Editing Halotolerance

{{Short description|Adaptation to high salinity}}
'''Halotolerance''' is the [[osmoregulation|adaptation]] of living [[organism]]s to conditions of high [[salinity]].<ref>Walter Larcher (2001) ''Physiological Plant Ecology''  {{ISBN|3-540-43516-6}}</ref> Halotolerant species tend to live in areas such as [[hypersaline lake]]s, [[dune|coastal dunes]], saline [[desert]]s, [[salt marsh]]es, and inland salt [[sea]]s and [[spring (hydrosphere)|spring]]s. [[Halophile]]s are also organisms that not only live in highly saline environments but also ''require'' the [[salinity]] to survive. Halotolerant organisms on the other hand (belonging to different [[Domain (biology)|domains]] of life) can grow under saline conditions, but do not require elevated concentrations of salt for growth. [[Halophyte]]s are salt-tolerant higher plants. Halotolerant microorganisms are of considerable biotechnological interest.<ref>{{Cite journal | doi = 10.1007/s007920100184 | last1 = Margesin | first1 = R. | last2 = Schinner | first2 = F. | title = Potential of halotolerant and halophilic microorganisms for biotechnology | journal = Extremophiles: Life Under Extreme Conditions | volume = 5 | issue = 2 | pages = 73–83 | year = 2001 | pmid = 11354458| s2cid = 22371046 }}</ref>

==Applications==
Fields of scientific research relevant to halotolerance include [[biochemistry]], [[molecular biology]], [[cell biology]], [[physiology]], [[ecology]], and [[genetics]].

An understanding of halotolerance can be applicable to areas such as [[arid-zone agriculture]], [[xeriscaping]], [[aquaculture]] (of fish or algae), bioproduction of desirable compounds (such as [[phycobiliprotein]]s or [[carotenoid]]s) using seawater to support growth, or [[Environmental remediation|remediation]] of salt-affected soils. In addition, many environmental stressors involve or induce osmotic changes, so knowledge gained about halotolerance can also be relevant to understanding tolerance to extremes in moisture or temperature.

Goals of studying halotolerance include increasing the agricultural productivity of lands affected by [[soil salination]] or where only saline water is available. Conventional agricultural species could be made more halotolerant by gene transfer from naturally halotolerant species (by conventional [[Artificial selection|breeding]] or [[genetic engineering]]) or by applying treatments developed from an understanding of the mechanisms of halotolerance. In addition, naturally halotolerant plants or microorganisms could be developed into useful [[agriculture|agricultural]] crops or [[fermentation (biochemistry)|fermentation]] organisms.

==Cellular functions in halophytes==
Tolerance of high salt conditions can be obtained through several routes. High levels of salt entering the plant can trigger ionic imbalances which cause complications in respiration and photosynthesis, leading to reduced rates of growth, injury and death in severe cases. To be considered tolerant of saline conditions, the [[protoplast]] must show methods of balancing the toxic and [[osmotic]] effects of the increased salt concentrations. Halophytic vascular plants can survive on soils with salt concentrations around 6%, or up to 20% in extreme cases ([[ocean salinity]] is around 3.5%). Tolerance of such conditions is reached through the use of [[stress proteins]] and compatible cytoplasm osmotic solutes.<ref name=Gupta-2014>{{cite journal| title=Mechanism of Salinity Tolerance in Plants: Physiological, Biochemical, and Molecular Characterization| first1=Bhaskar| last1=Gupta| first2=Bingru| last2=Huang| journal=[[International Journal of Genomics]]| volume=2014| pages=701596| doi=10.1155/2014/701596| pmid=24804192| pmc=3996477| date=3 April 2014| doi-access=free}}</ref>

To exist in such conditions, halophytes tend to be subject to the uptake of high levels of salt into their cells, and this is often required to maintain an osmotic potential lower than that of the soil to ensure water uptake. High salt concentrations within the cell can be damaging to sensitive organelles such as the chloroplast, so sequestration of salt is seen. Under this action, salt is stored within the [[vacuole]] to protect such delicate areas. If high salt concentrations are seen within the vacuole, a high concentration gradient will be established between the vacuole and the cytoplasm, leading to high levels of energy investment to maintain this state. Therefore, the accumulation of compatible cytoplasmic osmotic solutes can be seen to prevent this situation from occurring. [[Amino acid]]s such as proline accumulate in halophytic [[Brassica]] species, quaternary ammonium bases such as Glycine Betaine and sugars have been shown to act in this role within halophytic members of [[Chenopodiaceae]] and members of [[Asteraceae]] show the buildup of cyclites and soluble sugars. The buildup of these compounds allow for the balancing of the osmotic effect while preventing the establishment of toxic concentrations of salt or requiring the maintenance of high concentration gradients.{{Citation needed|date=January 2022}}

==Bacterial halotolerance==
The extent of halotolerance varies widely amongst different species of bacteria.<ref>Dieter Häussinger and Helmut Sies (2007) ''Osmosensing and Osmosignaling'', Academic Press, 579 pages  {{ISBN|0-12-373921-7}}</ref> A number of [[cyanobacteria]] are halotolerant; an example location of occurrence for such cyanobacteria is in the [[Makgadikgadi Pans]], a large [[hypersaline lake]] in [[Botswana]].<ref>C. Michael Hogan (2008) [http://www.megalithic.co.uk/article.php?sid=22373&mode=&order=0''Makgadikgadi'', The Megalithic Portal, ed. A. Burnham]</ref>

==Fungal halotolerance==
[[Fungi]] from habitats with high concentration of salt are mostly halotolerant (i.e. they do not require salt for growth) and not halophilic. Halophilic fungi are a rare exception.<ref>{{Cite journal 
| last1 = Gostinčar | first1 = C. 
| last2 = Grube | first2 = M. 
| last3 = De Hoog | first3 = S. 
| last4 = Zalar | first4 = P. 
| last5 = Gunde-Cimerman | first5 = N. 
| title = Extremotolerance in fungi: Evolution on the edge 
| doi = 10.1111/j.1574-6941.2009.00794.x 
| journal = FEMS Microbiology Ecology 
| volume = 71 
| issue = 1 
| pages = 2–11 
| year = 2010 
| pmid = 19878320 
| doi-access = free 
}}</ref> Halotolerant fungi constitute a relatively large and constant part of hypersaline environment communities, such as those in the [[Saltern|solar salterns]].<ref>{{Cite book | last1 = Zajc | first1 = J. | last2 = Zalar | first2 = P. | last3 = Plemenitaš | first3 = A. | last4 = Gunde-Cimerman | first4 = N. | doi = 10.1007/978-3-642-23342-5_7 | chapter = The Mycobiota of the Salterns | title = Biology of Marine Fungi | series = Progress in Molecular and Subcellular Biology | volume = 53 | pages = 133–158 | year = 2012 | isbn = 978-3-642-23341-8 | pmid = 22222830 }}</ref> Well studied examples include the yeast ''[[Debaryomyces hansenii]] ''and [[black yeast]]s ''[[Aureobasidium pullulans]]'' and ''[[Hortaea werneckii]]''.<ref>{{Cite journal | last1 = Gunde-Cimerman | first1 = N. | last2 = Ramos | first2 = J. | last3 = Plemenitaš | first3 = A. | doi = 10.1016/j.mycres.2009.09.002 | title = Halotolerant and halophilic fungi | journal = Mycological Research | volume = 113 | issue = 11 | pages = 1231–1241 | year = 2009 | pmid = 19747974 }}</ref> The latter can grow in media without salt, as well as in almost saturated [[NaCl]] solutions. To emphasize this unusually wide [[adaptability]], some authors describe ''H. werneckii ''as "extremely halotolerant".<ref>{{Cite book | last1 = Gostinčar | first1 = C. | last2 = Lenassi | first2 = M. | last3 = Gunde-Cimerman | first3 = N. | last4 = Plemenitaš | first4 = A. | title = Fungal Adaptation to Extremely High Salt Concentrations | doi = 10.1016/B978-0-12-387044-5.00003-0 | series = Advances in Applied Microbiology | volume = 77 | pages = 71–96 | year = 2011 | isbn = 9780123870445 | pmid = 22050822 }}</ref>

== See also ==

* {{annotated link|Arabidopsis thaliana responses to salinity|''Arabidopsis thaliana'' responses to salinity}}
* {{annotated link|Biosalinity}}
* {{annotated link|Crop tolerance to seawater}}
* {{annotated link|Salinity control}}
* {{annotated link|Salt tolerance of crops}}
* {{annotated link|Sodium in biology}}
* {{annotated link|Soil salinity}}
* {{annotated link|Soil salinity control}}

==References==
{{reflist}}

{{Animalosmo}}

[[Category:Environmental microbiology]]
[[Category:Geomicrobiology]]
[[Category:Microbial growth and nutrition]]

[[de:Halophil]]