SEM image of pollen grains from a variety of common plants: sunflower (Helianthus annuus), morning glory (Ipomoea purpurea), prairie hollyhock (Sidalcea malviflora), oriental lily (Lilium auratum), evening primrose (Oenothera fruticosa), and castor bean (Ricinus communis). The scanning electron microscope ( SEM) is a type of Electron microscope that images the sample surface by scanning it with a high-energy beam of Electrons The sunflower ( Helianthus annuus) is an Annual plant in the family Asteraceae and native to the Americas, with a large flowering Ipomoea purpurea, the Purple, Tall, or Common Morning Glory, is a species in the genus Ipomoea, native to Mexico Lilium auratum is one of the true lilies, native to Japan. The flower colour is typically white with gold radial markings and orange spots The castor oil plant, Ricinus communis, is a Plant Species of the Euphorbiaceae (the evolution of this plant family is relatively unexplored

Closeup image of a cactus flower and its stamens

Honey bee on sedum with pollen basket

Pollen from Phacelia (in purple)

Pollen sticking to a bee. The pollen basket or corbicula is part of the tibia on the hind legs of the four related lineages of apid bees that used to comprise the family Apidae Phacelia, the phacelias or scorpionweeds, is a large Plant Genus. Insects involuntarily transporting pollen from flower to flower play an important role in many plants' reproductive cycles.

Marmelade fly sitting on a grey-haired rockrose, its face and legs covered in pollen.

Pollen is a fine to coarse powder consisting of microgametophytes (pollen grains), which produce the male gametes (sperm cells) of seed plants. In Plants and Algae that undergo Alternation of generations, a gametophyte is the multicellular structure or phase that is Haploid, containing A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete The spermatophytes (from the Greek word "Σπερματόφυτα" (also known as phanerogams) comprise those Plants that produce Seeds They are The pollen grain with its hard coat protects the sperm cells during the process of their movement between the stamens of the flower to the pistil of the next flower.

The structure of pollen

Each pollen grain contains vegetative (non-reproductive) cells (only a single cell in most flowering plants but several in other seed plants) and a generative (reproductive) cell containing two nuclei: a tube nucleus (that produces the pollen tube) and a generative nucleus (that divides to form the two sperm cells). The pollen tube of most Seed plants acts as a conduit to transport sperm cells from the Pollen grain, either from the stigma (in Flowering plants The group of cells is surrounded by a cellulose cell wall and a thick, tough outer wall made of sporopollenin. Cellulose is an Organic compound with the formula, a Polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4 Sporopollenin is a major component of the tough outer (exine walls of Spores and pollen grains.

Pollen is produced in the microsporangium (contained in the anther of an angiosperm flower, male cone of a coniferous plant, or male cone of other seed plants). The stamen ( Plural stamina or stamens, from Latin stamen meaning "thread of the warp " is the male The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group A flower, also known as a bloom or Blossom, is the reproductive structure found in Flowering plants (plants of the division Magnoliophyta, also A cone (in formal botanical usage Strobilus, plural strobili is an organ on Plants in the division Pinophyta ( Conifers Pollen grains come in a wide variety of shapes, sizes, and surface markings characteristic of the species (see Electron micrograph at top right). A micrograph, microphotograph or photomicrograph is a Photograph or similar image taken through a Microscope or similar device to show Most, but certainly not all, are spherical. Pollen grains of pines, firs, and spruces are winged. This article is about the tree For other uses of the term "pine" see Pine (disambiguation. Firs ( Abies) are a genus of between 45-55 species of Evergreen conifers in the family Pinaceae. Spruce refers to Trees of the genus Picea, a genus of about 35 species of Coniferous Evergreen trees in the Family Pinaceae The smallest pollen grain, that of the Forget-me-not (Myosotis spp. Myosotis is a Genus of Flowering plants in the family Boraginaceae that are commonly called Forget-me-nots. ), is around 6 µm (0. A micrometre ( American spelling: micrometer; symbol µm) is one millionth of a Metre, or equivalently one thousandth of a Millimetre 006  mm) in diameter. The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to The study of pollen is called palynology and is highly useful in paleoecology, paleontology, archeology, and forensics. Palynology is the science that studies contemporary and fossil Palynomorphs including Pollen, Spores, Dinoflagellate Cysts Acritarchs Palaeontology redirects here For the Scientific journal, see Palaeontology (journal. Archaeology, archeology, or archæology (from Greek grc ἀρχαιολογία archaiologia – grc ἀρχαῖος archaīos

In angiosperms, during flower development the anther is composed of a mass of cells that appear undifferentiated, except for a partially differentiated dermis. As the flower develops, four groups of sporogenous cells form with in the anther, the fertile sporogenous cells are surrounded by layers of sterile cells that grow into the wall of the pollen sac, some of the cells grow into nutritive cells that supply nutrition for the microspores that form by meiotic division from the sporogenous cells. Four haploid microspores are produced from each diploid sporogenous cell called microsporocytes, after meiotic division. After the formation of the four microspores, which are contained by callose walls, the development of the pollen grain walls begins. The callose wall is broken down by an enzyme called callase and the freed pollen grains grow in size and develop their characteristic shape and form a resistant outer wall called the exine and an inner wall called the intine. The exine is made up of a resistant compound called sporopollenin; the intine is made up of cellulose and pectin. The exine is what is preserved in the fossil record.

Pollen grains may have furrows, the orientation of which (relative to the original tetrad of microspores) classify the pollen as colpate or sulcate. The number of furrows or pores helps classify the flowering plants, with eudicots having three colpi (tricolpate), and other groups having one sulcus. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group Eudicots and Eudicotyledons are terms introduced by Doyle & Hotton (1991 to refer to a group of Flowering plants that had been called "tricolpates" or "non-Magnoliid ^{[1] [2]}

Except in the case of some submerged aquatic plants, the mature pollen-grain has a double wall, a thin delicate wall of unaltered cellulose (the endospore or intine) and a tough outer cuticularized exospore or exine. The exine often bears spines or warts, or is variously sculptured, and the character of the markings is often of value for identifying genus, species, or even cultivar or individual. In some flowering plants, germination of the pollen grain often begins before it leaves the microsporangium, with the generative cell forming the two sperm cells. Germination is the process whereby growth emerges from a period of dormancy

Pollination

Main article: Pollination

The transfer of pollen grains to the female reproductive structure (pistil in angiosperms) is called pollination. Pollination in angiosperms and Gymnosperms is the process that transfers pollen grains, which contain the male Gametes (sperm to where the female A gynoecium (from Ancient Greek gyne, "woman" is the Female reproductive part of a Flower. Pollination in angiosperms and Gymnosperms is the process that transfers pollen grains, which contain the male Gametes (sperm to where the female This transfer can be mediated by the wind, in which case the plant is described as anemophilous (literally wind-loving). See also Pollination syndrome Anemophily or wind pollination is a form of Pollination whereby Pollen is distributed by Wind Anemophilous plants typically produce great quantities of very lightweight pollen grains, sometimes with air-sacs. Non-flowering seed plants (e. g. pine trees) are characteristically anemophilous. This article is about the tree For other uses of the term "pine" see Pine (disambiguation. Anemophilous flowering plants generally have inconspicuous flowers. Entomophilous (literally insect-loving) plants produce pollen that is relatively heavy, sticky and protein-rich, for dispersal by insect pollinators attracted to their flowers. See also Pollination syndrome Entomophily is a form of pollination whereby Pollen is distributed by Insects particularly Bees Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described A pollinator is the biotic agent ( vector) that moves Pollen from the male Anthers of a Flower to the female stigma of a flower to accomplish A flower, also known as a bloom or Blossom, is the reproductive structure found in Flowering plants (plants of the division Magnoliophyta, also Many insects and some mites are specialized to feed on pollen, and are called palynivores. Mites, along with Ticks belong to the subclass Acarina (also known as Acari and the class Arachnida Mites are among the most diverse and successful In Zoology, a palynivore is an Herbivorous animal which selectively eats the nutrient-rich Pollen produced by flowering plants including Gymnosperms

In non-flowering seed plants, pollen germinates in the pollen chamber, located beneath and inside the micropyle. Ovule literally means "small egg." In Seed plants the ovule is the structure that gives rise to and contains the female reproductive cells A pollen tube is produced, which grows into the nucellus to provide nutrients for the developing sperm cells. The pollen tube of most Seed plants acts as a conduit to transport sperm cells from the Pollen grain, either from the stigma (in Flowering plants Ovule literally means "small egg." In Seed plants the ovule is the structure that gives rise to and contains the female reproductive cells Sperm cells of Pinophyta and Gnetophyta are without flagella, and are carried by the pollen tube, while those of Cycadophyta and Ginkgophyta have many flagella. The Plant division Gnetophyta or gnetophytes comprise three related families of Woody plants grouped in the Gymnosperms The gnetophytes differ from A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it Cycads are a group of Seed plants characterized by a large crown of compound leaves and a stout trunk. The Ginkgoaceae is a family of Gymnosperms which appeared during the Mesozoic Era of which the only extant representative is Ginkgo biloba

When placed on the stigma of a flowering plant, under favorable circumstances, a pollen grain puts forth a pollen tube which grows down the tissue of the style to the ovary, and makes its way along the placenta, guided by projections or hairs, to the micropyle of an ovule. A gynoecium (from Ancient Greek gyne, "woman" is the Female reproductive part of a Flower. The pollen tube of most Seed plants acts as a conduit to transport sperm cells from the Pollen grain, either from the stigma (in Flowering plants In the Flowering plants an ovary is a part of the female reproductive organ of the flower or Gynoecium. The placenta is an Ephemeral organ present in placental Vertebrates, such as Eutherial Mammals and Sharks during Gestation Ovule literally means "small egg." In Seed plants the ovule is the structure that gives rise to and contains the female reproductive cells The nucleus of the tube cell has meanwhile passed into the tube, as does also the generative nucleus which divides (if it hasn't already) to form two sperm cells. The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells. The sperm cells are carried to their destination in the tip of the pollen-tube.

Pollen as a carrier of ecological information in plants

A Russian theoretical biologist, Vigen Geodakyan (Geodakian), has suggested that the quantity of pollen reaching a pistillate flower can transmit ecological information and also regulate evolutionary plasticity in cross-pollinating plants. A gynoecium (from Ancient Greek gyne, "woman" is the Female reproductive part of a Flower. Ecology (from Greek grc οἶκος oikos, "house(hold" and grc -λογία -logia) is the scientific study of The ability of an organism with a given Genotype to change its Phenotype in response to changes in the environment is called phenotypic plasticity. Plentiful pollen indicates optimum environmental conditions (for example a plant that is situated at the center of its natural range, in ideal growing conditions, with a large number of male plants nearby, and favorable weather conditions), whereas a small amount of pollen indicates extreme conditions (at the borders of its range, with a deficiency of male plants, and adverse weather conditions). Geodakian believes that the quantity of pollen reaching a pistillate flower defines the sex ratio, dispersion and sexual dimorphism of a plant population. Sex ratio is the Ratio of Males to Females in a Population. The primary sex ratio is the ratio at the time of conception secondary sex ratio is Sexual dimorphism is the systematic difference in form between individuals of different Sex in the same Species. High pollen quantity leads to a reduction of these characteristics and stabilization of a population. In Biology a population is the collection of inter-breeding organisms of a particular Species; in Sociology Small quantity leads to their increase and destabilization of a population. ^[3]

Dependence of the secondary sex ratio on the amount of fertilizing pollen was confirmed on four dioecious plant species from three families — Rumex acetosa (Polygonaceae),^[4][5] Melandrium album (Cariophyllaceae),^[6][7] Cannabis sativa^[8] and Humulus japonicus (Cannabinaceae). Sex ratio is the Ratio of Males to Females in a Population. The primary sex ratio is the ratio at the time of conception secondary sex ratio is ^[9] (see summary of all these data in review article^[10]).

Dependence of offspring phenotype variety on amount of pollen was observed by Ter-Avanesyan in 1949. All three studied species of plants (cotton plant, black-eyed pea, and wheat) showed dependence in the direction forecasted by the theory — fertilization with a small amount of pollen resulted in an increase in the diversity of the offspring. Ter-Avanesian writes that as a result of a limited pollination “instead of homogenous sorts we get populations”. ^[11][12]

Pollen in the fossil record

Pollen's sporopolenin outer sheath affords it some resistance to the rigours of the fossilisation process that destroy weaker objects; it is also produced in huge quantities. As such, there is an extensive fossil record of pollen grains, often disassociated from their parent plant. The discipline of palynology is devoted to the study of pollen, which can be used both for biostratigraphy and to gain information about the abundance and variety of plants alive - which can itself yield important information about paleoclimates. Palynology is the science that studies contemporary and fossil Palynomorphs including Pollen, Spores, Dinoflagellate Cysts Acritarchs Pollen is first found in the fossil record in the late Devonian period and increases in abundance until the present day. The Devonian is a geologic period and system of the Paleozoic era spanning from to  million years ago.

Hay fever

Main article: Hay fever

Allergy to pollen is called hay fever. Hay Fever is a comic play written by Noel Coward in 1924 and first produced in 1925 with Marie Tempest as the first Judith Bliss Allergy is a disorder of the Immune system often also referred to as Atopy. Hay Fever is a comic play written by Noel Coward in 1924 and first produced in 1925 with Marie Tempest as the first Judith Bliss Generally pollens that cause allergies are those of anemophilous plants (pollen is dispersed by air currents. ) Such plants produce large quantities of lightweight pollen (because wind dispersal is random and the likelihood of one pollen grain landing on another flower is small) which can be carried for great distances and are easily inhaled, bringing it into contact with the sensitive nasal passages.

In the US, people often mistakenly blame the conspicuous goldenrod flower for allergies. The goldenrod is a yellow Flowering plant in the Family Asteraceae. Since this plant is entomophilous (its pollen is dispersed by animals), its heavy, sticky pollen does not become independently airborne. Most late summer and fall pollen allergies are probably caused by ragweed, a widespread anemophilous plant. Ragweeds ( Ambrosia) also called bitterweeds and bloodweeds, are a Genus of flowering Plants from the sunflower

Arizona was once regarded as a haven for people with pollen allergies, although several ragweed species grow in the desert. The State of Arizona ( is a state located in the southwestern region of the United States. A desert is a Landscape or region that receives very little precipitation. However, as suburbs grew and people began establishing irrigated lawns and gardens, more irritating species of ragweed gained a foothold and Arizona lost its claim of freedom from hay fever. South San Jose (cropjpg||thumb|A suburban development in San Jose California. Irrigation is an artificial application of water to the soil usually for assisting in growing crops

Anemophilous spring blooming plants such as oak, birch, hickory, pecan, and early summer grasses may also induce pollen allergies. The term oak can be used as part of the common name of any of about 400 species of Trees and Shrubs in the Genus Quercus (from Latin Birch is the name of any Tree of the genus Betula ( Bé-tu-la) in the family Betulaceae, closely related to the Trees in the genus Carya (from Ancient Greek κάρυον " Nut " are commonly known as Hickory. The Pecan ( Carya illinoinensis, commonly misspelled illinoensis) is a species of Hickory, native to south-central North America Grass is the common word that generally describes Monocotyledonous green Plants The family Gramineae ( Poaceae) are the "true grasses" and include Most cultivated plants with showy flowers are entomophilous and do not cause pollen allergies.

Pollen in human diets

A variety of producers have started selling pollen for human consumption, often marketed as a healthy food. Food is any substance usually composed primarily of Carbohydrates Fats water and/or Proteins that can be eaten or drunk by an Like many other foods, pollen contains water, amino acids, proteins, lipids, carbohydrates, minerals, vitamins, enzymes and other micronutrients. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Lipids are broadly defined as any fat- Soluble ( lipophilic) naturally-occurring Molecule, such as fats oils waxes cholesterol sterols fat-soluble Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most Dietary minerals are the Chemical elements required by living Organisms other than the four elements Carbon, Hydrogen, Nitrogen, and A vitamin is an Organic compound required as a Nutrient in tiny amounts by an Organism. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Micronutrients are Nutrients needed for life in small quantities Composition depends on plant species collected by bees. Supplements of pollen have been used in a number of treatments, e. g. treatment of anemia, disorders of digestive system, mental disorders like depression, asthenia and alcohol dependence. Anemia ( AmE) or anæmia/anaemia ( BrE) (from the Ancient Greek grc-Latn anaîmia, meaning “without blood” is defined as a qualitative In the fields of Psychology and Psychiatry, the terms depression or depressed refer to both expected and pathologically chronic or severe Asthenia ( Greek: ασθένεια, lit lack of strength but also disease) is a medical term denoting symptoms of physical weakness Alcohol dependence, as described in the DSM-IV, is a psychiatric diagnosis describing a Physical dependence on alcohol.

The FDA has not found any harmful effects of pollen consumption, except from the usual allergies. However, FDA does not allow pollen marketers in the United States to make health claims about their produce, as no scientific basis for these has ever been proved. Furthermore, there are possible dangers not only from allergic reactions but also from contaminants such as pesticides and from fungi and bacteria growth related to poor storage procedures. A manufacturers's claim that pollen collecting helps the bee colonies is also controversial. ^[13]

References

1. ^ Kenneth R. Sporne (1972). "Some Observations on the Evolution of Pollen Types in Dicotyledons". New Phytologist 71 (1): 181–185. doi:10.1111/j.1469-8137.1972.tb04826.x. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
2. ^ Walter S. Judd and Richard G. Olmstead (2004). "A survey of tricolpate (eudicot) phylogenetic relationships". American Journal of Botany 91: 1627-1644.   (full text)
3. ^ Geodakyan V. A. (1977). The Amount of Pollen as a Regulator of Evolutionary Plasticity of Cross-Pollinating Plants. “Doklady Biological Sciences” 234 N 1-6, 193–196.
4. ^ Соrrеns С. (1922) Geschlechtsbestimmung und Zahlenverhaltnis der Geschlechter beim Sauerampfer (Rumex acetosa). “Biol. Zbl. ” 42, 465-480.
5. ^ Rychlewski J. , Kazlmierez Z. (1975) Sex ratio in seeds of Rumex acetosa L. as a result of sparse or abundant pollination. “Acta Biol. Cracov” Scr. Bot. , 18, 101-114.
6. ^ Correns C. (1928) Bestimmung, Vererbung und Verteilung des Geschlechter bei den hoheren Pflanzen. Handb. Vererbungswiss. , 2, 1-138.
7. ^ Mulcahy D. L. (1967) Optimal sex ratio in Silene alba. “Heredity” 22 № 3, 41.
8. ^ Riede W. (1925) Beitrage zum Geschlechts- und Anpassungs-problem. “Flora” 18/19
9. ^ Kihara H. , Hirayoshi J. (1932) Die Geschlechtschromosomen von Humulus japonicus. Sieb. et. Zuce. In: 8th Congr. Jap. Ass. Adv. Sci. , p. 363—367 (cit. : Plant Breeding Abstr. , 1934, 5, № 3, p. 248, ref. № 768).
10. ^ Geodakyan, V. A. & Geodakyan, S. V. , (1985) Is there a negative feedback in sex determination? “Zurnal obschej biol. ” 46 201-216 (in Russian). ).
11. ^ Ter-Avanesyan D. V. (1949). Tr. Prikl. Bot, Genet, Selekt. , 28 119.
12. ^ Ter-Avanesian D. V. (1978) Significance of pollen amount for fertilization. “Bull. Torrey Bot. Club. ” 105 N 1, 2–8.
13. ^ Malcolm T. Sanford. Producing Pollen. University of Florida, Institute of Food and Agricultural Sciences. Retrieved on 2007-08-30. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1363 - Beginning date of the Battle of Lake Poyang; the forces of two Chinese rebel leaders— Chen Youliang and . Document ENY118. Original publication date November 1, 1994. Revised February 1, 1995. Reviewed May 1, 2003.

See also

• Pollen count
• Pollen source
• Polyphenol antioxidant
• Evolution of sex
• Sex ratio
• Palynivore

External links

Clumps of yellow pollen on a flower head. Pollen count is the measurement of the number of grains of Pollen in a Cubic meter of Air. The term pollen source is often used in the context of Beekeeping and refers to flowering plants as a source of Pollen for bees or other insects A polyphenol antioxidant is a type of Antioxidant containing a Polyphenolic substructure Sex ratio is the Ratio of Males to Females in a Population. The primary sex ratio is the ratio at the time of conception secondary sex ratio is In Zoology, a palynivore is an Herbivorous animal which selectively eats the nutrient-rich Pollen produced by flowering plants including Gymnosperms

• Daily Pollen Count
• Pollen and Spore Identification Literature
• Paleobotany and Palynology at the Florida Museum of Natural History
• Palynology at the University of Arizona
• Palynology at French Institute of Pondicherry
• Palynology at the University of Sheffield
• SEM coloured and confocal microscope images of pollen

This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain. The Encyclopædia Britannica Eleventh Edition (1910–1911 is a 29-volume reference work that marked the beginning of the Encyclopædia Britannica The public domain is a range of abstract materials &ndash commonly referred to as Intellectual property &ndash which are not owned or controlled by anyone

• Palynology in Utrecht, the Netherlands
• The flight of the pollen cloud Outcrossing from transgenic maize and quantifying outcrossing rates
• The Evolutionary Theory of Sex: Mechanisms of Regulation of the Population Parameters
• PalDat (database comprising palynological data from a variety of plant families)