Editing Plant hormone (section)

===Salicylic acid===
[[File:2-hydroxybenzoic acid 200.svg|thumb|Salicylic acid|155px]]
[[Salicylic acid#Plant hormone|Salicylic acid]] (SA) is a hormone with a structure related to [[benzoic acid]] and [[phenol]]. It was originally isolated from an extract of [[Salix alba|white willow]] bark (''Salix alba'') and is of great interest to human medicine, as it is the precursor of the painkiller [[aspirin]]. In plants, SA plays a critical role in the defense against biotrophic pathogens. In a similar manner to JA, SA can also become [[Methylation|methylated]]. Like MeJA, [[methyl salicylate]] is volatile and can act as a long-distance signal to neighboring plants to warn of pathogen attack. In addition to its role in defense, SA is also involved in the response of plants to abiotic stress, particularly from drought, extreme temperatures, heavy metals, and osmotic stress.<ref>{{cite journal | vauthors = Rivas-San Vicente M, Plasencia J | title = Salicylic acid beyond defence: its role in plant growth and development | journal = Journal of Experimental Botany | volume = 62 | issue = 10 | pages = 3321–38 | date = June 2011 | pmid = 21357767 | doi = 10.1093/jxb/err031 | doi-access = free }}</ref>

Salicylic acid (SA) serves as a key hormone in plant innate immunity, including resistance in both local and systemic tissue upon biotic attacks, hypersensitive responses, and cell death. Some of the SA influences on plants include seed germination, cell growth, respiration, stomatal closure, senescence-associated gene expression, responses to abiotic and biotic stresses, basal thermo tolerance and fruit yield. A possible role of salicylic acid in signaling disease resistance was first demonstrated by injecting leaves of resistant tobacco with SA.<ref>{{cite journal | vauthors = Dempsey DA, Klessig DF | title = How does the multifaceted plant hormone salicylic acid combat disease in plants and are similar mechanisms utilized in humans? | journal = BMC Biology | volume = 15 | issue = 1 | pages = 23 | date = March 2017 | pmid = 28335774 | pmc = 5364617 | doi = 10.1186/s12915-017-0364-8 | doi-access = free }}</ref> The result was that injecting SA stimulated pathogenesis related (PR) protein accumulation and enhanced resistance to tobacco mosaic virus (TMV) infection. Exposure to pathogens causes a cascade of reactions in the plant cells. SA biosynthesis is increased via isochorismate synthase (ICS) and phenylalanine ammonia-lyase (PAL) pathway in plastids.<ref>{{cite journal | vauthors = Kumar D | title = Salicylic acid signaling in disease resistance | journal = Plant Science | volume = 228 | pages = 127–34 | date = November 2014 | pmid = 25438793 | doi = 10.1016/j.plantsci.2014.04.014 }}</ref> It was observed that during plant-microbe interactions, as part of the defense mechanisms, SA is initially accumulated at the local infected tissue and then spread all over the plant to induce systemic acquired resistance at non-infected distal parts of the plant. Therefore with increased internal concentration of  SA, plants were able to build resistant barriers for pathogens and other adverse environmental conditions<ref>{{cite journal | vauthors = Ding P, Ding Y | title = Stories of Salicylic Acid: A Plant Defense Hormone | journal = Trends in Plant Science | volume = 25 | issue = 6 | pages = 549–565 | date = June 2020 | pmid = 32407695 | doi = 10.1016/j.tplants.2020.01.004 | s2cid = 213666131 }}</ref>