View source for Tropism

{{Short description|Directed growth of an organism in response to environmental stimuli}}
{{About|physical movement in organisms|infection specificity of pathogens|Host tropism|and|Tissue tropism|the novel|Tropisms}}
{{More citations needed|date=September 2012}}
[[File:Bellis perennis - Gaenseblume4.jpg|thumb|300px|Daisies (''[[Bellis perennis]]'') facing the Sun after opening in the morning showing [[heliotropism]]]]
[[File:Phycomyces3.JPG|thumb|''[[Phycomyces]]'', a fungus, exhibiting phototropism]]

In [[biology]], a '''tropism''' is a [[phenomenon]] indicating the growth or turning movement of an [[organism]], usually a [[plant]], in response to an environmental [[stimulus (physiology)|stimulus]].<ref>{{Cite book |last=Darwin |first=Charles |url=https://books.google.com/books?id=g3BKAAAAMAAJ |title=The Power of Movement in Plants |date=1900 |publisher=Appleton |language=en}}</ref> In tropisms, this response is dependent on the direction of the stimulus (as opposed to [[nastic movements]], which are non-directional responses). Tropisms are usually named for the stimulus involved; for example, a [[phototropism]] is a movement to the light source, and an anemotropism is the response and [[adaptation]] of plants to the wind.<ref>{{Cite web |last=Taki |first=Tarek Siddiki |date=2023-09-30 |title=Anemotropism: Plants Response & Adaptation To Wind |url=https://greenleen.com/anemotropism-plants-response-adaptation-to-wind/ |access-date=2023-09-30 |website=GreenLeen.Com |language=en-US}}</ref>

Tropisms occur in three sequential steps. First, there is a sensation to a stimulus. Next, [[signal transduction]] occurs. And finally, the directional growth response occurs.

Tropisms can be regarded by [[Ethology|ethologists]] as  ''[[taxis]]'' (directional response) or  ''[[kinesis (biology)|kinesis]]'' (non-directional response).

The [[Cholodny–Went model]], proposed in 1927, is an early model describing tropism in emerging shoots of [[monocotyledon]]s, including the tendencies for the stalk to grow towards light (phototropism) and the roots to grow downward ([[gravitropism]]).
In both cases, the directional growth is considered to be due to asymmetrical distribution of [[auxin]], a plant growth [[hormone]].<ref name="Plant Cell" />

{{anchor |Viruses}}The term "tropism" ({{ety|grc|''{{wikt-lang|grc|τρόπος}}'' ({{grc-transl|τρόπος}})|a turn, way, manner, style, etc.||[[-ism]]}}) is also used in unrelated contexts. [[Virus]]es and other pathogens affect what is called "[[host tropism]]", "[[tissue tropism]]", or "cell tropism"; in which case tropism refers to the way in which different viruses/pathogens have evolved to preferentially target specific host species, specific tissue, or specific cell types within those species. In English, the word ''tropism'' is also used to indicate an action done without cognitive thought: However, "tropism" in this sense has a proper, although non-scientific, meaning as an [[Instinct|innate tendency]], natural inclination, or propensity to act in a certain manner towards a certain stimulus.

== Types ==
Tropisms can be distinguished according to the orientation with respect to the direction of the stimulus. They can commonly be either ''positive'' (towards the stimulus) or ''negative'' (away from it).<ref name=":0">{{Cite web |title=Plant tropisms - Plant and animal hormones |url=https://www.bbc.co.uk/bitesize/guides/z98p34j/revision/3 |archive-url=https://web.archive.org/web/20220121121129/https://www.bbc.co.uk/bitesize/guides/z98p34j/revision/3 |url-status=dead |archive-date=January 21, 2022 |access-date=22 April 2022 |website=[[BBC Bitesize]]}}</ref> Both of these are ''orthotropic'',<ref>{{cite OED|orthotropic|access-date=2 July 2022}}</ref> and can be contrasted with tropisms that are ''diatropic'' (perpendicular to the stimulus) or ''plagiotropic'' (at an oblique angle).<ref name=":1">{{Cite web |date=2003 |title=Tropism {{!}} biology |url=https://www.britannica.com/science/tropism |access-date=2 July 2022 |website=[[Encyclopædia Britannica Online]]}}</ref>

According to the type of stimulus, tropisms can be:
[[File:Upsidedown-tree.JPG|thumb|Example of gravitropism in the remains of a cellar of a Roman villa in the Archeologic Park in [[Baiae|Baia, Italy]]]]
* [[Aerotropism]]: the growth of plants towards or away from a source of [[wind]]<ref>{{Cite web |title=Aerotropism |url=https://www.merriam-webster.com/medical/aerotropism |access-date=22 April 2022 |website=[[Merriam Webster]]}}</ref>
* [[Chemotropism]]: the movement or growth in response to [[chemical]]s<ref>{{Cite web |title=Chemotropism |url=https://www.merriam-webster.com/dictionary/chemotropism |access-date=22 April 2022 |website=[[Merriam Webster]]}}</ref>
* [[Electrotropism]], or galvanotropism: the movement or growth in response to an [[electric field]]<ref name=":1" /><ref>{{Cite web |title=Galvanonism |url=https://www.merriam-webster.com/medical/galvanotropism |access-date=22 April 2022 |website=[[Merriam Webster]]}}</ref>
* Exotropism: continuation of growth "outward," i.e. in the previously established direction<ref>{{Cite web |title=Exotropism |url=https://www.merriam-webster.com/dictionary/exotropism |access-date=22 April 2022 |website=[[Merriam Webster]]}}</ref>
* [[Gravitropism]] (sometimes referred to as geotropism): is movement or growth in response to [[gravity]]<ref name=":0" />
** Apogeotropism: negative geotropism
* [[Heliotropism]]: the diurnal motion or seasonal motion of plant parts in response to the direction of the Sun, (e.g. the [[sunflower]])
** Apheliotropism: negative heliotropism
* [[Hydrotropism]]: movement or growth in response to [[water]]; in plants, the root cap senses differences in water moisture in the soil, and signals cellular changes that cause the root to curve towards the area of higher moisture<ref>{{Cite journal|last1=Cassab|first1=Gladys I.|last2=Eapen|first2=Delfeena|last3=Campos|first3=María Eugenia|date=2013-01-01|title=Root hydrotropism: An update|journal=American Journal of Botany|language=en|volume=100|issue=1|pages=14–24|doi=10.3732/ajb.1200306|issn=0002-9122|pmid=23258371}}</ref>
** Prohydrotropism: positive hydrotropism
* Hygrotropism: movement or growth in response to moisture or humidity{{citation needed|date=April 2022}}
* [[Inotrope|Inotropism]]: muscular contraction in response to drugs
* [[Magnetotropism]]: movement or growth in response to magnetic fields
* [[Phototropism]]: movement or growth in response to [[light]]s or [[color spectrum|colors of light]]
** Aphototropism: negative phototropism
** Skototropism: negative phototropism of vines
* Selenotropism: motion of plant parts in response to the direction of the Moon<ref>{{Cite web |title=Selenotropism definition and meaning |url=https://www.collinsdictionary.com/dictionary/english/selenotropism |access-date=24 April 2022 |website=[[Collins Dictionary]]}}</ref>
* [[Thermotropism]]: movement or growth in response to [[temperature]]
* [[Thigmotropism]]: movement or growth in response to [[somatic sensation|touch]] or contact
* Traumatotropism: orientation deviation after suffering a wounding<ref name=":1" /><ref>{{Cite web |title=Traumatropism |url=https://www.merriam-webster.com/dictionary/traumatropism |access-date=24 April 2022 |website=[[Merriam Webster]]}}</ref>

== See also ==
* [[Chemotaxis]]
* [[Rapid plant movement]]
* [[Nutation (botany)]]

== References ==
{{reflist
| refs =
<ref name="Plant Cell">
{{cite journal
|author1=Haga, Ken |author2=Takano, Makoto |author3=Neumann, Ralf |author4=Iino, Moritoshi | date = January 1, 2005
| title = The Rice COLEOPTILE PHOTOTROPISM1 Gene Encoding an Ortholog of Arabidopsis NPH3 Is Required for Phototropism of Coleoptiles and Lateral Translocation of Auxin(W)
| journal = Plant Cell
| url = http://www.plantcell.org/content/17/1/103.full
| doi = 10.1105/tpc.104.028357
|pmc=544493 | pmid=15598797 | volume=17 |issue=1 | pages=103–15}} 
</ref>
}}

== External links ==
* {{Wiktionary inline}}
* {{Commons category-inline|Tropism}}

{{Tropism}}
{{Authority control}}

[[Category:Tropism| ]]