Pollen
Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction.[1] It consists of pollen grains (highly reduced microgametophytes), 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 gymnosperms. 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.[2] In a case of self-pollination, this process takes place from the anther of a flower to the stigma of the same flower.[2]
Pollen is infrequently used as food and food supplement. Because of agricultural practices, it is often contaminated by agricultural pesticides.[3]
Structure and formation
Pollen itself is not the male gamete.[4] It is a gametophyte, something that could be considered an entire organism, which then produces 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 nuclei.
Pollen comes in many different shapes. Some pollen grains are based on
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Triporate pollen of Oenothera speciosa
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Pollen of Lilium auratum showing single sulcus (monosulcate)
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Arabis pollen has three colpi and prominent surface structure.
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Apple pollen
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Pollen of Lilium bulbiferum on an insect's hair
Formation
Pollen is produced in the
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
During microgametogenesis, the unicellular microspores undergo mitosis and develop into mature
Structure
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). These reticulations may also be referred to as brochi.
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,[citation needed] 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 sporopollenin.
Pollen apertures are regions of the pollen wall that may involve exine thinning or a significant reduction in exine thickness.[10] They allow shrinking and swelling of the grain caused by changes in moisture content. The process of shrinking the grain is called harmomegathy.[11] 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.[12] 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.[13] However the term inaperturate covers a wide range of morphological types, such as functionally inaperturate (cryptoaperturate) and omniaperturate.[8] Inaperaturate pollen grains often have thin walls, which facilitates pollen tube germination at any position.[10] Terms such as uniaperturate and triaperturate refer to the number of apertures present (one and three respectively). Spiraperturate refers to one or more apertures being spirally shaped.
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.
Additionally,
Pollination
The transfer of pollen grains to the female reproductive structure (
In non-flowering seed plants, pollen germinates in the pollen chamber, located beneath the
When placed on the
In the fossil record
The sporopollenin outer sheath of pollen grains affords them 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. Also, pollen analysis has been widely used for reconstructing past changes in vegetation and their associated drivers.[22] Pollen is first found in the fossil record in the late Devonian period,[23][24] but at that time it is indistinguishable from spores.[23] It increases in abundance until the present day.
Allergy to pollen
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Pollen allergies are common in polar and temperate climate zones, where production of pollen is seasonal. In the tropics pollen production varies less by the season, and allergic reactions less. In northern Europe, common pollens for allergies are those of birch and alder, and in late summer wormwood and different forms of hay. Grass pollen is also associated with asthma exacerbations in some people, a phenomenon termed thunderstorm asthma.[25]
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.[26]
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
Symptoms of pollen allergy include sneezing, itchy, or runny nose, nasal congestion, red, itchy, and watery eyes. Substances, including pollen, that cause allergies can trigger asthma. A study found a 54% increased chance of asthma attacks when exposed to pollen.[27]
The number of people in the United States affected by hay fever is between 20 and 40 million, including around 6.1 million children
Since 1990, pollen seasons have gotten longer and more pollen-filled, and climate change is responsible, according to a new study.[32] The researchers attributed roughly half of the lengthening pollen seasons and 8% of the trend in pollen concentrations to climate changes driven by human activity.[33]
In Denmark, decades of rising temperatures cause pollen to appear earlier and in greater amounts, exacerbated by the introduction of new species such as ragweed.[34]
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 general physician.[35]
Treatment
Allergy immunotherapy (AIT) treatment involves administering doses of allergens to accustom the body to pollen, thereby inducing specific long-term tolerance.[36] 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.
Nutrition
Most major classes of
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 species.[40][41]
Although
In humans
Bee pollen for human consumption is marketed as a food ingredient and as 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.[42]
The
Pine pollen (송화가루; Songhwa Garu) is traditionally consumed in Korea as an ingredient in sweets and beverages.[46]
Parasites
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.[47] When this pollen has been tested for parasites, it has been found that a multitude of viruses and eukaryotic parasites are present in the pollen.[48][49] It is currently unclear if the parasites are introduced by the bee that collected the pollen or if it is from the flower.[49][50] 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.[51] Several sterilization methods have been employed, though no method has been 100% effective at sterilisation without reducing the nutritional value of the pollen [52]
Forensic palynology
In
Spiritual purposes
In some
Pollen grain staining
For agricultural research purposes, assessing the viability of pollen grains can be necessary and illuminating. A very common, efficient method to do so is known as Alexander's stain. This differential stain consists of
.) In angiosperms and gymnosperms non-aborted pollen grain will appear red or pink, and aborted pollen grains will appear blue or slightly green.See also
- European Pollen Database
- Evolution of sex
- Honeybee starvation
- Pollen calendar
- Pollen count
- Pollen DNA barcoding
- Pollen source
- Polyphenol antioxidant
- Bee pollen
References
- ^ "Best and Worst Flowers for People With Allergies". WebMD.com. Retrieved 2023-10-30.
- ^ a b Chisholm, Hugh, ed. (1911). . Encyclopædia Britannica. Vol. 22 (11th ed.). Cambridge University Press. pp. 2–5.
- ^ S2CID 19956612.
- ISBN 978-0-19-914766-3.
- pollen grain.
- ^ a b "Spores and Pollens".
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- ^ .
- ^ "Pollen Development — University of Leicester". Archived from the original on 2014-10-06. Retrieved 2013-12-12.
- ^ PMID 15003239.
- PMID 20404200.
- ^ Davis, Owen. "Aperture". geo.arizona.edu. Archived from the original on 2009-02-03. Retrieved 2009-02-16.
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- ^ .
- ISBN 978-0-08-051404-8. Retrieved 6 January 2014.
- ISBN 9781578083510. Retrieved 23 January 2014.
- ^ Kaltenrieder & von Ballmoos 2003.
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- ^ ISBN 978-1-4020-6684-9.
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- ^ Oder, Tom. "Dear allergy sufferers: Don't blame goldenrod". mnn.com. Mother Nature Network. Retrieved 18 July 2016.
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- ^ "Allergy Facts | AAFA.org". www.aafa.org. Retrieved 2021-07-12.
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- ^ Allergies and Hay Fever WebMD. Retrieved on 2010-03-09
- PMID 33558232.
- ^ Boston, 677 Huntington Avenue; Ma 02115 +1495‑1000 (2021-02-18). "Pollen seasons are getting longer, driven by climate change". News. Retrieved 2021-07-12.
{{cite web}}
: CS1 maint: numeric names: authors list (link) - ^ Siewertsen, Bjarne. "Hård nyser for allergikere i varm fremtid Archived 2015-04-19 at the Wayback Machine" (English: Hard sneeze for allergic people in warm future) Danish Meteorological Institute, 18 April 2015. Retrieved: 19 April 2015.
- ^ Bee, grass pollen allergy symptoms Archived 2009-10-10 at the Wayback Machine. allergiesandtreatments.com. Retrieved on 2010-03-09
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- ^ Salcedo, C. (1 June 2010). "Evidence of pollen digestion at nocturnal aggregations of Heliconius sara in Costa Rica (Lepidoptera: Nymphalidae)". Tropical Lepidoptera Research: 35–37.
- S2CID 206046558.
- ^ Sanford, Malcolm T. "Producing Pollen". Archived from the original on January 13, 2007. Retrieved 2015-07-15., University of Florida, Institute of Food and Agricultural Sciences; citing P. Witherell, "Other Products of the Hive," Chapter XVIII, The Hive and the Honey Bee, Dadant & Sons, Inc., Hamilton, IL, 1975.
- PMID 23630255.
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- ^ Sanford, Malcolm T. "Producing Pollen". University of Florida, Institute of Food and Agricultural Sciences. Archived from the original on 2001-04-29. Retrieved 2007-08-30. Document ENY118. Original publication date November 1, 1994. Revised February 1, 1995. Reviewed May 1, 2003.
- ^ "Source". Aarongilbreath's Blog. 2013-05-31.
- ^ "How a Pollen Trap Works (Bee Pollen)". YouTube. Archived from the original on 2021-11-04.
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- ^ Bryant, Vaughn M. "Forensic Palynology: A New Way to Catch Crooks". crimeandclues.com. Archived from the original on 2007-02-03.
- ^ Stackhouse, Robert (17 April 2003). "Forensics studies look to pollen". The Battalion. Archived from the original on 2013-04-23.
- ^ Wood, Peter (9 September 2004). "Pollen helps war crime forensics". BBC News.
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Bibliography
- Simpson, Michael G. (2011). Plant Systematics. Academic Press. ISBN 978-0-08-051404-8. Retrieved 12 February 2014.
- Singh, Gurcharan (2004). Plant Systematics: An Integrated Approach. Science Publishers. ISBN 978-1-57808-351-0. Retrieved 23 January 2014.
- Furness, Carol A.; S2CID 83903452.
- "Pollen Grain Surface Pattern Terminology" (PDF). Quick Reference Glossary with Illustrations. Florida Institute of Technology: Center for Applied Biogeography. October 2014. Archived (PDF) from the original on 2019-08-11. Retrieved 11 August 2019.
- Society for the Promotion of Palynological Research in Austria (2021). "Illustrated Pollen Terms". PalDat - Palynological Database. University of Vienna. Division of Structural and Functional Botany. Retrieved 16 January 2021.
- Davis, Owen (1999). "Palynology — Pollen". University of Arizona. Department of Geosciences. Archived from the original on 2005-12-22. Retrieved 2009-02-19.
- Kaltenrieder, Petra; von Ballmoos, Peter (2003). "Types of Apertures in microspores". Introduction to pollen analysis. Institute of Plant Sciences, University of Bern. Retrieved 28 June 2021.
External links
- Pollen and 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 families)
- Pollen-Wiki - A digital Pollen-Atlas, retrieved 9 February 2018.
- YouTube video of pollen clouds from Juncus gerardii plants