Editing Abiotic stress (section)

==In plants==
A plant's first line of defense against abiotic stress is in its roots.  If the soil holding the plant is healthy and biologically diverse, the plant will have a higher chance of surviving stressful conditions.<ref name="bruss"/>

The plant responses to stress are dependent on the tissue or organ affected by the stress.<ref name=":2" /> For example, transcriptional responses to stress are tissue or cell specific in roots and are quite different depending on the stress involved.<ref>{{Cite journal|last1=Cramer|first1=Grant R|last2=Urano|first2=Kaoru|last3=Delrot|first3=Serge|last4=Pezzotti|first4=Mario|last5=Shinozaki|first5=Kazuo|date=2011-11-17|title=Effects of abiotic stress on plants: a systems biology perspective|journal=BMC Plant Biology|volume=11|pages=163|doi=10.1186/1471-2229-11-163 |doi-access=free|issn=1471-2229|pmc=3252258|pmid=22094046}}</ref>

One of the primary responses to abiotic stress such as high salinity is the disruption of the Na+/K+ ratio in the cytoplasm of the plant cell.  High concentrations of Na+, for example, can decrease the capacity for the plant to take up water and also alter enzyme and transporter functions.  Evolved adaptations to efficiently restore cellular ion homeostasis have led to a wide variety of stress tolerant plants.<ref>{{Cite journal|last=Conde|first=Artur|year=2011|title=Membrane Transport, Sensing and Signaling in Plant Adaptation to Environmental Stress|url=http://oup.silverchair-cdn.com/oup/backfile/Content_public/Journal/pcp/52/9/10.1093/pcp/pcr107/2/pcr107.pdf?Expires=1485797994&Signature=Cemd6gLc-NOAT39G3-6uNqRUU6r97KGEAOyCNNn2uYjNVPelfxGYMUDxK660bIU6Afj6fNwTfB9pXf9DgOcCqz5CJOjC-bL3H19H1eFUe0Wsid8jnH9J4k30SaaF-arCEmbLrBsTJrWkrsq84THqi0ervfu-4hd~5arrd-ytItFSqkXje1frT3zWxJoosf3~Asfs-5qt50yGImSOXHjVk2LNgZeyD5FKqt7KZReojKLjZnZIUsdHLnDBD4RjF24ezB3mbbNtz8kq60eoiVUFMWlJhkYoD7NYwijrartby2612WMmS1vkKnZ3bT5emRl9qe8trQJarCUlQEKUYp6MDA__&Key-Pair-Id=APKAIUCZBIA4LVPAVW3Q|journal=Plant & Cell Physiology|volume=52 | issue = 9 |pages=1583–1602|via=Google Scholar|doi=10.1093/pcp/pcr107|pmid=21828102|doi-access=free}}</ref>

Facilitation, or the positive interactions between different species of plants, is an intricate web of association in a natural environment.  It is how plants work together.  In areas of high stress, the level of facilitation is especially high as well.  This could possibly be because the plants need a stronger network to survive in a harsher environment, so their interactions between species, such as cross-pollination or mutualistic actions, become more common to cope with the severity of their habitat.<ref>{{cite journal | last1 = Maestre | first1 = Fernando T. | last2 = Cortina | first2 = Jordi | last3 = Bautista | first3 = Susana | year = 2007 | title = Mechanisms underlying the interaction between Pinus halepensis and the native late-successional shrub Pistacia lentiscus in a semi-arid plantation | doi = 10.1111/j.0906-7590.2004.03990.x | journal = Ecography | volume = 27 | issue = 6| pages = 776–786 }}</ref>

Plants also adapt very differently from one another, even from a plant living in the same area.  When a group of different plant species was prompted by a variety of different stress signals, such as drought or cold, each plant responded uniquely.  Hardly any of the responses were similar, even though the plants had become accustomed to exactly the same home environment.<ref name ="mitt"/>
[[File:Sunflowers in fields.jpg|thumb|Sunflowers are hyperaccumulator plants that can absorb large amount of metal.]]
Serpentine soils (media with low concentrations of nutrients and high concentrations of heavy metals) can be a source of abiotic stress. Initially, the absorption of toxic metal ions is limited by cell membrane exclusion. Ions that are absorbed into tissues are sequestered in cell vacuoles. This sequestration mechanism is facilitated by proteins on the vacuole membrane.<ref>{{Cite journal|author1=Palm, Brady |author2=Van Volkenburgh|date=2012|title=Serpentine tolerance in Mimuslus guttatus does not rely on exclusion of magnesium|journal=Functional Plant Biology|volume=39|issue=8|pages=679–688|doi=10.1071/FP12059|pmid=32480819}}</ref> An example of plants that adapt to serpentine soil are Metallophytes, or hyperaccumulators, as they are known for their ability to absorbed heavy metals using the root-to-shoot translocation (which it will absorb into shoots rather than the plant itself). They're also extinguished for their ability to absorb toxic substances from heavy metals.<ref>{{Cite journal|last1=Singh|first1=Samiksha|last2=Parihar|first2=Parul|last3=Singh|first3=Rachana|last4=Singh|first4=Vijay P.|last5=Prasad|first5=Sheo M.|date=2016|title=Heavy Metal Tolerance in Plants: Role of Transcriptomics, Proteomics, Metabolomics, and Ionomics|journal=Frontiers in Plant Science|language=en|volume=6|page=1143|doi=10.3389/fpls.2015.01143 |pmid=26904030|pmc=4744854|issn=1664-462X|doi-access=free}}</ref>

Chemical priming has been proposed to increase tolerance to abiotic stresses in crop plants. In this method, which is analogous to vaccination, stress-inducing chemical agents are introduced to the plant in brief doses so that the plant begins preparing defense mechanisms. Thus, when the abiotic stress occurs, the plant has already prepared defense mechanisms that can be activated faster and increase tolerance.<ref>{{Cite journal|last=Savvides|first=Andreas|date=December 15, 2015|title=Chemical Priming of Plants Against Multiple Abiotic Stresses: Mission Possible?|url=http://www.cell.com/trends/plant-science/abstract/S1360-1385(15)00283-6|journal=Trends in Plant Science|volume=21|issue=4|pages=329–340|doi=10.1016/j.tplants.2015.11.003|pmid=26704665|access-date=March 10, 2016|hdl=10754/596020|hdl-access=free}}</ref> Prior exposure to tolerable doses of biotic stresses such as phloem-feeding insect infestation have also been shown to increase tolerance to abiotic stresses in plant<ref>{{cite journal |last1=Sulaiman |first1=Hassan Y. |last2=Liu |first2=Bin |last3=Kaurilind |first3=Eve |last4=Niinemets |first4=Ülo |title=Phloem-feeding insect infestation antagonizes volatile organic compound emissions and enhances heat stress recovery of photosynthesis in Origanum vulgare |journal=Environmental and Experimental Botany |date=1 September 2021 |volume=189 |pages=104551 |doi=10.1016/j.envexpbot.2021.104551 |bibcode=2021EnvEB.18904551S |url=https://www.sciencedirect.com/science/article/pii/S0098847221001817 |access-date=7 October 2021 |language=en |issn=0098-8472}}</ref>

===Impact on food production===

Abiotic stress mostly affects plants used in agriculture. Some examples of adverse conditions (which may be caused by [[climate change]]) are high or low temperatures, drought, [[salinity]], and toxins.<ref>{{Cite journal|last1=Gull|first1=Audil|last2=Lone|first2=Ajaz Ahmad|last3=Wani|first3=Noor Ul Islam|date=2019-10-07|title=Biotic and Abiotic Stresses in Plants|url=https://www.intechopen.com/books/abiotic-and-biotic-stress-in-plants/biotic-and-abiotic-stresses-in-plants|journal=Abiotic and Biotic Stress in Plants|language=en|doi=10.5772/intechopen.85832|isbn=978-1-78923-811-2|doi-access=free}}</ref>

* Rice (''[[Oryza sativa]]'') is a classic example. Rice is a staple food throughout the world, especially in China and India. Rice plants can undergo different types of abiotic stresses, like drought and high salinity. These stress conditions adversely affect rice production. Genetic diversity has been studied among several rice varieties with different genotypes, using molecular markers.<ref name=":03">{{Cite journal|last1=Yadav|first1=Summy|last2=Modi|first2=Payal|last3=Dave|first3=Akanksha|last4=Vijapura|first4=Akdasbanu|last5=Patel|first5=Disha|last6=Patel|first6=Mohini|date=2020-06-17|title=Effect of Abiotic Stress on Crops|url=https://www.intechopen.com/books/sustainable-crop-production/effect-of-abiotic-stress-on-crops|journal=Sustainable Crop Production|language=en|doi=10.5772/intechopen.88434|isbn=978-1-78985-317-9|doi-access=free}}</ref>
* Chickpea production is affected by drought. Chickpeas are one of the most important foods in the world.<ref name=":03" />
* Wheat is another major crop that is affected by drought: lack of water affects the plant development, and can wither the leaves.<ref name=":03" /><ref name="S. Sarkar">{{cite journal |last1=Sarkar |first1=S. |last2=Islam |first2=A.K.M.Aminul |last3=Barma |first3=N.C.D |last4=Ahmed |first4=J.U. |title=Tolerance mechanisms for breeding wheat against heat stress: A review |journal=South African Journal of Botany |date=May 2021 |volume=138 |page=262-277 |doi=10.1016/j.sajb.2021.01.003|doi-access=free }}</ref>
* Maize crops can be affected by high temperature and drought, leading to the loss of maize crops due to poor plant development.<ref name=":03" />
* [[Soybean]] is a major source of protein, and its production is also affected by drought.<ref name=":03" />

=== Salt stress in plants ===
Soil salinization, the accumulation of water-soluble salts to levels that negatively impact plant production, is a global phenomenon affecting approximately 831 million hectares of land.<ref>Martinez-Beltran J, Manzur CL. (2005). Overview of salinity problems in the world and FAO strategies to address the problem. Proceedings of the international salinity forum, Riverside, California, April 2005, 311–313.</ref> More specifically, the phenomenon threatens 19.5% of the world's irrigated agricultural land and 2.1% of the world's non-irrigated (dry-land) agricultural lands.<ref name=":0">{{Cite journal|last1=Neto|first1=Azevedo|last2=De|first2=André Dias|last3=Prisco|first3=José Tarquinio|last4=Enéas-Filho|first4=Joaquim|last5=Lacerda|first5=Claudivan Feitosa de|last6=Silva|first6=José Vieira|last7=Costa|first7=Paulo Henrique Alves da|last8=Gomes-Filho|first8=Enéas|date=2004-04-01|title=Effects of salt stress on plant growth, stomatal response and solute accumulation of different maize genotypes|journal=Brazilian Journal of Plant Physiology|volume=16|issue=1|pages=31–38|doi=10.1590/S1677-04202004000100005|issn=1677-0420|doi-access=free}}</ref> High [[soil salinity]] content can be harmful to plants because water-soluble salts can alter osmotic potential gradients and consequently inhibit many cellular functions.<ref name=":0" /><ref>Zhu, J.-K. (2001). Plant Salt Stress. eLS.</ref> For example, high soil salinity content can inhibit the process of photosynthesis by limiting a plant's water uptake; high levels of water-soluble salts in the soil can decrease the osmotic potential of the soil and consequently decrease the difference in water potential between the soil and the plant's roots, thereby limiting electron flow from H<sub>2</sub>O to P680 in [[Photosystem II|Photosystem II's]] reaction center.<ref>Lu. Congming, A. Vonshak. (2002). Effects of salinity stress on photosystem II function in cyanobacterial Spirulina platensis cells. Physiol. Plant 114 405-413.</ref>

Over generations, many plants have mutated and built different mechanisms to counter salinity effects.<ref name=":0" /> A good combatant of salinity in plants is the hormone [[ethylene]]. Ethylene is known for regulating plant growth and development and dealing with stress conditions. Many central membrane proteins in plants, such as ETO2, ERS1 and EIN2, are used for ethylene signaling in many plant growth processes. Mutations in these proteins can lead to heightened salt sensitivity and can limit plant growth. The effects of salinity has been studied on ''[[Arabidopsis]]'' plants that have mutated ERS1, ERS2, ETR1, ETR2 and EIN4 proteins. These proteins are used for ethylene signaling against certain stress conditions, such as salt and the ethylene precursor ACC is used to suppress any sensitivity to the salt stress.<ref>{{Cite journal|last1=Lei|first1=Gang|last2=Shen|first2=Ming|last3=Li|first3=Zhi-Gang|last4=Zhang|first4=Bo|last5=Duan|first5=Kai-Xuan|last6=Wang|first6=Ning|last7=Cao|first7=Yang-Rong|last8=Zhang|first8=Wan-Ke|last9=Ma|first9=Biao|date=2011-10-01|title=EIN2 regulates salt stress response and interacts with a MA3 domain-containing protein ECIP1 in Arabidopsis|journal=Plant, Cell & Environment|language=en|volume=34|issue=10|pages=1678–1692|doi=10.1111/j.1365-3040.2011.02363.x|pmid=21631530|issn=1365-3040|doi-access=free|bibcode=2011PCEnv..34.1678L }}</ref>

=== Phosphate starvation in plants ===

Phosphorus (P) is an essential macronutrient required for plant growth and development, but it is present only in limited quantities in most of the world's soil. Plants use P mainly in the form of soluble inorganic phosphates (PO<sub>4</sub><sup>−−−</sup>) but are subject to abiotic stress when there is not enough soluble PO<sub>4</sub><sup>−−−</sup> in the soil. Phosphorus forms insoluble complexes with Ca and Mg in alkaline soils and with Al and Fe in acidic soils that make the phosphorus unavailable for plant roots. When there is limited bioavailable P in the soil, plants show extensive symptoms of abiotic stress, such as short primary roots and more lateral roots and root hairs to make more surface available for phosphate absorption, exudation of organic acids and phosphatase to release phosphates from complex P–containing molecules and make it available for growing plants' organs.<ref>{{Cite journal|last=Raghothama|first=K. G.|date=1999-01-01|title=Phosphate Acquisition|journal=Annual Review of Plant Physiology and Plant Molecular Biology|volume=50|issue=1|pages=665–693|doi=10.1146/annurev.arplant.50.1.665|pmid=15012223}}</ref> It has been shown that PHR1, a [[MYB (gene)|MYB]]-related [[transcription factor]], is a master regulator of P-starvation response in plants.<ref>{{Cite journal|last1=Rubio|first1=Vicente|last2=Linhares|first2=Francisco|last3=Solano|first3=Roberto|last4=Martín|first4=Ana C.|last5=Iglesias|first5=Joaquín|last6=Leyva|first6=Antonio|last7=Paz-Ares|first7=Javier|date=2001-08-15|title=A conserved MYB transcription factor involved in phosphate starvation signaling both in vascular plants and in unicellular algae|journal=Genes & Development|language=en|volume=15|issue=16|pages=2122–2133|doi=10.1101/gad.204401|issn=0890-9369|pmc=312755|pmid=11511543}}</ref><ref name="Pant 1907–1918">{{Cite journal|last1=Pant|first1=Bikram Datt|last2=Burgos|first2=Asdrubal|last3=Pant|first3=Pooja|last4=Cuadros-Inostroza|first4=Alvaro|last5=Willmitzer|first5=Lothar|last6=Scheible|first6=Wolf-Rüdiger|date=2015-04-01|title=The transcription factor PHR1 regulates lipid remodeling and triacylglycerol accumulation in Arabidopsis thaliana during phosphorus starvation|url= |journal=Journal of Experimental Botany|language=en|volume=66|issue=7|pages=1907–1918|doi=10.1093/jxb/eru535|issn=0022-0957|pmc=4378627|pmid=25680792}}</ref> PHR1 also has been shown to regulate extensive remodeling of [[lipid]]s and [[metabolite]]s during phosphorus limitation stress<ref name="Pant 1907–1918"/><ref>{{Cite journal|last1=Pant|first1=Bikram-Datt|last2=Pant|first2=Pooja|last3=Erban|first3=Alexander|last4=Huhman|first4=David|last5=Kopka|first5=Joachim|last6=Scheible|first6=Wolf-Rüdiger|date=2015-01-01|title=Identification of primary and secondary metabolites with phosphorus status-dependent abundance in Arabidopsis, and of the transcription factor PHR1 as a major regulator of metabolic changes during phosphorus limitation|journal=Plant, Cell & Environment|language=en|volume=38|issue=1|pages=172–187|doi=10.1111/pce.12378|pmid=24894834|issn=1365-3040|doi-access=|bibcode=2015PCEnv..38..172P }}</ref>

=== Drought stress ===
Drought stress, defined as naturally occurring water deficit, is a main cause of crop losses in agriculture. This is because water is essential for many fundamental processes in plant growth.<ref name=":02">{{Cite journal|last1=González-Villagra|first1=Jorge|last2=Rodrigues-Salvador|first2=Acácio|last3=Nunes-Nesi|first3=Adriano|last4=Cohen|first4=Jerry D.|last5=Reyes-Díaz|first5=Marjorie M.|date=March 2018|title=Age-related mechanism and its relationship with secondary metabolism and abscisic acid in Aristotelia chilensis plants subjected to drought stress|journal=Plant Physiology and Biochemistry|volume=124|pages=136–145|doi=10.1016/j.plaphy.2018.01.010|pmid=29360623|issn=0981-9428|url=http://www.locus.ufv.br/handle/123456789/19426|doi-access=free|bibcode=2018PlPB..124..136G }}</ref> It has become especially important in recent years to find a way to combat drought stress. A decrease in precipitation and consequent increase in drought are extremely likely in the future due to an increase in global warming.<ref name=":1"/> Plants have come up with many mechanisms and adaptations to try and deal with drought stress. One of the leading ways that plants combat drought stress is by closing their [[stoma]]ta. A key hormone regulating stomatal opening and closing is [[abscisic acid]] (ABA). Synthesis of ABA causes the ABA to bind to receptors. This binding then affects the opening of ion channels, thereby decreasing [[turgor pressure]] in the stomata and causing them to close. Recent studies by Gonzalez-Villagra, et al., have shown how ABA levels increased in drought-stressed plants (2018). They showed that when plants were placed in a stressful situation, they produced more ABA to try to conserve any water they had in their leaves.<ref name=":02" /> Another extremely important factor in dealing with drought stress and regulating the uptake and export of water is [[aquaporin]]s (AQPs). AQPs are integral membrane proteins that make up channels. These channels' main job is the transport of water and other essential [[solute]]s. AQPs are both transcriptionally and post-transcriptionally regulated by many different factors such as ABA, GA3, pH and Ca<sup>2+</sup>; and the specific levels of AQPs in certain parts of the plant, such as roots or leaves, helps to draw as much water into the plant as possible.<ref>{{Cite journal|last1=Zargar|first1=Sajad Majeed|last2=Nagar|first2=Preeti|last3=Deshmukh|first3=Rupesh|last4=Nazir|first4=Muslima|last5=Wani|first5=Aijaz Ahmad|last6=Masoodi|first6=Khalid Zaffar|last7=Agrawal|first7=Ganesh Kumar|last8=Rakwal|first8=Randeep|date=October 2017|title=Aquaporins as potential drought tolerance inducing proteins: Towards instigating stress tolerance|journal=Journal of Proteomics|volume=169|pages=233–238|doi=10.1016/j.jprot.2017.04.010|pmid=28412527|issn=1874-3919}}</ref> By understanding the mechanisms of both AQPs and the hormone ABA, scientists will be better able to produce drought-resistant plants in the future.

A study by Tombesi et al., found that plants which had previously been exposed to drought were able to minimize water loss and decrease water use.<ref name=":1">{{Cite journal|last1=Tombesi|first1=Sergio|last2=Frioni|first2=Tommaso|last3=Poni|first3=Stefano|last4=Palliotti|first4=Alberto|date=June 2018|title=Effect of water stress "memory" on plant behavior during subsequent drought stress|journal=Environmental and Experimental Botany|volume=150|pages=106–114|doi=10.1016/j.envexpbot.2018.03.009|bibcode=2018EnvEB.150..106T |s2cid=90058393|issn=0098-8472}}</ref> They found that plants which were exposed to drought conditions actually changed the way they regulated their stomata and what they called "hydraulic safety margin" so as to decrease the vulnerability of the plant. By changing the regulation of stomata and subsequently the transpiration, plants were able to function better when less water was available.<ref name=":1" />