Mucilage

Mucilage is a thick gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion. The direction of their movement is always opposite to that of the secretion of mucilage.[1] It is a polar glycoprotein and an exopolysaccharide. Mucilage in plants plays a role in the storage of water and food, seed germination, and thickening membranes. Cacti (and other succulents) and flax seeds are especially rich sources of mucilage.[2]

A sundew with a leaf bent around a fly trapped by mucilage

Not to be confused with mucigel.

Occurrence

Exopolysaccharides are the most stabilising factor for microaggregates and are widely distributed in soils. Therefore, exopolysaccharide-producing "soil algae" play a vital role in the ecology of the world's soils. The substance covers the outside of, for example, unicellular or filamentous green algae and cyanobacteria. Amongst the green algae especially, the group Volvocales are known to produce exopolysaccharides at a certain point in their life cycle. It occurs in almost all plants, but usually in small amounts. It is frequently associated with substances like tannins and alkaloids.[3]

Mucilage has a unique purpose in some carnivorous plants. The plant genera Drosera (sundews), Pinguicula, and others have leaves studded with mucilage-secreting glands, and use a "flypaper trap" to capture insects.[4]

Human uses
Glass container for mucilage, from the first half of the 20th century

Mucilage is edible. It is used in medicine as it relieves irritation of mucous membranes by forming a protective film. It is known to act as a soluble, or viscous, dietary fiber that thickens the fecal mass, an example being the consumption of fiber supplements containing psyllium seed husks.[5]

Traditionally, marshmallows were made from the extract of the mucilaginous root of the marshmallow plant (Althaea officinalis). The inner bark of the slippery elm (Ulmus rubra), a North American tree species, has long been used as a demulcent and cough medicine, and is still produced commercially for that purpose.[6]

Mucilage mixed with water has been used as a glue, especially for bonding paper items such as labels, postage stamps, and envelope flaps.[7] Differing types and varying strengths of mucilage can also be used for other adhesive applications, including gluing labels to metal cans, wood to china, and leather to pasteboard.[8] During the fermentation of nattō soybeans, extracellular enzymes produced by the bacterium Bacillus natto react with soybean sugars to produce mucilage. The amount and viscosity of the mucilage are important nattō characteristics, contributing to nattō's unique taste and smell.

The mucilage of two kinds of insectivorous plants, sundew (Drosera)[9] and butterwort (Pinguicula),[10] is used for the traditional production of a variant of the yogurt-like Swedish dairy product called filmjölk.[11][12]

Ecological implications for plants

The presence of mucilage in seeds affects important ecological processes in some plant species, such as tolerance of water stress, competition via allelopathy, or facilitation of germination through attachment to soil particles.[13][14][15] Some authors have also suggested a role of seed mucilage in protecting DNA material from irradiation damage.[16] The amount of mucilage produced per seed has been shown to vary across the distribution range of a species, in relation with local environmental conditions of the populations.[17]

A variety of maize grows aerial roots that produce a sweet mucus. The Sierra Mixe is a tall variety that survives in poor soils without fertilizer in Oaxaca, Mexico, and the mucilage has been shown to support nitrogen fixation through bacteria that thrive in its high-sugar, low-oxygen environment.[18]

Plant sources

The following plant and algae species are known to contain far greater concentrations of mucilage than typical:

See also
  • Marine mucilage, also known as sea snot – Type of organic matter found in the sea

References
  1. "Modes of Locomotion in Protists: 5 Modes". Biology Discussion. 6 September 2016. Archived from the original on 24 December 2017. Retrieved 26 October 2017.
  2. "Mucilage cell, cactus". www.sbs.utexas.edu. Archived from the original on 15 June 2017. Retrieved 26 October 2017.
  3. Paul, Eldon A., ed. (2006). Soil Microbiology, Ecology and Biochemistry (3rd ed.). Academic Press. p. 33. ISBN 9780080475141. Archived from the original on 24 December 2017.
  4. "Carnivorous Plant Trapping Mechanisms". International Carnivorous Plant Society. Archived from the original on 6 April 2016. Retrieved 29 March 2016.
  5. Institute of Medicine (2001). Dietary Reference Intakes: Proposed Definition of Dietary Fiber. Washington, D.C.: National Academy Press. p. 19. ISBN 978-0-309-07564-0.
  6. "Slippery Elm". University of Maryland Medical Center. Archived from the original on 17 November 2015.
  7. Spitzenberger, Ray (23 August 2007). "Glue, Paste or Mucilage: Know the Difference?". East Bernard Express. East Bernard, TX. Retrieved 29 March 2016.
  8. Dawidowsky, Ferdinand (1905). Glue, Gelatine, Animal Charcoal, Phosphorus, Cements, Pastes, and Mucilage. Henry Carey Baird & Co. p. 1. ISBN 978-1-113-00611-0.
  9. "Drosera L." Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 16 March 2023.
  10. "Filmjölk från Linnés tid" (PDF). Verumjournalen (in Swedish). 2002: 10. 2002. Retrieved 18 July 2007.
  11. Östman, Elisabeth (1911). "Recept på filmjölk, filbunke och långmjölk". Iduns kokbok (in Swedish). Stockholm: Aktiebolaget Ljus, Isaac Marcus' Boktryckeriaktiebolag. p. 161. Archived from the original on 29 October 2008. Retrieved 18 July 2007.
  12. "Vad gjorde man med mjölken?" (in Swedish). Järnriket Gästrikland, Länsmuseet Gävleborg. Archived from the original on 22 March 2007. Retrieved 5 August 2007.
  13. Harper, J. L.; Benton, R. A. (1 January 1966). "The Behaviour of Seeds in Soil: II. The Germination of Seeds on the Surface of a Water Supplying Substrate". Journal of Ecology. 54 (1): 151–166. doi:10.2307/2257664. JSTOR 2257664.
  14. Hasegawa, K.; Mizutani, J.; Kosemura, S.; Yamamura, S. (1 October 1992). "Isolation and identification of lepidimoide, a new allelopathic substance from mucilage of germinated cress seeds". Plant Physiology. 100 (2): 1059–1061. doi:10.1104/pp.100.2.1059. ISSN 0032-0889. PMC 1075667. PMID 16653018.
  15. Lu, Juanjuan; Tan, Dunyan; Baskin, Jerry M.; Baskin, Carol C. (1 June 2010). "Fruit and seed heteromorphism in the cold desert annual ephemeral Diptychocarpus strictus (Brassicaceae) and possible adaptive significance". Annals of Botany. 105 (6): 999–1014. doi:10.1093/aob/mcq041. ISSN 0305-7364. PMC 2876001. PMID 20348559.
  16. Yang, Xuejun; Zhang, Wenhao; Dong, Ming; Boubriak, Ivan; Huang, Zhenying (2 September 2011). "The Achene Mucilage Hydrated in Desert Dew Assists Seed Cells in Maintaining DNA Integrity: Adaptive Strategy of Desert Plant Artemisia sphaerocephala". PLOS ONE. 6 (9): e24346. Bibcode:2011PLoSO...624346Y. doi:10.1371/journal.pone.0024346. ISSN 1932-6203. PMC 3166310. PMID 21912689.
  17. Villellas, J.; García, M. B. (1 September 2013). "The role of the tolerance–fecundity trade-off in maintaining intraspecific seed trait variation in a widespread dimorphic herb" (PDF). Plant Biology. 15 (5): 899–909. doi:10.1111/j.1438-8677.2012.00684.x. hdl:10261/87756. ISSN 1438-8677. PMID 23126286.
  18. Daley, Jason (10 August 2018). "The Corn of the Future Is Hundreds of Years Old and Makes Its Own Mucus". Smithsonian Magazine. ISSN 0037-7333.
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