Pollen is a fine to coarse powdery substance comprising pollen grains
which are male microgametophytes of seed plants, which produce male
gametes (sperm cells).
Pollen grains have a hard coat made of
sporopollenin that protects the gametophytes during the process of
their movement from the stamens to the pistil of flowering plants, or
from the male cone to the female cone of coniferous plants. If pollen
lands on a compatible pistil or female cone, it germinates, producing
a pollen tube that transfers the sperm to the ovule containing the
female gametophyte. Individual pollen grains are small enough to
require magnification to see detail. The study of pollen is called
palynology and is highly useful in paleoecology, paleontology,
archaeology, and forensics.
Pollen in plants is used for transferring haploid male genetic
material from the anther of a single flower to the stigma of another
in cross-pollination. In a case of self-pollination, this process
takes place from the anther of a flower to the stigma of the same
1 The structure and formation of pollen
Pollen in the fossil record
4 Allergy to pollen
5.1 In humans
6 Forensic palynology
7 See also
10 External links
The structure and formation of pollen
Triporate pollen of Oenothera speciosa
Lilium auratum showing single sulcus (monosulcate)
Arabis pollen has three colpi and prominent surface structure.
Lycopersicon esculentum at coenocytic tetrad
stage of development observed through oil immersion microscope; the
chromosomes of what will become four pollen grains can be seen.
Apple pollen under microscopy
Pollen itself is not the male gamete. 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. In flowering plants the vegetative tube cell
produces the pollen tube, and the generative cell divides to form the
two sperm cells.
Pollen is produced in the microsporangia in the male cone of a conifer
or other gymnosperm or in the anthers of an angiosperm flower. Pollen
grains come in a wide variety of shapes, sizes, and surface markings
characteristic of the species (see electron micrograph, right). Pollen
grains of pines, firs, and spruces are winged. The smallest pollen
grain, that of the forget-me-not (Myosotis spp.),[which?] is around
6 µm (0.006 mm) in diameter. Wind-borne
pollen grains can be as large as about 90–100 µm.
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 within 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.
In a process called microsporogenesis, four haploid microspores are
produced from each diploid sporogenous cell (microsporocyte, pollen
mother cell or meiocyte), 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 what is preserved in the fossil record. Two basic
types of microsporogenesis are recognised, simultaneous and
successive. In simultaneous microsporogenesis meiotic steps I and II
are completed prior to cytokinesis, whereas in successive
microsporogenesis cytokinesis follows. While there may be a continuum
with intermediate forms, the type of microsporogenesis has systematic
significance. The predominant form amongst the monocots is successive,
but there are important exceptions.
During microgametogenesis, the unicellular microspores undergo mitosis
and develop into mature microgametophytes containing the gametes.
In some flowering plants,[which?] germination of the pollen grain may
begin even before it leaves the microsporangium, with the generative
cell forming the two sperm cells.
Except in the case of some submerged aquatic plants, the mature pollen
grain has a double wall. The vegetative and generative cells are
surrounded by a thin delicate wall of unaltered cellulose called the
endospore or intine, and a tough resistant outer cuticularized wall
composed largely of sporopollenin called the 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. The spines may be less than a
micron in length (spinulus, plural spinuli) referred to as spinulose
(scabrate), or longer than a micron (echina, echinae) referred to as
echinate. Various terms also describe the sculpturing such as
reticulate, a net like appearance consisting of elements (murus, muri)
separated from each other by a lumen (plural lumina).
The pollen wall protects the sperm while the pollen grain is moving
from the anther to the stigma; it protects the vital genetic material
from drying out and solar radiation. The pollen grain surface is
covered with waxes and proteins, which are held in place by structures
called sculpture elements on the surface of the grain. The outer
pollen wall, which prevents the pollen grain from shrinking and
crushing the genetic material during desiccation, is composed of two
layers. These two layers are the tectum and the foot layer, which is
just above the intine. The tectum and foot layer are separated by a
region called the columella, which is composed of strengthening rods.
The outer wall is constructed with a resistant biopolymer called
Pollen apertures are regions of the pollen wall that may involve exine
thinning or a significant reduction in exine thickness. They allow
shrinking and swelling of the grain caused by changes in moisture
content. Elongated apertures or furrows in the pollen grain are called
colpi (singular: colpus) or sulci (singular: sulcus). Apertures that
are more circular are called pores. Colpi, sulci and pores are major
features in the identification of classes of pollen.
Pollen may be
referred to as inaperturate (apertures absent) or aperturate
(apertures present). The aperture may have a lid (operculum), hence is
described as operculate. However the term inaperturate covers a
wide range of morphological types, such as functionally inaperturate
(cryptoaperturate) and omniaperturate. Inaperaturate pollen grains
often have thin walls, which facilitates pollen tube germination at
any position. Terms such as uniaperturate and triaperturate refer
to the number of apertures present (one and three respectively).
The orientation of furrows (relative to the original tetrad of
microspores) classifies the pollen as sulcate or colpate. Sulcate
pollen has a furrow across the middle of what was the outer face when
the pollen grain was in its tetrad. If the pollen has only a single
sulcus, it is described as monosulcate, has two sulci, as bisulcate,
or more, as polysulcate. Colpate pollen has furrows other than
across the middle of the outer faces.
Eudicots have pollen with
three colpi (tricolpate) or with shapes that are evolutionarily
derived from tricolpate pollen. The evolutionary trend in plants
has been from monosulcate to polycolpate or polyporate pollen.
Main article: Pollination
European honey bee carrying pollen in a pollen basket back to the hive
Marmalade hoverfly, pollen on its face and legs, sitting on a
Diadasia bee straddles flower carpels while visiting yellow Opuntia
The transfer of pollen grains to the female reproductive structure
(pistil in angiosperms) is called pollination. This transfer can be
mediated by the wind, in which case the plant is described as
anemophilous (literally wind-loving). 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. 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. Many insects and some mites are specialized to feed on
pollen, and are called palynivores.
In non-flowering seed plants, pollen germinates in the pollen chamber,
located beneath the micropyle, underneath the integuments of the
ovule. A pollen tube is produced, which grows into the nucellus to
provide nutrients for the developing sperm cells.
Sperm cells of
Gnetophyta are without flagella, and are carried by the
pollen tube, while those of Cycadophyta and
Ginkgophyta have many
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. 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 sperm cells are carried to their
destination in the tip of the pollen tube. Double-strand breaks in DNA
that arise during pollen tube growth appear to be efficiently repaired
in the generative cell that carries the male genomic information to be
passed on to the next plant generation. However, the vegetative
cell that is responsible for tube elongation appears to lack this DNA
Pollen in the fossil record
Main article: Palynology
Pollen's sporopollenin outer sheath affords it some resistance to the
rigours of the fossilisation process that destroy weaker objects; it
is also produced in huge quantities. 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.
Pollen is first found in
the fossil record in the late
Devonian period[verification needed] and
increases in abundance until the present day.
Allergy to pollen
See also: Allergy season
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Nasal allergy to pollen is called pollinosis, and allergy specifically
to grass pollen is called hay fever. 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. 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.
Arizona was once regarded as a haven for people with pollen allergies,
although several ragweed species grow in the desert. 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.
Anemophilous spring blooming plants such as oak, birch, hickory,
pecan, and early summer grasses may also induce pollen allergies. Most
cultivated plants with showy flowers are entomophilous and do not
cause pollen allergies.
The number of people in the United States affected by hay fever is
between 20 and 40 million, and such allergy has proven to be the
most frequent allergic response in the nation. There are certain
evidential suggestions pointing out hay fever and similar allergies to
be of hereditary origin. Individuals who suffer from eczema or are
asthmatic tend to be more susceptible to developing long-term hay
In Denmark, decades of rising temperatures cause pollen to appear
earlier and in greater numbers, as well as introduction of new species
such as ragweed.
The most efficient way to handle a pollen allergy is by preventing
contact with the material. Individuals carrying the ailment may at
first believe that they have a simple summer cold, but hay fever
becomes more evident when the apparent cold does not disappear. The
confirmation of hay fever can be obtained after examination by a
Allergic rhinitis § treatment
Antihistamines are effective at treating mild cases of pollinosis,
this type of non-prescribed drugs includes loratadine, cetirizine and
chlorpheniramine. They do not prevent the discharge of histamine, but
it has been proven that they do prevent a part of the chain reaction
activated by this biogenic amine, which considerably lowers hay fever
Decongestants can be administered in different ways such as tablets
and nasal sprays.
Allergy immunotherapy (AIT) treatment involves administering doses of
allergens to accustom the body to pollen, thereby inducing specific
long-term tolerance. Allergy immunotherapy can be administered
orally (as sublingual tablets or sublingual drops), or by injections
under the skin (subcutaneous). Discovered by Leonard Noon and John
Freeman in 1911, allergy immunotherapy represents the only causative
treatment for respiratory allergies.
Most major classes of predatory and parasitic arthropods contain
species that eat pollen, despite the common perception that bees are
the primary pollen-consuming arthropod group. Many other Hymenoptera
other than bees consume pollen as adults, though only a small number
feed on pollen as larvae (including some ant larvae). Spiders are
normally considered carnivores but pollen is an important source of
food for several species, particularly for spiderlings, which catch
pollen on their webs. It is not clear how spiderlings manage to eat
pollen however, since their mouths are not large enough to consume
pollen grains. Some predatory mites also feed on
pollen, with some species being able to subsist solely on pollen, such
as Euseius tularensis, which feeds on the pollen of dozens of plant
species. Members of some beetle families such as
Melyridae feed almost exclusively on pollen as adults, while various
lineages within larger families such as Curculionidae, Chrysomelidae,
Scarabaeidae are pollen specialists even though most
members of their families are not (e.g., only 36 of 40000 species of
ground beetles, which are typically predatory, have been shown to eat
pollen—but this is thought to be a severe underestimate as the
feeding habits are only known for 1000 species). Similarly, Ladybird
beetles mainly eat insects, but many species also eat pollen, as
either part or all of their diet.
Hemiptera are mostly herbivores or
omnivores but pollen feeding is known (and has only been well studied
in the Anthocoridae). Many adult flies, especially Syrphidae, feed on
pollen, and three UK syrphid species feed strictly on pollen
(syrphids, like all flies, cannot eat pollen directly due to the
structure of their mouthparts, but can consume pollen contents that
are dissolved in a fluid). Some species of fungus, including Fomes
fomentarius, are able to break down grains of pollen as a secondary
nutrition source that is particularly high in nitrogen.
be valuable diet supplement for detritivores, providing them with
nutrients needed for growth, development and maturation. It was
suggested that obtaining nutrients from pollen, deposited on the
forest floor during periods of pollen rains, allows fungi to decompose
nutritionally scarce litter.
Some species of
Heliconius butterflies consume pollen as adults, which
appears to be a valuable nutrient source, and these species are more
distasteful to predators than the non-pollen consuming
Although bats, butterflies and hummingbirds are not pollen eaters per
se, their consumption of nectar in flowers is an important aspect of
the pollination process.
A variety of producers have started selling bee pollen for human
consumption, often marketed as a food (rather than a dietary
supplement). The largest constituent is carbohydrates, with protein
content ranging from 7 to 35 percent depending on the plant species
collected by bees.
Honey produced by bees from natural sources contains pollen derived
p-coumaric acid, an antioxidant.
Food and Drug Administration (FDA) has not found any harmful
effects of bee pollen consumption, except from the usual allergies.
However, FDA does not allow bee pollen marketers in the United States
to make health claims about their produce, as no scientific basis for
these has ever been proven. 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.
Pine pollen (송화가루; Songhwa Garu) is traditionally consumed in
Korea as an ingredient in sweets and beverages.
The growing industries in pollen harvesting for human and bee
consumption rely on harvesting pollen baskets from honey bees as they
return to their hives using a pollen trap. When this pollen has
been tested for parasites, it has been found that a multitude of
pollinator viruses and eukaryotic parasites are present in the
pollen. It is currently unclear if the parasites are
introduced by the bee that collected the pollen or if it is from
contamination to the flower. Though this is not likely to pose
a risk to humans, it is a major issue for the bumblebee rearing
industry that relies on thousands of tonnes of honey bee collected
pollen per year. Several sterilization methods have been employed,
though no method has been 100% effective at sterilizing, without
reducing the nutritional value, of the pollen 
Main article: Forensic palynology
An SEM micrograph of Redbud pollen. Scanning electron microscopes are
major instruments in palynology.
In forensic biology, pollen can tell a lot about where a person or
object has been, because regions of the world, or even more particular
locations such a certain set of bushes, will have a distinctive
collection of pollen species.
Pollen evidence can also reveal the
season in which a particular object picked up the pollen. Pollen
has been used to trace activity at mass graves in Bosnia, catch a
burglar who brushed against a
Hypericum bush during a crime, and
has even been proposed as an additive for bullets to enable tracking
Evolution of sex
Pollen DNA barcoding
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Wikimedia Commons has media related to Pollen.
Spore Identification Literature
Pollen micrographs at SEM and confocal microscope
The flight of a pollen cloud
PalDat (database comprising palynological data from a variety of plant
Pollen-Wiki - A digital Pollen-Atlas, abgerufen am 09. Februar 2018.
YouTube video of pollen clouds from Juncus gerardii plants
This article incorporates text from a publication now in
the public domain: Chisholm, Hugh, ed. (1911). "article name
needed". Encyclopædia Britannica (11th ed.). Cambridge University
History of botany
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