Fact-checked by Grok 2 weeks ago

Pollen

Pollen consists of microscopic grains produced by the anthers of seed plants, serving as the male gametophytes that carry genetic material for sexual reproduction in angiosperms and gymnosperms.^[1] Each pollen grain encapsulates two sperm cells within a protective structure, enabling fertilization upon reaching the female reproductive organs.^[2] The grains feature a durable outer wall composed primarily of sporopollenin, a highly resistant polymer that aids survival during dispersal and imparts species-specific morphological patterns useful for taxonomic identification.^[3] Upon compatible contact with a stigma or ovule, pollen grains germinate by extending a pollen tube that delivers the sperm cells to the egg for double fertilization, a process essential for seed and fruit development in flowering plants.^[4] Dispersal occurs via diverse mechanisms, including wind (anemophily) for lightweight grains in grasses and conifers, and biotic vectors such as insects, birds, and bats attracted by floral rewards in many angiosperms, with water facilitating transfer in select aquatic species.^[5] This reproductive strategy underpins global plant diversity, as pollen transfer directly enables seed production without which angiosperm propagation—and thus much of terrestrial ecosystems—would cease.01022-1) Pollen also profoundly impacts human health, acting as a primary aeroallergen that triggers allergic rhinitis (hay fever) and exacerbates asthma in susceptible individuals through immune-mediated inflammation upon inhalation.^[6] Symptoms include sneezing, congestion, and itchy eyes, affecting over 100 million people annually in the United States alone, with pollen seasons lengthening due to environmental factors.^[7]^[8] These grains' proteins, released during rupture in humid airways, provoke IgE antibody responses, underscoring pollen's dual role as both ecological cornerstone and public health challenge.^[9]

Biological Fundamentals

Definition and Composition

Pollen grains represent the male gametophytes of seed plants, including both gymnosperms and angiosperms, functioning as the primary vehicles for male gamete dispersal during sexual reproduction. Each grain develops from microspores produced via meiosis in the anthers of flowering plants or microsporangia of gymnosperms, encapsulating haploid cells essential for fertilization.01022-1)^[10] The structure of a mature pollen grain features a robust outer exine layer, predominantly composed of sporopollenin, a highly resistant biopolymer formed from polyhydroxyphenolic and polyacetategenolic compounds that confers durability against environmental degradation and enzymatic attack. This exine, often sculpted with species-specific apertures like pores or furrows, surrounds the softer intine layer made of cellulose, hemicellulose, and pectins, which facilitates pollen tube emergence. The protoplast within includes a large vegetative cell responsible for tube growth and a smaller generative cell that undergoes mitosis to yield two sperm cells.^[11]^[12] Chemically, pollen grains exhibit variable composition across species, with dry matter typically comprising 10-40% proteins, 1-20% lipids, and 10-50% carbohydrates in the cytoplasm, alongside minerals and trace vitamins; however, the exine dominates mass in many cases due to sporopollenin's inert nature and low solubility. Sporopollenin itself resists hydrolysis and oxidation, persisting in sediments for millions of years, underscoring its evolutionary role in land plant adaptation. These components enable pollen's role in reproduction while providing nutritional value to pollinators, though allergenicity arises from specific glycoproteins on the surface.^[13]^[14]

Development and Formation

Pollen grains originate in the microsporangia located within the anthers of angiosperms or the pollen cones of gymnosperms, where diploid microspore mother cells (also known as pollen mother cells) differentiate from sporogenous tissue.^[15] These cells undergo meiosis during microsporogenesis to produce haploid microspores arranged in tetrads, with the process typically occurring in the corners of the tetrasporangiate anther lobes.^[16] The surrounding tapetal layer, derived from the sporophytic tissue, provides nourishment and enzymes such as callase to facilitate microspore separation from the tetrad, while also contributing materials for pollen wall formation.^[17] In angiosperms, meiosis yields four haploid microspores per mother cell, enclosed initially by a callosic wall that is later degraded.^[18] Following microsporogenesis, each microspore undergoes microgametogenesis, transforming into a mature pollen grain through asymmetric mitotic divisions.^[19] The first mitosis produces a large vegetative (tube) cell and a smaller generative cell, which may undergo a second mitosis to form two sperm cells within the pollen grain or during tube growth; this results in the binucleate or trinucleate pollen typical of many angiosperm species.^[20] Concurrently, the pollen wall develops, featuring an outer exine layer composed of sporopollenin—a highly resistant polymer synthesized partly by the tapetum—providing protection against desiccation and UV radiation, while the inner intine layer forms from microspore-derived materials.^[21] Dehiscence of the anther occurs upon maturation, releasing pollen grains adapted for dispersal by wind, water, or biotic vectors.^[22] In gymnosperms, the process mirrors angiosperms in initiating with meiotic tetrads but often retains a persistent tetrad structure in some lineages, with microgametogenesis yielding multicellular pollen grains containing prothallial cells alongside generative and tube cells.^[18] Environmental factors, such as temperature and nutrient availability, influence the timing and synchrony of these developmental stages, with disruptions leading to male sterility in crops like rice and maize.^[18] Genetic regulation involves sporophytic genes for early phases and gametophytic genes for pollen maturation, underscoring the interplay between parental and progeny genomes.^[20]

Structure and Morphology

Pollen grains consist of a plasma membrane-enclosed protoplast surrounded by a multilayered wall, with the outer exine providing primary structural integrity and the inner intine offering flexibility.^[23] The exine, deposited during microspore development, is composed mainly of sporopollenin, a durable biopolymer resistant to chemical and biological degradation, enabling long-term preservation in sediments.^[23] This layer features intricate sculpturing, such as granules, spines, or reticulations, which vary taxonomically and aid in species identification via palynology.^[24] The intine, formed post-exine deposition, comprises cellulose, hemicellulose, and pectins, allowing dynamic remodeling during germination when the pollen tube emerges.^[25] Pollen grains typically measure 10 to 100 micrometers in diameter, with extremes like 6 μm in Myosotis species or up to 250 μm in some orchids, reflecting adaptations to dispersal and pollination strategies.^[26] Shapes range from spheroidal and oblate to prolate or triangular in polar view, often correlating with aperture configuration and phylogenetic lineage.^[27] Apertures—thinned or absent exine regions—facilitate hydration and tube protrusion, classified as sulcate (one meridional furrow, prevalent in gymnosperms and monocots), porate (circular pores), colpate (elongated furrows or colpi), or colporate (colpi with internal pores).^[28] Angiosperm pollen often exhibits 3–6 equatorial apertures in a zonocolporate pattern, enhancing germination efficiency, while gymnosperm pollen may lack complex apertures or feature sacs for wind dispersal buoyancy.^[24] Ornamentation and aperture density influence aerodynamic properties and pollinator interactions, with empirical studies linking larger grains under desiccation stress to thicker exines for protection.^[29]

Reproductive Processes

Pollination Mechanisms and Vectors

Pollination involves the transfer of pollen grains from the anther to the stigma, facilitating fertilization in seed plants. Mechanisms are broadly abiotic, relying on physical agents like wind or water, or biotic, mediated by animals. Among angiosperms, approximately 88% of species depend on animal vectors for pollination, with the proportion rising to 94% in tropical communities, while wind pollination accounts for about 10% of species globally.^[30]^[31] In anemophily, wind disperses lightweight pollen grains produced in enormous quantities—often billions per plant—to compensate for low precision in delivery. Anemophilous pollen is typically small (10-30 μm diameter), smooth-surfaced, and buoyant, with minimal ornamentation on the exine to reduce drag and enhance airborne longevity; shapes are often spheroidal or oblate spheroidal. Grasses, conifers, and many temperate trees exemplify this, where flowers lack showy attractants and release pollen synchronously during favorable wind conditions.^[32]^[33] Hydrophily, rarer and limited to aquatic plants like some seagrasses (e.g., Zostera species), involves pollen dispersal via water currents; pollen forms elongated, thread-like structures or mucilaginous masses that float or sink to stigmas submerged in marine or freshwater environments, comprising less than 1% of angiosperms.^[34] Biotic pollination, predominantly entomophily, features pollen adapted for adhesion to insect bodies. Entomophilous grains are medium-sized (20-50 μm), often oblate, with rough, spiny, or sticky exine sculpturing via protrusions like echinae or verrucae that promote electrostatic and mechanical attachment to hairs or cuticles. Plants produce fewer grains per flower but invest in nectar, scents, or visual cues to attract vectors such as bees (Hymenoptera), flies (Diptera), butterflies (Lepidoptera), and beetles (Coleoptera), which account for the majority of insect-mediated transfers. Vertebrate vectors like birds and bats handle larger, sticky pollen in specialized syndromes, though less common; pollen viability post-transfer relies on these adaptations to withstand desiccation and mechanical stress during vector movement.^[32]^[33]^[35]

Pollen Tube Dynamics and Fertilization

Upon compatible pollination, the pollen grain germinates on the stigma surface, extending a tubular outgrowth known as the pollen tube, which serves to transport the two immobile sperm cells toward the ovule for fertilization in angiosperms.^[36] This process begins with hydration of the pollen grain, triggering metabolic activation and rupture of the exine to allow protrusion of the tube from the aperture or germ pore.^[37] Pollen tube elongation occurs via polarized tip growth, where new membrane and cell wall materials are deposited at the apex through targeted secretion of vesicles along actin filaments.^[37] Cytoskeletal elements, including fine actin bundles and myosin motors, facilitate rapid vesicle trafficking, enabling growth rates up to several centimeters per hour in some species, such as those observed in lily where tubes extend over 30 cm.^[38] Intracellular signals, including oscillatory calcium gradients at the tip and reactive oxygen species (ROS), regulate this dynamics by coordinating exocytosis, endocytosis, and cell wall softening via pectin de-esterification.^[37]^[38] Guidance of the pollen tube involves multiple chemotropic cues secreted by female reproductive tissues, transitioning from stigma-derived signals for initial orientation to style-specific attractants and finally ovule-emitted molecules for precise targeting.^[39] In the style, extracellular matrix components and diffusible factors maintain directed growth, while near the ovule, small cysteine-rich proteins like LURE peptides in Torenia fournieri induce attraction specifically toward the micropyle.^[39] Recent imaging in Arabidopsis revealed one-to-one pollen tube-ovule pairing, with tubes emerging from the transmitting tract, growing along the funiculus, and slowing before micropylar entry, often completing the journey in under 4 hours post-germination.^[40]^[41] Upon reaching the female gametophyte, the pollen tube penetrates a synergid cell, bursts to release the sperm cells, initiating double fertilization unique to angiosperms.^[42] One sperm fuses with the egg cell to form the diploid zygote, precursor to the embryo, while the second fuses with the diploid central cell to produce the triploid endosperm, which nourishes the developing seed.^[42] This coordinated syngamy ensures endosperm formation only upon egg fertilization, preventing resource allocation to unfertilized ovules, with pollen tube rupture triggered by synergid degeneration and calcium influx.^[42]^[36] In gymnosperms, pollen tubes deliver sperm differently, often via siphonogamy without double fertilization, highlighting angiosperm-specific innovations.^[42]

Evolutionary History

Origins and Phylogenetic Distribution

Pollen originated with the evolution of seed plants (Spermatophyta) during the Late Devonian period, approximately 372 to 359 million years ago, marking a key adaptation for terrestrial reproduction independent of free water.^[43] Fossil evidence includes pollen organs such as Telangiopsis sp., associated with early seed plant fructifications, indicating the development of wind-dispersed male gametophytes in progymnosperm-like ancestors.^[44] These structures represent a transition from free-living gametophytes in earlier vascular plants to reduced, dispersal-resistant pollen grains enclosed within spore walls, enabling efficient transfer to ovules./5:_Biological_Diversity/26:_Seed_Plants/26.1:_Evolution_of_Seed_Plants) Phylogenetically, pollen production is a synapomorphy of the monophyletic clade Spermatophyta, encompassing all extant gymnosperms and angiosperms, which together comprise over 300,000 species dominating modern terrestrial ecosystems.^[45] Gymnosperms, including cycads (Cycadophyta), ginkgo (Ginkgophyta), conifers (Pinophyta), and gnetophytes (Gnetophyta), produce pollen with features like air bladders for wind dispersal, reflecting their basal position.^[46] Angiosperms (flowering plants, Magnoliophyta), which diversified rapidly in the Mesozoic, exhibit more varied pollen morphologies adapted to biotic vectors, but retain the core pollen tube mechanism for fertilization. Pollen is absent in non-seed vascular plants (pteridophytes, including ferns and lycophytes) and non-vascular bryophytes, where motile sperm require water for fertilization.^[47] This distribution underscores pollen's role in the adaptive radiation of seed plants, with no reversals to pre-pollen reproductive strategies in derived lineages, as evidenced by consistent microsporangial development across the clade.^[48]

Fossil Record and Paleopalynology

The exine of pollen grains, composed primarily of sporopollenin, confers exceptional resistance to chemical and biological degradation, enabling their preservation as microfossils in sedimentary rocks, peats, and amber deposits spanning hundreds of millions of years.^[49] Fossil pollen, or palynomorphs, are extracted via acid digestion techniques that isolate acid-resistant organic material from host sediments, allowing identification based on morphology such as aperture type, size (typically 10-100 micrometers), and surface sculpturing.^[50] Preservation is optimal in low-oxygen, acidic environments like anoxic lake bottoms or mires, where oxidative decay is minimized, though mechanical damage or thermal alteration can degrade diagnostic features.^[51] The earliest fossil pollen records originate from late Devonian seed plants, dating to approximately 372-359 million years ago (Ma) during the Famennian stage, associated with primitive progymnosperms and early pteridosperms (seed ferns) such as Elkinsia polymorpha.^[52] ^[53] These initial pollen grains were simple, often bisaccate or monosulcate, reflecting pre-gymnospermous dispersal mechanisms adapted to terrestrial environments. By the Carboniferous period (359-299 Ma), pollen diversity exploded with the proliferation of seed ferns and progymnosperms, providing biostratigraphic markers for coal-bearing strata and evidencing the radiation of vascular seed plants amid rising atmospheric oxygen levels.^[54] Gymnosperm pollen dominated Mesozoic records, with conifer-like bisaccate forms abundant in Triassic and Jurassic sediments; angiosperm pollen, characterized by tricolpate or porate apertures, first appears reliably in Early Cretaceous strata around 130 Ma, marking the diversification of flowering plants, though disputed monosulcate forms from Middle Triassic deposits (~240 Ma) have been proposed as precursors but lack consensus due to morphological overlap with gymnosperms.^[55] Post-Cretaceous records document shifts, such as Eocene pollen assemblages revealing early bird pollination (~47 Ma) via preserved grains in avian stomach contents.^[56] Paleopalynology applies these fossils to reconstruct paleoecology, stratigraphy, and climate, with pollen assemblages serving as proxies for vegetation composition and environmental shifts; for instance, Devonian-Carboniferous boundary spores indicate floral turnovers linked to potential UV-B radiation spikes or anoxic events.^[57] Quantitative analysis of pollen types, such as ratios of arboreal to herbaceous forms, infers past temperatures and precipitation, as seen in Paleocene grains reflecting post-K-Pg recovery of angiosperms.^[58] Evolutionary trends in pollen morphology—e.g., increasing complexity in aperture systems from Devonian simplicity to Cretaceous tricolpates—track phylogenetic transitions, aiding correlation of distant sedimentary basins via index species like Lycopodium spores or Callipollenites for Carboniferous dating.^[59] This discipline's empirical strength lies in its direct linkage of microfossil traits to macroevolutionary patterns, though biases in preservation favor wind-dispersed anemophilous taxa over entomophilous ones.^[60]

Ecological Roles

Interactions with Pollinators and Ecosystems

Pollen serves as a primary nutritional reward in mutualistic interactions between angiosperms and animal pollinators, particularly insects such as bees, which collect it for its high protein content essential for larval development and colony reproduction.^[61] Bee-collected pollen typically contains 2.5% to 61% protein by dry weight, with bees exhibiting preferences for pollen sources exceeding 20% protein to meet optimal dietary needs.^[62] This selective foraging behavior influences pollen transfer efficiency, as pollinators like honey bees (Apis mellifera) and bumble bees (Bombus spp.) inadvertently deposit pollen grains on stigmas while grooming or accessing floral resources.^[63] In ecosystems, these interactions underpin plant reproductive success and genetic diversity through pollen dispersal, which facilitates gene flow across populations and mitigates inbreeding depression in fragmented habitats.^[64] Pollinator diversity enhances ecosystem resilience to environmental perturbations by stabilizing pollination services, as diverse assemblages compensate for fluctuations in individual species' activity, thereby sustaining seed set and floral abundance.^[65] For instance, specialist pollinators may achieve higher pollen deposition per visit but limited dispersal distance, while generalists promote broader pollen movement, contributing to metapopulation dynamics in natural landscapes.^[66] Pollen also integrates into broader trophic networks, where its dispersal patterns serve as biomarkers for tracking plant-pollinator assemblage shifts amid habitat alterations, revealing declines in biodiversity linked to reduced pollen flow.^[63] Habitat fragmentation disrupts these mutualisms, leading to pollen limitation that curtails plant fitness and cascades to dependent herbivores and seed dispersers, underscoring pollen's role in maintaining ecosystem structure.^[67] Empirical studies indicate that pollinator losses, such as those from land-use intensification, diminish effective pollen transfer, exacerbating biodiversity erosion in both natural and agroecosystems.^[68]

Environmental Influences on Pollen Production

Temperature exerts a significant influence on pollen production, with optimal ranges varying by species but generally favoring moderate warmth for maximal output. Elevated temperatures associated with climate warming have been observed to extend pollen seasons and increase total emissions; for instance, projections indicate that temperature and precipitation changes could boost annual pollen emission by 16–40% in temperate regions. However, extreme heat, such as during heatwaves, impairs pollen development by reducing grain quantity and quality, leading to heightened pollen limitation in affected flowers. In maize, exposure to high temperatures during reproductive phases dramatically decreases seed production through abnormal pollen formation, with pollen sterility rates increasing under stresses exceeding 30–35°C.^[69]^[70]^[71] Atmospheric carbon dioxide concentrations directly enhance pollen production via fertilization effects on plant growth. In ragweed (Ambrosia artemisiifolia), exposure to elevated CO₂ levels (approximately 370 ppm compared to pre-industrial 280 ppm) increased pollen output by 131%, while projected future levels (around 600 ppm) could raise it by 320%, based on controlled chamber experiments. This response stems from CO₂ stimulating photosynthesis and biomass allocation to reproductive structures, though effects vary by species; some studies show minimal uniform changes in pollen chemistry across diverse flowering plants under doubled CO₂. Warmer temperatures compound this by further augmenting pollen loads in CO₂-enriched environments.^[72]^[73]^[74] Water availability critically modulates pollen production, with drought stress disrupting microsporogenesis and reducing viability. Under drought conditions, plants exhibit pollen sterility due to impaired carbohydrate metabolism and tapetum degeneration, as seen in wheat where water deficits lowered pollen fertility and grain yield. Combined drought and heat further diminish pollen shedding and silk receptivity in crops like corn, with stressed plants producing fewer viable grains despite occasional increases in pollen weight per hybrid. Precipitation patterns also influence emissions, with deficits shortening daily maxima by up to 40% while surpluses can elevate totals.^[75]^[76]^[69] Photoperiod and light intensity indirectly affect pollen production by regulating flowering phenology and resource allocation. Short-day plants delay flowering under extended photoperiods mimicking light pollution, potentially reducing overall reproductive output, while optimal light promotes pollen tube growth via enhanced photosynthesis. In controlled studies, photoperiod extensions increased fertile pollen yield in certain genotypes by up to significant margins over five years, highlighting its role in synchronizing pollen development with environmental cues.^[77]^[78]

Human Health and Nutrition

Allergenic Impacts and Immunology

Pollen grains contain water-soluble proteins that act as aeroallergens, triggering type I hypersensitivity reactions in sensitized individuals through IgE-mediated mechanisms. Upon inhalation, these allergens bind to IgE antibodies attached to high-affinity FcεRI receptors on mast cells and basophils, leading to degranulation and release of mediators such as histamine, leukotrienes, and cytokines, which cause symptoms like sneezing, rhinorrhea, nasal congestion, and ocular pruritus.^[79] Innate immune responses are also elicited by pollen components including proteases, lipids, and NADPH oxidases, which activate epithelial cells and dendritic cells to promote Th2-skewed adaptive immunity and allergen-specific IgE production.^[80] Sensitization typically begins with antigen presentation by nasal dendritic cells processing fragmented pollen proteins released upon grain rupture in humid airways.^[9] Major pollen allergens derive from trees, grasses, and weeds, with specific proteins dominating regional sensitivities. Tree pollens from orders Fagales (e.g., birch Bet v 1 homologs), Proteales, and Pinales contain pathogenesis-related proteins and profilins that cross-react across species; grass pollens feature group 1 and 5 allergens like Phl p 1 and Phl p 5 from timothy grass; weed pollens, particularly ragweed (Amb a 1), include pectate lyases and defensins.^[81] ^[82] These proteins exhibit structural similarities enabling cross-reactivity, such as between birch pollen and certain fruits in oral allergy syndrome, though primary sensitization occurs via respiratory exposure.^[83] Allergic rhinitis, commonly known as hay fever, affects 10-30% of adults and children in the United States and comparable nations, with seasonal pollen exposure driving episodic symptoms in over 40-60 million Americans annually.^[84] ^[85] Prevalence data indicate 25.7% of U.S. adults report seasonal allergies, higher in urban areas with elevated pollen counts, and symptoms exacerbate asthma in 20-30% of cases via eosinophilic inflammation and airway hyperresponsiveness.^[86] Key cytokines IL-4, IL-5, and IL-13 from Th2 cells and innate lymphoid cells amplify IgE synthesis and mucus production.^[87] Immunological tolerance can be induced via allergen immunotherapy (AIT), which shifts responses toward regulatory T cells and IgG4 blocking antibodies, suppressing seasonal IgE rises and Th2 activity.^[88] Evidence from birch and grass AIT trials shows reduced nasal symptoms and medication use persisting post-treatment, though efficacy varies by allergen dose and patient adherence.^[89] Rising CO2 and temperatures have extended pollen seasons by 20 days on average in North America since 1990, correlating with increased sensitization rates, though causal attribution requires controlling for urbanization and air pollution confounders.^[90]

Nutritional Properties and Evidence-Based Uses

Bee pollen, the aggregated pollen grains collected and processed by honeybees, exhibits a nutrient-dense profile that varies according to botanical origin, geographic region, and collection methods, with typical dry weight compositions including 10–40% protein, 13–55% carbohydrates, 1–13% lipids, 0.3–20% crude fiber, and 2–6% ash representing minerals.^[91] Proteins average 22.7% and encompass essential amino acids such as lysine, threonine, methionine, leucine, isoleucine, phenylalanine, and tryptophan, rendering it comparable to legume sources in amino acid completeness.^[92] ^[93] Carbohydrates predominate as simple sugars like fructose and glucose, while lipids feature polyunsaturated fatty acids including linoleic and alpha-linolenic acids.^[94] Micronutrients in bee pollen include fat-soluble vitamins such as provitamin A (beta-carotene), vitamins D and E at approximately 0.1% combined, and water-soluble vitamins comprising 0.6% including B1 (thiamine), B2 (riboflavin), B6 (pyridoxine), and C (ascorbic acid), alongside traces of folate and biotin.^[14] Mineral content is notable, with potassium, phosphorus, calcium, magnesium, iron, zinc, manganese, copper, and sodium often exceeding daily requirements in moderate servings; for instance, samples analyzed for human nutrition qualify as rich sources of copper (up to 5–10 mg/100g), iron (10–50 mg/100g), magnesium (100–300 mg/100g), manganese (5–20 mg/100g), and phosphorus (200–500 mg/100g).^[95] ^[93] Bioactive compounds, including flavonoids (e.g., quercetin, kaempferol), phenolic acids, and carotenoids, contribute antioxidant capacity, though levels fluctuate widely (e.g., total phenolics 1–20 mg/g).^[94] Evidence-based uses of bee pollen center on its role as a dietary supplement to augment nutrient intake, particularly proteins, vitamins, and minerals in populations with deficiencies, such as athletes or those with malnutrition, due to its provision of bioavailable essentials akin to a "complete food."^[93] ^[96] Human clinical trials remain sparse and small-scale; for example, randomized studies on allergic rhinitis (n=20–50) indicate modest symptom reduction via oral administration (e.g., 500 mg/day for 4–12 weeks), attributed to immunomodulatory effects from pollen proteins and phenolics, though placebo-controlled efficacy is inconsistent and requires replication.^[97] Limited trials for benign prostatic hyperplasia (n=30–60) report urinary symptom improvements with 1–3 g/day over 3–6 months, potentially linked to anti-inflammatory bioactives, but without robust controls or long-term data.^[97] Broader claims for antioxidant, anti-inflammatory, or metabolic benefits (e.g., lipid metabolism enhancement via phenolics) derive mainly from in vitro assays and rodent models, lacking confirmatory large-scale human RCTs; thus, while nutrient supplementation is supported, therapeutic applications beyond general nutrition await stronger evidence.^[92] ^[98]

Management Strategies for Allergies

Allergen avoidance forms the foundational strategy for managing pollen-induced allergic rhinitis, though complete elimination of exposure proves challenging due to airborne dispersal. Effective measures include monitoring daily pollen forecasts via meteorological services and restricting outdoor activities during high-count periods, typically mornings and windy days; keeping windows and doors closed while using air-conditioned environments with high-efficiency particulate air (HEPA) filters; and post-exposure routines such as showering, washing hair, and changing clothes to dislodge adhered pollen grains.^[99] These interventions reduce symptom severity by limiting inhalation, with pollen forecasts aiding proactive planning, yet evidence from scoping reviews indicates variable individual efficacy influenced by local pollen loads and adherence.^[100] Additional tactics encompass wearing wraparound sunglasses to shield ocular exposure and employing nasal irrigation with saline to flush allergens from nasal passages, which provides adjunctive symptom relief without pharmacological risks.^[101] Pharmacological treatments target symptom control, with intranasal corticosteroids (INCS) endorsed as first-line therapy for persistent or moderate-to-severe seasonal allergic rhinitis due to their potent anti-inflammatory effects on nasal mucosa. Meta-analyses of randomized trials demonstrate INCS, such as fluticasone furoate, outperform placebo and oral antihistamines in reducing total nasal symptom scores by 20-30% and improving quality of life, with onset within 12-24 hours and peak efficacy by day 7.^[102]^[103] Second-generation oral antihistamines (e.g., cetirizine, loratadine) suit mild intermittent symptoms, alleviating sneezing and pruritus but less effectively addressing congestion compared to INCS; intranasal antihistamines like azelastine offer faster relief for acute episodes.^[104] Combination products, such as azelastine-fluticasone, yield synergistic benefits, ranking highest in network meta-analyses for overall symptom control across nasal and ocular domains with minimal systemic absorption.^[102] Leukotriene receptor antagonists (e.g., montelukast) provide modest adjunctive value in polysensitized patients but lack superiority over INCS monotherapy.^[105] Allergen immunotherapy (AIT) represents a disease-modifying approach, inducing immune tolerance to specific pollen allergens like grass or ragweed via subcutaneous injections (SCIT) or sublingual tablets/drops (SLIT). Systematic reviews and meta-analyses of randomized controlled trials confirm AIT reduces seasonal symptom scores by 30-40% and medication requirements, with sustained effects persisting 2-3 years post-treatment; SLIT for grass pollen achieves comparable efficacy to SCIT in adults and children, though SCIT may edge out in severe cases.^[106]^[107] Real-world data from registries spanning 18 years show pollen AIT lowers allergic rhinitis exacerbation risks and healthcare utilization, particularly when initiated pre-seasonally.^[108] Safety profiles favor SLIT with fewer anaphylactic events than SCIT, though both require specialist oversight; efficacy hinges on standardized extracts matching regional allergens, with non-response rates around 20% linked to adherence or polysensitization.^[109] Guidelines recommend AIT for patients unresponsive to pharmacotherapy or seeking long-term remission, prioritizing it over indefinite symptomatic management.^[110]

Applications and Analysis

Forensic Palynology

Forensic palynology employs the microscopic examination of pollen grains and spores to link individuals, objects, or locations in criminal and civil investigations, leveraging the unique assemblages of pollen types that reflect specific geographic areas, vegetation, and seasonal conditions.^[111] These microfossils, highly resistant to degradation—even surviving temperatures up to 700°C for short durations—can transfer via clothing, vehicles, footwear, or soil, persisting as trace evidence long after an event.^[111] Traditional identification relies on morphological features observed through transmitted-light microscopy or scanning electron microscopy, while modern approaches incorporate DNA barcoding using markers such as rbcL and matK to achieve species-level precision, supplemented by high-throughput sequencing for complex mixtures.^[111] The discipline traces its forensic origins to the 1950s, with an early landmark case in Austria where fossilized pollen, approximately 20 million years old, recovered from a suspect's boots matched sediments from a murder site along the Danube River, establishing the perpetrator's presence at the scene.^[112] Collection methods include vacuum sampling from fabrics or surfaces, tape adhesion for surface traces, and chemical extraction from soils or sediments, often requiring controlled processing to avoid contamination, as pollen viability depends on timely analysis before environmental dispersal alters profiles.^[111] In practice, pollen evidence has proven instrumental in verifying alibis, tracing movement histories over distances up to 150 miles, and corroborating timelines, as seen in a U.S. murder investigation where regional pollen signatures refuted a suspect's claimed itinerary.^[111] Notable applications include the 2015 identification of "Baby Doe," an unidentified child found on Deer Island in Boston Harbor; pollen from her hair and clothing, analyzed via vacuum extraction and microscopic comparison, revealed local northeastern U.S. flora indicative of the Boston area, narrowing the search and leading to her confirmation as Bella Bond, with subsequent charges against her mother and her mother's boyfriend for murder.^[113] Similarly, in a 2015 New York cold case involving Tammy Jo Alexander's remains in a cornfield, pollen profiling matched site-specific assemblages to evidence on associated items, aiding victim linkage.^[111] These cases underscore pollen's role as a "silent witness," providing probabilistic associations rather than absolute proof, often integrated with other forensic data like DNA or ballistics. Despite its evidentiary value, forensic palynology faces constraints, including the limited number of qualified practitioners—particularly in regions like the United States—and incomplete reference databases for pollen morphology and genetics, which can hinder precise sourcing in urban or cosmopolitan settings where pollen mixes homogenize.^[111] Ubiquity of certain taxa, seasonal variability, and potential secondary transfer further necessitate cautious interpretation, with pollen evidence rarely standing alone but serving to support or challenge narratives when corroborated.^[112] Advances in automated imaging and molecular tools continue to expand its reliability, though judicial acceptance varies, emphasizing the need for standardized protocols to elevate its courtroom utility.^[111]

Microscopy, Staining, and Molecular Techniques

Pollen grains are routinely analyzed using light microscopy (LM) to determine morphological features including size, shape, aperture configuration, and exine ornamentation, which are critical for taxonomic classification in palynology.^[114] Scanning electron microscopy (SEM) enhances resolution of surface microstructures, such as tectal patterns and sculpturing, by producing three-dimensional images at magnifications up to 10,000x, often after critical point drying or sputter coating to prevent charging.^[115] Transmission electron microscopy (TEM) elucidates ultrastructural details, including the layered exine composition of sporopollenin and internal elements like the vegetative and generative nuclei.^[114] These techniques collectively enable precise differentiation of pollen taxa, with LM sufficient for routine identification and electron microscopy reserved for ambiguous or fossil specimens.^[116] Staining protocols facilitate viability assessment and structural visualization under microscopy. Acetocarmine dye penetrates viable pollen grains, staining chromatin red to indicate fertile cytoplasm and nuclear integrity, commonly applied by heating pollen in a 1-2% solution for 5-10 minutes.^[117] Fluorescein diacetate (FDA) evaluates membrane integrity, hydrolyzing to fluorescent fluorescein in enzymatically active live cells under UV excitation, with viability quantified by fluorescence intensity.^[118] Alexander's stain differentiates viable (pink-purple) from non-viable (green) grains by differential dye uptake, offering rapid screening in crops like faba beans where viability correlates with germination rates exceeding 80% in stained samples.^[119] These methods, while empirical, can overestimate viability compared to in vitro germination tests due to latent dormancy effects.^[120] Molecular techniques, particularly DNA metabarcoding, surpass morphological limits by extracting and sequencing genetic markers from pollen for species-level resolution. Protocols involve lysis of pollen walls with CTAB-based buffers, followed by PCR amplification of barcoding loci such as rbcL, matK, or ITS regions, and high-throughput sequencing via Illumina or nanopore platforms.^[121] This approach identifies pollen in mixed samples, such as bee forage or honey, with detection thresholds as low as 1% relative abundance, enabling ecological tracing without intact morphology.^[122] In forensic palynology, metabarcoding reconstructs crime scene plant assemblages from trace pollen, offering probabilistic linkage via haplotype matching against databases like GenBank.^[123] Limitations include DNA degradation in aged pollen and primer biases favoring certain taxa, necessitating multi-locus strategies for accuracy above 90% in controlled studies.^[124]

Contemporary Research and Debates

Trends in Pollen Seasons and Climate Data

In North America, pollen seasons have lengthened by an average of 20 days from 1990 to 2018, accompanied by a 21% increase in total pollen concentrations, based on analysis of data from 60 pollen-monitoring stations across the continent.^[125] These changes correlate with regional warming trends, including earlier spring onsets that advance pollen release by trees and extended autumn periods that prolong herbaceous pollen emission.^[125] In Europe, long-term monitoring from 1990 onward shows similar advances in pollen season starts, with birch (Betula) seasons beginning up to 10-15 days earlier in northern regions, driven by temperature increases of 1-2°C over the period.^[126] 30015-4/fulltext) Elevated atmospheric CO2 concentrations, which have risen from approximately 350 ppm in 1990 to over 400 ppm by 2020, enhance pollen production in many plant species through fertilization effects, leading to larger pollen grains and higher yields per plant; experimental studies confirm up to 40% increases in pollen output under doubled CO2 levels.^[127] Warmer temperatures further amplify this by extending the growing season, with models indicating that a 1°C rise can shift pollen peaks earlier by 3-5 days and boost annual emissions by 16-40% in temperate zones.^[69] Precipitation variability modulates these effects, with drier conditions in some regions intensifying pollen release by reducing grain hydration and dispersal barriers.^[69] For ragweed (Ambrosia), a key allergen, U.S. data from 1995-2012 reveal season extensions of 11-27 days linked to advanced fall frosts and higher CO2-driven biomass.^[74] Projections under moderate warming scenarios (RCP4.5) forecast additional pollen season extensions of 10-40 days by mid-century in North America and Europe, with total emissions rising 10-50% depending on species and location, though these estimates vary due to uncertainties in plant adaptation and extreme weather feedbacks.^[69] Empirical data from urban vs. rural sites suggest localized factors like heat islands exacerbate trends, but continent-wide patterns align with global temperature records rather than land-use changes alone.^[125] A 2024 meta-analysis of 50+ studies confirms positive correlations between warming and annual pollen integrals (APIn), though effect sizes differ by taxon, with grasses showing less sensitivity than trees.^[90]

Controversies in Allergy Causation and Botanical Practices

The preferential planting of male dioecious trees in urban landscaping, a practice dubbed "botanical sexism," has sparked debate over its contribution to heightened pollen exposure and allergy prevalence. City planners historically favored male trees to avoid the mess of fruit and seeds from females, resulting in skewed sex ratios—such as 80-90% male ginkgos in some U.S. cities—leading to concentrated pollen release without natural fertilization limits.^[128] ^[129] However, empirical assessments challenge the notion that this alone drives allergy epidemics, as historical pollen records show no explosive urban increases commensurate with claims, and rising sensitization rates correlate more strongly with prolonged seasons and population density than tree gender imbalances.^[130] ^[131] Scientific modeling of urban forests indicates wide variability in allergenic risk from tree selections, with exposure estimates for high-allergen species ranging from 1% to 74% across cities due to inconsistent use of low-pollen alternatives like monoecious maples or sterile cultivars.^[132] In New York City, for instance, post-1930s plantings amplified certain pollens but were offset by overall canopy declines, suggesting that targeted removal or replacement of species like ailanthus (up to 25% of urban pollen in some areas) could reduce loads by 20-50% without broad gender shifts.^[133] Critics of expansive "allergy-friendly" guidelines argue they overlook ecological trade-offs, such as reduced biodiversity from excluding native dioecious species, potentially exacerbating monoculture vulnerabilities.^[134] ^[135] Debates on allergy causation extend to air pollution's role, where oxidants like ozone fragment pollen into submicronic allergenic particles (1-2.5 μm) that bypass nasal filters and trigger deeper respiratory inflammation, as observed in birch pollen studies showing 10-fold IgE response increases under polluted conditions.^[136] ^[137] Fossil fuel emissions, including diesel particulates with adjuvants like PAHs, enhance pollen protein allergenicity by up to 200% in vitro, fueling arguments that anthropogenic pollution—not pollen volume alone—causally drives the 50% global allergy rise since 1990.^[138] Yet, causal attribution remains contested, with longitudinal data indicating pollution amplifies symptoms in sensitized individuals but does not initiate atopy, as rural cohorts in low-pollution zones exhibit similar pollen-specific IgE rates when accounting for genetic and exposure factors.^[139] Elevated CO2 levels, experimentally boosting ragweed pollen allergens by 60-90% at 370-550 ppm, intersect these claims, though field validations are limited by confounding climate variables.^[140]

References

[1]
[PDF] What is pollen? - The University of Western Australia
Pollen is essential for sexual reproduction of flowering plants and plants that produce cones. Each pollen grain contains male gametes necessary for ...
[2]
Pollen allergic disease: pollens and its major allergens - PMC - NIH
The pollen grain is part of the flowering plant life cycle, and is a specialized structure that harbors the flowering plant male gametes. Its biological ...<|separator|>
[3]
Structure of Pollen grains - BYJU'S
Dec 10, 2022 · Pollen grains are microscopic structures, which bear androecium – a male reproductive organ of a flower. The interior section of pollen grain ...
[4]
Pollen Grains: Definition, Structure, and Diagram - Biology - Vedantu
Rating 4.2 (373,000) The main function of pollen grains is to transfer male genetic material for fertilization during sexual reproduction in plants. Key points: They deliver male ...
[5]
Pollination - The Australian Museum
As a result of pollination the plants produce seeds. Pollen can be dispersed by wind, water and animal pollinators such as insects, bats and birds. How ...How Important Is Insect... · How Do Insects Pollinate... · How Do Plants Attract...
[6]
Pollen Allergy: Causes, Symptoms & Treatment - Cleveland Clinic
A pollen allergy causes symptoms like stuffy nose and coughing when a person breathes in pollen, a particle produced by certain plants, trees and grasses.
[7]
Pollen and Your Health | Climate and Health - CDC
Mar 2, 2024 · Health impact. If you have hay fever, also known as "allergic rhinitis," breathing in pollen can cause: sneezing. congestion. runny nose. Pollen ...
[8]
Pollen Seasons Are Longer and More Intense, Affecting Millions
Mar 18, 2025 · Pollen allergies are very common and trigger allergic rhinitis and asthma symptoms. With over 100 million people affected by allergies and/or ...Missing: humans | Show results with:humans
[9]
How Do Pollen Allergens Sensitize? - PMC - NIH
Plant pollen is one of the main sources of allergens causing allergic diseases such as allergic rhinitis and asthma. Several allergens in plant pollen are ...
[10]
Pollen grain - (General Biology I) - Vocab, Definition, Explanations
A pollen grain is a microscopic structure produced by seed plants that contains the male gametes for fertilization.
[11]
The molecular structure of plant sporopollenin - PubMed
Sporopollenin is a ubiquitous and extremely chemically inert biopolymer that constitutes the outer wall of all land-plant spores and pollen grains1.
[12]
Pollen Wall and Sporopollenin - ScienceDirect.com
The pollen wall, the sporoderm, is the most complex wall system in higher plants. The exine, composed of sporopollenin, is the outer, resistant layer.
[13]
ENY152/IN868: The Benefits of Pollen to Honey Bees
Pollen, in the form of bee bread, is the honey bee's main source of protein and it also provides fats/lipids, minerals, and vitamins.
[14]
Bee Pollen: Chemical Composition and Therapeutic Application - PMC
Bee pollen is a raw material from which bees produce bee bread. They collect pollen from plant anthers, mix it with a small dose of the secretion from salivary ...<|separator|>
[15]
[PDF] Microsporogenesis and Microgametogenesis in Plants
Microspores i.e., the pollen grains, are developed inside microsporangia. The microsporangia are developed inside the corners of the 4-lobed anther.
[16]
Microsporogenesis: Process, Stages, and Significance
Jan 19, 2025 · The process of formation of microspores or pollen grains inside the pollen sac or microsporangium is called microsporogenesis.
[17]
Microsporogenesis, microgametogenesis, and pollen grain ...
Tapetum plays a main role in the development of the pollen grains, and some of its main functions are the production and release of callase enzyme, the ...
[18]
Male gametogenesis in flowering plants - Frontiers
Jan 4, 2024 · Microsporogenesis is the differentiation and development of archesporial cells into microsporocytes. Subsequently, meiosis occurs, and the ...
[19]
Pollen Development | SpringerLink
Oct 10, 2018 · The development of a pollen grain includes microsporogenesis and microgametogenesis (Figs. 1 and 2, Gomez et al. 2015; Keijzer and Willemse 1988).
[20]
Molecular genetic analyses of microsporogenesis and ... - PubMed
Within the anther, male meiosis produces microspores, which further develop into pollen grains, relying on both sporophytic and gametophytic gene functions.
[21]
From birth to function: Male gametophyte development in flowering ...
In flowering plants, a diploid pollen mother cell undergoes meiosis to produce a tetrad of haploid microspores, a process called microsporogenesis. Each ...
[22]
[PDF] Anther Development: Basic Principles and Pract ical Applicat ions
During phase 2, pollen grains differentiate, the an- ther enlarges and is pushed upward in the flower by filament extension, and tissue degeneration, dehiscence ...
[23]
[PDF] Exine and Aperture Patterns on the Pollen Surface
The pollen coat is a sticky, oily substance made of lipids, proteins, aromatic compounds, and pigments (Pacini and Hesse, 2005; Rejón et al., 2016). Neither ...<|control11|><|separator|>
[24]
[PDF] Pollen structure and morphology - Termedia
Pollen structure includes shape, size, exine sculpturing, and apertures (pores or furrows). The exine is outer, and intine is inner layer. Key features are ...
[25]
Sequential Deposition and Remodeling of Cell Wall Polymers ...
Jul 26, 2021 · The mature pollen wall can be broadly divided into two layers, an outer sporopollenin-rich exine and an inner intine, which has a composition ...
[26]
Shape, Color and Size
Aug 22, 2012 · Pollen grains of various species can vary quite a lot in size (from about 10 to nearly 100 micrometer; exceptions are the thread-shaped pollen grains of some ...Missing: variations | Show results with:variations
[27]
Pollen morphological variability correlates with a large-scale ... - WE
May 12, 2020 · A total of 10 pollen grain shapes were quantified and discussed following their specific occurrences within different climatic zones. Occurrence ...
[28]
Types of Apertures
Pollen grains with pores are porate and those with colpi are colpate. If both pore and colpus are combined in the same aperture, the pollen grain is colporate.
[29]
Does climate affect pollen morphology? Optimal size and shape of ...
Oct 31, 2011 · We report that pollen grains under more intense desiccation stress during flowering periods tend to be larger but do not change shape.
[30]
[PDF] How many flowering plants are pollinated by animals?
The mean proportion of animal-pollinated plants increases from 78% of species in temperate-zone communities, to. 94% in tropical communities (Fig. 1). This ...
[31]
Wind of change: new insights on the ecology and evolution of ... - NIH
Wind pollination has evolved at least 65 times from animal-pollinated ancestors, and approx. 10 % of angiosperm species rely on wind pollination (Linder, 1998; ...
[32]
Microscopy Research and Technique - Analytical Science Journals
Nov 2, 2021 · We found that anemophilous pollen grains are small, spheroidal, or oblate spheroidal, while entomophilous pollen grains are medium and oblate.
[33]
Morphological differences between anemophilous and ... - PubMed
We found that anemophilous pollen grains are small, spheroidal, or oblate spheroidal, while entomophilous pollen grains are medium and oblate.Missing: peer | Show results with:peer
[34]
Insect pollination for most of angiosperm evolutionary history
Jun 5, 2023 · Both gymnosperms and angiosperms depend on pollination to reproduce sexually, with pollen transfer effected by insects, vertebrates, wind or ...
[35]
Ultramicroscopic Characterization of Mature Pollen Grains of ...
Entomophilous pollen grains usually store more lipids than starch as flowers open, whereas anemophilous pollen grains tend to accumulate more starch grains ...
[36]
Pollen Tube Navigation from Germination to Fertilization
Apr 29, 2019 · In flowering plants, pollen tubes undergo tip growth to deliver two nonmotile sperm to the ovule where they fuse with an egg and central cell to ...
[37]
Mechanics of Pollen Tube Elongation: A Perspective - Frontiers
Pollen tube (PT) serves as a vehicle that delivers male gametes (sperm cells) to a female gametophyte during double fertilization, which eventually leads to ...Membrane Dynamics... · Pollen Tube Elongation... · How Do Pollen Tubes Sense...
[38]
The quest for the central players governing pollen tube growth and ...
Pollen tube growth results from the dynamic formation of actin cables along which secretory vesicles move to provide new material to the tip. Changes in H+ and ...
[39]
Chemical signaling for pollen tube guidance at a glance
Jan 29, 2018 · Several mechanisms have been proposed to explain the precise growth of pollen tubes towards the ovules. These include mechanical, chemotropic, ...Introduction · One-to-one pollen tube guidance · Multistep control of pollen tube...
[40]
Deep imaging reveals dynamics and signaling in one-to-one pollen ...
May 21, 2024 · After the pollen tube enters the transmitting tract (TT) within the ovary, it reaches the ovule via three steps: emergence from the TT, growth ...Results · Methods · Pollen Tube Growth Rate And...
[41]
Tracking pollen tube and ovule development in vivo reveals rapid ...
Jan 20, 2025 · We demonstrate that the development of pollen tubes from germination to fertilization is rapid, within just 4 h. On fertilization, fertilized ...
[42]
Fertilization Mechanisms in Flowering Plants - PMC - PubMed Central
It has been reported recently that the pollen tube is capable of carrying a virus towards the embryo sac during fertilization [38], but it is unlikely that ...
[43]
Further study of Late Devonian seed plant Cosmosperma polyloba
Jun 26, 2017 · Among them, Cosmosperma polyloba represents the first Devonian ovules known from China and East Asia that are associated with pollen organs and ...
[44]
Pollen Organ Telangiopsis sp. of Late Devonian Seed Plant and ...
Jan 25, 2016 · Comparisons among Late Devonian seed plants recognize several branching patterns in the fertile fronds/axes bearing terminal pollen organs.
[45]
Evolution of development of pollen performance - PubMed
With the origin of pollination in ancient seed plants, the male gametophyte ("pollen") began to evolve a new and unique life history stage, the progamic ...
[46]
Evolution: Pollen or Pollinators — Which Came First? - ScienceDirect
Apr 22, 2013 · The bee fossil record is relatively poor but indicates that they might have arisen in the mid-Cretaceous, roughly 140–110 million years ago (Mya) ...
[47]
The evolution of pollen germination timing in flowering plants
The pollination to fertilization process (progamic phase) is thought to have become greatly abbreviated with the origin of flowering plants. In order to ...<|separator|>
[48]
The Ecology and Evolution of Pollen Performance
Mar 15, 2016 · Pollen grains encompass tiny plants (male gametophytes) that develop and produce sperm cells. After the discovery of double fertilization in flowering plants.
[49]
Fossil Pollen - Illinois State Museum
Oct 21, 2003 · Pollen preserves best if the sedimentary environment lacks oxygen or is acidic, conditions unfavorable for the organisms that decompose pollen.Missing: paleopalynology | Show results with:paleopalynology
[50]
Paleobotany + Palynology - Florida Museum of Natural History
Jan 18, 2022 · Palynology is the study of plant pollen, spores and certain microscopic plankton organisms (collectively termed palynomorphs) in both living and fossil form.
[51]
[PDF] POLLEN PRODUCTION, TRANSPORT AND PRESERVATION
May 3, 1981 · Fossil pollen used in early studies of paleoecology was usually obtained from lacustrine sediments because of excellent preservation of pollen ...Missing: paleopalynology | Show results with:paleopalynology
[52]
Seed plants: Fossil Record
By the end of the Devonian, a variety of early seed plants collectively known as "lyginopterids" appeared. These include Sphenopteris, a plant with fern-like ...
[53]
A Late Devonian Fertile Organ with Seed Plant Affinities from China
May 29, 2015 · The earliest pollen organs occur in the Late Devonian (Famennian, 372-359 million years ago) but are extremely rare and typically too ...
[54]
Late Devonian–Early Carboniferous palynology of the CSDP-2 ...
Late Devonian–Early Carboniferous spores recovered from the depths of 2140 m to 2031.3 m in the CSDP-2 Borehole in the southern Yellow Sea are systematically ...
[55]
Angiosperm-like pollen and Afropollis from the Middle Triassic ...
Oct 1, 2013 · The first known fossil angiosperm pollen grains as well as those of the most basal living species are described as columellate and monosulcate.
[56]
Eocene fossil is earliest evidence of flower-visiting by birds - Journals
May 1, 2014 · We report a bird skeleton from the Middle Eocene (47 Ma) of Messel in Germany with preserved stomach contents containing numerous pollen grains.
[57]
UV-B radiation was the Devonian-Carboniferous boundary ...
May 27, 2020 · Regarding pollen and spores, the terrestrial extinction is clearly expressed as the complete loss of diversity (6, 7) across the Devonian- ...
[58]
Ancient pollen reveals stories about Earth's history, from the asteroid ...
May 20, 2025 · Among the rocks and marine fossils, scientists have found fossilized pollen from the Late Cretaceous and Early Paleocene periods that reflects ...
[59]
The evolutionary history evident in grass pollen morphology
Jan 9, 2025 · All grass species produce pollen that is simple, psilate, and spherical, with only small differences in the surface patterning and thickness of the pollen ...
[60]
Palaeoecological evidence of pollen morphological changes
Sep 1, 2022 · Pollen grains have morphological features that allow for the identification of different species, genera, and families of flowering plants.
[61]
Honey Bees Prefer Pollen Substitutes Rich in Protein Content ...
Feb 28, 2023 · Pollens being the primary source of protein, lipids, vitamins, and minerals are vital for bee development and reproduction.
[62]
Honey bee foraged pollen reveals temporal changes in pollen ...
Dec 1, 2021 · Pollen from flowers is the only natural source of protein for bees, and pollens can range widely in protein content from 2.5% to 61% (Buchmann, ...
[63]
Plants, pollinators and their interactions under global ecological ...
Pollen is a powerful biomarker for detecting spatial and temporal variation in plant and pollinator species assemblages and interactions, making it ideal for ...
[64]
Pollen dispersal slows geographical range shift and accelerates ...
Sep 12, 2016 · Pollen dispersal slows the range shift in space but facilitates the evolution of new climatic niche limits, such that the species becomes adapted to warmer ...
[65]
Pollinator diversity benefits natural and agricultural ecosystems ...
Feb 3, 2022 · Research indicates that in natural ecosystems, pollinator diversity enhances pollination during environmental and climatic perturbations, thus alleviating ...
[66]
[PDF] a specialist bee pollinates more florets but does not move pollen ...
Nov 11, 2019 · We examined two aspects of pollinator effectiveness—effective pollen deposition and effective pollen movement—for insects visiting Echinacea ...
[67]
Persistence of Plants and Pollinators in the Face of Habitat Loss
Habitat loss negatively affects pollinator diversity and the pollination service provided by insects, a key ecosystem service supporting the quantity, quality ...
[68]
Pollination and seed dispersal are the most threatened processes of ...
Jul 20, 2016 · These included land-use changes such as fragmentation, selective logging and conversion to secondary forest habitat, as well as defaunation such ...
[69]
Projected climate-driven changes in pollen emission season length ...
Mar 15, 2022 · Pollen emissions from anemophilous vegetation are directly correlated with meteorological conditions, such as temperature and precipitation.
[70]
Heatwaves exacerbate pollen limitation through reductions in pollen ...
Our results suggest flowers that develop during heatwaves are likely to experience exacerbated pollen quantity and quality limitation.
[71]
Impact of moderate temperature on pollen development in maize
Apr 9, 2024 · Exposure to high temperatures during the plant reproductive phase can lead to a dramatic decrease in seed production, largely through abnormal pollen ...
[72]
[PDF] Rising CO2 and pollen production of common ragweed (Ambrosia ...
Although environmental factors such as precipitation and temperature are recognized as influencing pollen production, the impact of rising atmospheric ...
[73]
Elevated atmospheric CO2 has small, species-specific effects on ...
Jun 14, 2024 · Our results indicate that future eCO 2 is unlikely to uniformly change pollen chemistry or plant growth across flowering species.
[74]
Climate Change Indicators: Ragweed Pollen Season | US EPA
Sep 11, 2025 · Warmer temperatures and increased carbon dioxide concentrations also lead ragweed and other plants to produce more pollen, and the pollen they ...
[75]
Effects of Drought Stress on Pollen Sterility, Grain Yield, Abscisic ...
Drought stress induced pollen sterility is a detrimental factor reducing grain number in wheat. Exploring the mechanisms underlying pollen fertility under ...
[76]
Drought and temperature stresses impact pollen production and ...
Jul 19, 2023 · Plants grown under temperature and water stresses were shorter and had fewer leaves at flowering than control plants.INTRODUCTION · MATERIALS AND METHODS · RESULTS · DISCUSSION
[77]
Revisiting light pollution effects on photoperiodic growth in short-day ...
With HPS lighting, higher LP significantly increased the period of stem elongation and delayed plant flowering, maturity, and harvest, which increased the risk ...
[78]
[PDF] effect of photoperiod treatments on pollen viability and flowering at ...
Analysis over a five-year period showed that genotypes from the photoperiod house produced significantly (P<0.001) more fertile pollen than genotypes from the.
[79]
Effector mechanisms in allergic reactions - Immunobiology - NCBI
Allergic reactions are triggered when allergens cross-link preformed IgE bound to the high-affinity receptor FcεRI on mast cells.
[80]
Innate responses to pollen allergens - PMC - NIH
Pollens have aqueous pollen extract proteins, proteases, lipids, and NADPH oxidases that stimulate innate immune responses. These innate immune responses ...
[81]
Tree pollen allergens—an update from a molecular perspective - PMC
Tree pollen allergies are mainly elicited by allergenic trees belonging to the orders Fagales, Lamiales, Proteales, and Pinales.
[82]
Pollen Allergens for Molecular Diagnosis - PMC - PubMed Central
Mar 22, 2016 · Here, the most important species triggering pollen allergy are Bermuda grass, Bahia grass, and Johnson grass [20]. Pollination of these grasses ...
[83]
How Do Pollen Allergens Sensitize? - Frontiers
Plant allergens from tree, grass and weed pollen belong to diverse protein classes the most significant of which are Bet v 1 homologs, lipid transfer proteins ...
[84]
Allergic rhinitis: Clinical manifestations, epidemiology, pathogenesis ...
Allergic rhinitis is a common condition affecting 10 to 30 percent of children and adults in the United States and other resource-abundant countries [5-10]. It ...<|separator|>
[85]
Facts and Stats - 50 Million Americans Have Allergies | ACAAI Patient
27.2% of children show allergy symptoms, and 31.8% of adults, which tallies to over 100 million people.2; Allergic rhinitis, often called hay fever, is a common ...Missing: epidemiology | Show results with:epidemiology
[86]
FastStats - Allergies and Hay Fever - CDC
Allergies · Percent with any allergy: 31.8% · Percent with seasonal allergy: 25.7% · Percent with eczema: 7.3% · Percent with food allergy: 6.2%.Missing: 2020-2025 | Show results with:2020-2025
[87]
Immunological Mechanisms in Allergic Diseases and Allergen ...
The key cytokines responsible for the allergic response include interleukin- (IL-) 4, IL-5, and IL-13, as well as innate lymphoid (ILC-2) cells which may ...
[88]
Mechanisms of allergen-specific immunotherapy and immune ...
In pollen-sensitive patients, desensitization prevents elevation of the serum specific IgE during the pollen season [170]. The changes in IgE levels cannot ...
[89]
Mechanism of action of allergen immunotherapy - PubMed
Sep 1, 2016 · Allergen immunotherapy (AIT) leads to the production of antiallergen immunoglobulin (IgG) or blocking antibody in the serum and an increase in antiallergen IgG ...
[90]
Review Impacts of climate change on allergenic pollen production
Apr 15, 2024 · A higher temperature, coupled with an increase in carbon dioxide concentration in the air, adversely affects plant growth and results in more ...
[91]
Composition and functionality of bee pollen: A review - ScienceDirect
Bee pollen contains carbohydrates (13–55%), proteins (10–40%), lipids (1–13%), crude fibre (0.3–20%) and ash content (2–6%) (Campos et al., 2008). In addition, ...
[92]
Bee Pollen: Current Status and Therapeutic Potential - PMC - NIH
May 31, 2021 · The latest evidence has shown that phenolic compounds can enhance the absorption of nutrients, lipid metabolism, and weight loss [37]. Bee ...
[93]
Bee pollen as a food and feed supplement and a therapeutic remedy
BP is rich in protein, fat, and minerals (particularly Ca, Mg, Fe, and P) and gives a nutritional value to pollen similar to or greater than dry legumes and is ...Abstract · Composition and morphology... · Factors affecting bee pollen · Apitherapy
[94]
Bee Pollen as Functional Food: Insights into Its Composition and ...
Bee pollen, also called bee-collected pollen, contains a wide range of nutritious elements, including proteins, carbs, lipids, and dietary fibers.3. Bee Pollen: From Flowers... · 4. Chemical Composition · 4.2. Micronutrients
[95]
Mineral composition of bee pollen and its relationship with botanical ...
Regarding the nutritional value for humans, bee pollen samples could be considered as a food rich in copper, iron, magnesium, manganese, and phosphorus. Finally ...
[96]
Translational Research on Bee Pollen as a Source of Nutrients - MDPI
The promising uses of bee pollen for malnutrition, digestive health, metabolic disorders, and other bioactivities which could be helpful to readjust homeostasis ...
[97]
Bee Pollen: Clinical Trials and Patent Applications - PMC - NIH
In particular, bee pollen has been applied in clinical trials for allergies and prostate illnesses, with a few investigations on cancer and skin problems.
[98]
Are There Benefits of Bee Pollen? - Cleveland Clinic Health Essentials
Oct 3, 2024 · Studies on the potential benefits of bee pollen have been small, and most of them haven't been done on humans, which means that these benefits ...
[99]
Nonpharmacological measures to prevent allergic symptoms in ...
Dec 1, 2021 · Pollen forecasts can be a valuable tool for pollen avoidance as well as management of pollen allergies [38, 57]. They are mainly used during ...
[100]
Avoidance Measures for Patients with Allergic Rhinitis: A Scoping ...
Feb 3, 2023 · In this scoping review, our objective is to identify measures of allergen avoidance and to evaluate their effectiveness in the management of AR.
[101]
Allergic rhinitis | Allergy, Asthma & Clinical Immunology | Full Text
Dec 27, 2024 · Therapeutic options available to achieve this goal include avoidance measures, nasal saline irrigation, oral antihistamines, intranasal ...
[102]
Efficacy and safety of intranasal medications for allergic rhinitis ...
Nov 16, 2024 · Among individual medications, azelastine-fluticasone, and fluticasone furoate were the most frequently highest-ranked interventions for efficacy ...
[103]
Intranasal antihistamines and corticosteroids in allergic rhinitis
Apr 26, 2024 · Antihistamines and intranasal corticosteroids are the main pharmacological treatment approaches for allergic rhinitis (AR). The 2020 Allergic ...
[104]
Intranasal Versus Oral Treatments for Allergic Rhinitis - PubMed
Sep 7, 2024 · Conclusions: Randomized controlled trials suggest that intranasal treatments are more effective than oral treatments at improving symptoms and ...
[105]
Current treatment strategies for seasonal allergic rhinitis - NIH
Aug 10, 2022 · The treatment approach for AR may be based on drugs aimed at repealing or reducing allergic symptoms or on allergen immunotherapy (AIT), which ...
[106]
Efficacy of different allergen-specific immunotherapies for ... - Frontiers
Sep 24, 2025 · In conclusion, both SLIT and SCIT are effective treatments for AR, showing significant efficacy in adults, children, and for various allergens.
[107]
Efficacy of Grass Pollen Allergen Sublingual Immunotherapy Tablets ...
This computerized bibliographic search assesses the efficacy and safety of the sublingual tablets licensed as drugs in the treatment of patients with.
[108]
The effectiveness of pollen allergen immunotherapy on allergic ...
Jan 21, 2024 · This analysis of Danish national prescription data over 18 years shows that pollen allergen immunotherapy reduces allergic rhinitis (AR) ...
[109]
Allergen immunotherapy: past, present and future - Nature
Oct 17, 2022 · Systematic reviews and meta-analyses have confirmed efficacy of pre-seasonal or co-seasonal immunotherapy for seasonal rhinitis and continuous ...<|control11|><|separator|>
[110]
[PDF] Rhinitis 2020: A practice parameter update
Treatment of seasonal allergic rhinitis: an evidence-based focused 2017 guideline ... lingual immunotherapy with grass allergens for seasonal allergic rhinitis ...
[111]
Pollen molecular biology: Applications in the forensic palynology ...
Mar 4, 2020 · Pollen grains may remain preserved for many years (Walsh and Horrocks, 2008). On the other hand, this field has disadvantages because it lacks ...
[112]
The Use of Forensic Palynology in Solving Crimes - AZoLifeSciences
Aug 6, 2024 · Palynology, the study of pollen and spores, is utilized in forensic science to examine evidence linked to crime scenes.The Use Of Forensic... · The Power Of Pollen And... · Analyzing Pollen EvidenceMissing: definition | Show results with:definition<|separator|>
[113]
Pollen Analysis Helps Identify Victim in Baby Doe Case - LSU
To help investigators identify Bella, DHS palynologists combed through her hair and clothes for remnants of pollen and other forensic evidence that could be ...
[114]
Identification of pollen taxa by different microscopy techniques - PMC
Sep 1, 2021 · Pollen identification uses light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Phase ...One-Dimensional Description · Fig 3. Typical Exine... · Fig 4. Scree Plots Of Factor...Missing: peer- | Show results with:peer-
[115]
A Simple and User-Friendly Method for High-Quality Preparation of ...
Aug 1, 2024 · Scanning electron microscopy (SEM) produces detailed magnified images of the pollen grains by scanning their surface. Commonly, SEM analysis of ...Missing: peer- reviewed
[116]
Identification of pollen taxa by different microscopy techniques
Sep 1, 2021 · In this work, the suitability of three microscopic techniques for automatic analysis of pollen grains was studied.Missing: reviewed | Show results with:reviewed
[117]
Staining and fluorescent microscopy methods for pollen viability ...
Acetocarmine method is widely used to determine male fertility and pollen viability in cultivated, as well as wild sunflower species and interspecific hybrids.
[118]
Microscopy Research and Technique | Wiley Online Library
Jan 11, 2025 · Pollen morphology was evaluated by scanning electron microscopy and light microscopy by the weak lactic acetolysis method. Histochemical tests ...
[119]
Pollen Development and Stainability in Vicia faba L. and Lupinus ...
Oct 27, 2023 · Alexander's dye stains viable cells pink to dark purple. In nonviable cells, the cell interiors remain transparent, while cell walls stain green ...
[120]
An insight into pollen morphology and evaluation of pollen viability ...
There is evidence that the staining method overestimates pollen germination percentages, whereas the in-vitro tests underestimate them (Galletta, 1983).
[121]
A primer on pollen assignment by nanopore-based DNA sequencing
Mar 13, 2023 · Pollen metabarcoding is made up of five steps: pollen collection, DNA isolation, barcode amplification, sequencing and downstream bioinformatic ...<|control11|><|separator|>
[122]
Experimental quantification of pollen with DNA metabarcoding using ...
Mar 6, 2020 · Metabarcoding has been used in pollen studies to identify pollen in honey, insect loads, insect nests, airborne samples, and to quantify pollen ...
[123]
Review and future prospects for DNA barcoding methods in forensic ...
DNA barcoding of pollen could transform forensic palynology by making it accessible to a very wide range of forensic laboratories that have available molecular ...
[124]
Pollen DNA barcoding: current applications and future prospects
As with any genetic analysis, DNA barcoding requires destructive sampling of pollen grains, which means the pollen can no longer be analyzed with morphological ...
[125]
Anthropogenic climate change is worsening North American pollen ...
Feb 8, 2021 · We find widespread advances and lengthening of pollen seasons (+20 d) and increases in pollen concentrations (+21%) across North America, which ...
[126]
Pollen season trends as markers of climate change impact: Betula ...
Jul 20, 2022 · This study aimed to identify pollen trends in the UK over the last twenty-six years for a range of pollen sites, with a focus on the key pollen types of ...Pollen Season Trends As... · 3. Results And Discussion · 3.1. Betula Pollen Seasons<|separator|>
[127]
An Overview of Rising CO2 and Climatic Change on Aeroallergens ...
This review is intended to provide a synopsis of CO 2 and climate factors associated with likely changes in aeroallergen biology (indoor and outdoor)
[128]
How urban planners' preference for male trees has made your hay ...
May 16, 2020 · Pollen producing trees that are dioecious (with male and female flowers on separate plants) are seen to add to the effect of allergies of city ...
[129]
Too many male trees making spring allergy season hell in NYC
Apr 19, 2023 · In a trend dubbed “botanical sexism,” Big Apple city planners planted far more pollen-producing male trees because they're generally easier ...
[130]
Is “Botanical Sexism” Really to Blame for Increased Pollen Allergies ...
Sep 13, 2024 · A video explaining how botanical sexism was responsible for the rise in pollen allergies, however, it turned out to be little more than a far-fetched theory.
[131]
Botanical Sexism: Fact Or Fiction? | - Wisconsin DNR Forestry News
May 13, 2024 · It states that over time, humans have preferentially propagated and planted male trees, thus leading to increases in pollen production and subsequent allergens ...
[132]
Strong variations in urban allergenicity riskscapes due to poor ...
May 13, 2021 · We show that estimates of pollen exposure risk range from 1 to 74% for trees considered to be highly allergenic in the same city. This variation ...
[133]
[PDF] The effects of tree planting on allergenic pollen production in New ...
Jan 8, 2024 · Planting low-pollen trees could reduce aeroallergen exposure in cities, but the effects of historical tree planting.
[134]
Recommendations for allergy-friendly urban planting in the context ...
Jun 2, 2025 · The cause of the higher number of sensitizations to tree and grass pollen in large cities compared to rural or small-town areas is not known ...<|separator|>
[135]
Impact of Biodiversity Loss on Pollen Allergies: A Bibliometric Analysis
Oct 24, 2024 · These findings suggest that environmental biodiversity may help to protect against allergies by promoting beneficial microbial diversity and ...
[136]
Interaction Between Air Pollutants and Pollen Grains - NIH
Asthma and allergic diseases cases have risen in recent decades. Plant pollen is considered as the main aeroallergen causing allergic reactions.
[137]
The influence of air pollution on pollen allergy sufferers - PMC
Dec 1, 2021 · This is especially important for pollen allergy sufferers because air pollution plays a central role in the interactions between pollen and ...
[138]
Fossil fuels, allergies, and a host of other ills
The diesel particles (from burning fossil fuels) also contain nitrates that irritate mast cells, boosting the allergenic assault. Before leaving the ...
[139]
Report Environmental DNA reveals links between abundance and ...
May 10, 2021 · Grass (Poaceae) pollen is the most important outdoor aeroallergen, exacerbating a range of respiratory conditions, including allergic asthma ...
[140]
How heat, thunder, smog and new species are making hay fever ...
Apr 10, 2025 · First, particulate pollution from cars and industry is interacting with pollen, causing it to produce more allergens. One study of birch pollen ...