Arabidopsis pollen grains with the aim of identifying potential targets of phosphorylation. Using three enrichment chromatographies, a broad coverage of pollen phosphoproteins with 962 phosphorylated peptides corresponding to 598 phosphoproteins was obtained. Additionally, 609 confirmed phosphorylation sites were successfully mapped. Two hundred and seven of 240 phosphoproteins that were absent from the PhosPhAt database containing the empirical Arabidopsis phosphoproteome showed highly enriched expression in pollen. Gene ontology (GO) enrichment analysis of these 240 phosphoproteins shows an over-representation of GO categories crucial for pollen tube growth, suggesting that phosphorylation regulates later processes of pollen development. Moreover, motif analyses of pollen phosphopeptides showed an over-representation of motifs specific for Ca²⁺/calmodulin-dependent protein kinases, mitogen-activated protein kinases, and binding motifs for 14-3-3 proteins. Lastly, one tyrosine phosphorylation site was identified, validating the TDY dual phosphorylation motif of mitogen-activated protein kinases (MPK8/MPK15). This study provides a solid basis to further explore the role of phosphorylation during pollen development.

Abstract: The old calendar of pollens did not reflect current pollen distribution and concentrations that can be influenced by changes of weather and environment of each region in South Korea. A new pollen calendar of allergenic pollens was made based on the data on pollen concentrations obtained in eight regions nationwide between 1997 and 2009. The distribution of pollen was assessed every day at 8 areas (Seoul, Guri, Busan, Daegu, Jeonju, Kwangju, Kangneung, and Jeju) for 12 years between July 1, 1997 and June 30, 2009. Pollens were collected by using Burkard 7-day sampler (Burkard Manufacturing Co Ltd, UK). Pollens which were stained with Calberla's fuchsin staining solution were identified and counted. Pine became the highest pollen in May, and the pollen concentrations of oak and birch also became high. Ragweed appeared in the middle of August and showed the highest pollen concentration in the middles of September. Japanese hop showed a high concentration between the middle of August and the end of September, and mugwort appeared in the middles of August and its concentration increased up until early September. In Kangneung, birch appeared earlier, pine showed a higher pollen concentration than in the other areas. In Daegu, Oriental thuja and alder produced a large concentration of pollens. Pine produced a large concentration of pollens between the middle of April and the end of May. Weeds showed higher concentrations in September and mugwort appeared earlier than ragweed. In Busan the time of flowering is relatively early, and alder and Oriental thuja appeared earliest among all areas. In Kwangju, Oriental thuja and hazelnut appeared in early February. Japanese cedar showed the highest pollen concentration in March in Jeju. In conclusion, update information on pollen calendar in South Korea should be provided for allergic patients through the website to manage and prevent the pollinosis.

Abstract: Quercus species exhibit an extreme inter-annual variability in seed production often synchronized over large geographical areas (masting) Since this reproductive behavior is mostly observed in anemophilous plants, pollination efficiency is suggested as one hypothesis to explain it, although resource-based hypotheses are also suggested as alternatives We analyzed the effect of flowering phenology, airborne pollen presence and meteorological conditions in the pattern of acorn production in mixed evergreen-deciduous oak forests (Quercus ilex and Quercus pubescens) in NE Spain for twelve years (1998–2009) In both oaks, higher temperatures advanced the onset of flowering and increased the amount of airborne pollen Nevertheless, inter-annual differences in pollen production did not influence acorn crop size Acorn production was enhanced by a delay in flowering onset in Q ilex but not in Q pubescens This suggests that in perennial oaks a larger number of photosynthates produced before flowering could benefit reproduction while the lack of effects on deciduous oaks could be because these species flush new leaves and flowers at the same time Notwithstanding this effect, spring water deficit was the most relevant factor in explaining inter-annual variability in acorn production in both species Considering that future climate scenarios predict progressive warmer and dryer spring seasons in the Mediterranean Basin, this might result in earlier onsets of flowering and higher water deficits that would constrain acorn production

Abstract: Bee pollen is composed of floral pollen mixed with nectar and bee secretion that is collected by foraging honey (Apis sp.) and stingless bees. It is rich in nutrients, such as sugars, proteins, lipids, vitamins and flavonoids, and has been ascribed antiproliferative, anti-allergenic, anti-angiogenic and free radical scavenging activities. This research aimed at a preliminary investigation of the chemical constituents and free radical scavenging activity in A. mellifera bee pollen. Bee pollen was directly collected from A. mellifera colonies in Nan province, Thailand, in June, 2010, whilst floral corn (Zea mays L.) pollen was collected from the nearby corn fields. The pollen was then sequentially extracted with methanol, dichloromethane (DCM) and hexane, and each crude extract was tested for free radical scavenging activity using the DPPH assay, evaluating the percentage scavenging activity and the effective concentration at 50% (EC50). The most active crude fraction from the bee pollen was then further enriched for bioactive components by silica gel 60 quick and adsorption or Sephadex LH-20 size exclusion chromatography. The purity of all fractions in each step was observed by thin layer chromatography and the bioactivity assessed by the DPPH assay. The chemical structures of the most active fractions were analyzed by nuclear magnetic resonance. The crude DCM extract of both the bee corn pollen and floral corn pollen provided the highest active free radical scavenging activity of the three solvent extracts, but it was significantly (over 28-fold) higher in the bee corn pollen (EC50 = 7.42 ± 0.12 μg/ml), than the floral corn pollen (EC50 = 212 ± 13.6% μg/ml). After fractionation to homogeneity, the phenolic hydroquinone and the flavone 7-O-R-apigenin were found as the minor and major bioactive compounds, respectively. Bee corn pollen contained a reasonably diverse array of nutritional components, including biotin (56.7 μg/100 g), invert sugar (19.9 g/100 g), vitamin A and β carotene (1.53 mg/100 g). Bee pollen derived from corn (Z. mays), a non-toxic or edible plant, provided a better free radical scavenging activity than floral corn pollen.

Abstract: Pollen was analysed from a sediment sequence collected in the close vicinity of the Mesolithic settlement Tagerup, southern Sweden. Macroremains were also retrieved from numerous samples taken at the site of the archaeological excavations of Kongemose and Ertebolle settlement phases, 6700–6000 b.c. and 5500–4900 b.c. respectively. Plants and other organic remains were well preserved in the refuse layers from the settlements embedded in the gyttja. The pollen record includes no clear indications of human impact on the vegetation during the Mesolithic. The occurrence of charcoal particles and pollen of grass and herbs associated with nutrient-rich soils are contemporaneous with the Kongemose settlement. The Ertebolle settlement phase, although characterised by considerable dwelling activities less than a hundred metres from the pollen sampling site, is scarcely seen in the pollen data. Numerous finds of crushed dogwood stones from the Kongemose phase, often partly carbonised, suggest that these stones were used for the extraction of oil. Other plants found in the Kongemose refuse layers that may have been used are apples, cherries, raspberries, acorns and rowan-berries. Based on the abundance of hazelnut shells found at the studied site and in other studies of Mesolithic sites in southern Scandinavia it is proposed that these remains may testify to an important food supply rather than just use as a supplement to animal protein. It is also hypothesised that a regional decrease in hazel populations and thus hazelnut availability at the end of the Mesolithic may have motivated the adoption of Neolithic subsistence.

Abstract: Background: Pollutants may affect pollen allergenicity and thus the prevalence of allergies. Although a few studies are available in literature, the connection between pollution and the allergenic potential of pollen has yet to be clearly defined. The objective of this study was to evaluate the effect of traffic-related pollution on the allergenicity of ragweed (Ambrosia artemisiifolia L.) pollen through a field-based experiment. Methods: Mature pollen grains were collected from ragweed plants grown along main roadsides and in vegetated areas of Po river plain. The percentage of subpollen particle-releasing grains (SPPGs) was evaluated immediately after sampling by microscope and image analysis. Immunochemistry and LC-MS/MS were applied to assess the whole allergenicity and the allergen pattern characterizing the different pollen samples. Results: No statistical difference was detected in the percentage of SPPGs among pollen samples. Specifically, after hydration, the mean percentage was very low (<4%) in all the samples, regardless of the site of origin. On the contrary, pollen collected along high-traffic roads showed a higher whole allergenicity than pollen from low-traffic roads and vegetated areas which showed a reactivity similar to that of the commercial pollen ‘Allergon’, used as a standard. The detected higher allergenicity levels were attributed to both quantitative and qualitative differences in allergen pattern. Conclusion: Our findings show that pollen collected at different sites contains different amount and number of allergens and suggest that traffic-related pollution enhances ragweed pollen allergenicity, which may contribute to the increasing prevalence of ragweed allergy in Lombardy plain.

Abstract: Background and aims Exposure to higher-than-optimal temperatures reduces crop yield and quality, mainly due to sensitivity of developing pollen grains. The mechanisms maintaining high pollen quality under heat-stress conditions are poorly understood. Our recently published data indicate high heatstress-induced expression of ethylene-responsive genes in tomato pollen, indicating ethylene involvement in the pollen heat-stress response. Here we elucidated ethylene’s involvement in pollen heat-stress response and thermotolerance by assessing the effects of interfering with the ethylene signalling pathway and altering ethylene levels on tomato pollen functioning under heat stress. Methodology Plants of the ethylene-insensitive mutant Never ripe (Nr)—defective in an ethylene response sensor (ERS)-like ethylene receptor—and the corresponding wild type were exposed to control or heat-stress growing conditions, and pollen quality was determined. Starch and carbohydrates were measured in isolated pollen grains from these plants. The effect of pretreating cv. Micro-Tom tomato plants, prior to heat-stress exposure, with an ethylene releaser or inhibitor of ethylene biosynthesis on pollen quality was assessed. Principal results Never ripe pollen grains exhibited higher heat-stress sensitivity, manifested by a significant reduction in the total number of pollen grains, reduction in the number of viable pollen and elevation of the number of non-viable pollen, compared with wild-type plants. Mature Nr pollen grains accumulated only 40 % of the sucrose level accumulated by the wild type. Pretreatment of tomato plants with an ethylene releaser increased pollen quality under heat stress, with an over 5-fold increase in the number of germinating pollen grains per flower. Pretreatment with an ethylene biosynthesis inhibitor reduced the number of germinating pollen grains following heat-stress exposure over 5-fold compared with non-treated controls. Conclusions Ethylene plays a significant role in tomato pollen thermotolerance. Interfering with the ethylene signalling pathway or reducing ethylene levels increased tomato pollen sensitivity to heat stress, whereas increasing ethylene levels prior to heat-stress exposure increased pollen quality.