View source for Plant communication

{{short description|Communication between plants and other organisms}}
{{Primary sources|date=October 2021}} 
Plants are exposed to many stress factors such as disease, temperature changes, herbivory, injury and more. Therefore, in order to respond or be ready for any kind of physiological state, they need to develop some sort of system for their survival in the moment and/or for the future. '''Plant communication''' encompasses communication using volatile organic compounds, electrical signaling, and common mycorrhizal networks between plants and a host of other organisms such as [[soil microbe]]s,<ref>{{Cite journal |last1=Wenke |first1=Katrin |last2=Kai |first2=Marco |last3=Piechulla |first3=Birgit|s2cid=1409780 |date=2010-02-01 |title=Belowground volatiles facilitate interactions between plant roots and soil organisms|journal=Planta |volume=231 |issue=3 |pages=499–506|doi=10.1007/s00425-009-1076-2|pmid=20012987 |bibcode=2010Plant.231..499W }}</ref> other plants<ref>{{cite journal |last1=Yoneya|first1=Kinuyo|last2=Takabayashi |first2=Junji |date=2014-01-01 |title=Plant–plant communication mediated by airborne signals: ecological and plant physiological perspectives|journal=Plant Biotechnology |volume=31 |issue=5 |pages=409–416 |doi=10.5511/plantbiotechnology.14.0827a|doi-access=free }}</ref> (of the same or other species), animals,<ref>{{Cite journal|last1=Leonard |first1=Anne S. |last2=Francis|first2=Jacob S. |s2cid=9578593 |date=2017-04-01 |title=Plant–animal communication: past, present and future|journal=Evolutionary Ecology| volume=31 |issue=2 |pages=143–151 |doi=10.1007/s10682-017-9884-5|bibcode=2017EvEco..31..143L }}</ref> insects,<ref name=":1">{{Cite journal |last1=De Moraes |first1=C. M.|last2=Lewis |first2=W. J.|last3=Paré |first3=P. W.|last4=Alborn|first4=H. T.|last5=Tumlinson|first5=J. H.|s2cid=4346152|title=Herbivore-infested plants selectively attract parasitoids|journal=Nature|volume=393|issue=6685|pages=570–573|doi=10.1038/31219|year=1998|bibcode=1998Natur.393..570D}}</ref> and fungi.<ref>{{Cite journal |last1=Bonfante |first1=Paola |last2=Genre |first2=Andrea|title=Arbuscular mycorrhizal dialogues: do you speak 'plantish' or 'fungish'? |journal=Trends in Plant Science |volume=20 |issue=3|pages=150–154 |doi=10.1016/j.tplants.2014.12.002|pmid=25583176 |year=2015 |hdl=2318/158569 |hdl-access=free }}</ref> Plants communicate through a host of [[volatile organic compound]]s (VOCs) that can be separated into four broad categories, each the product of distinct chemical pathways: [[fatty acid]] derivatives, [[phenylpropanoid]]s/[[benzenoids]], [[amino acid]] derivatives, and [[terpenoid]]s.<ref name=":2">{{Cite journal|last=Dudareva|first=Natalia|s2cid=26160875|date=April 2013 |title=Biosynthesis, function and metabolic engineering of plant volatile organic compounds |jstor=newphytologist.198.1.16 |journal=New Phytologist |volume=198 |issue=1|pages=16–32|doi=10.1111/nph.12145|pmid=23383981}}</ref> Due to the physical/chemical constraints most VOCs are of low molecular mass (< 300 Da), are [[hydrophobic]], and have high vapor pressures.<ref>{{Cite journal |last1=Rohrbeck |first1=D. |last2=Buss |first2=D.|last3=Effmert |first3=U. |last4=Piechulla |first4=B. |s2cid=40502773 |date=2006-09-01 |title=Localization of Methyl Benzoate Synthesis and Emission in Stephanotis floribunda and Nicotiana suaveolens Flowers |journal=Plant Biology |volume=8 |issue=5 |pages=615–626 |doi=10.1055/s-2006-924076|pmid=16755462 |bibcode=2006PlBio...8..615R }}</ref> The responses of organisms to plant emitted VOCs varies from attracting the predator of a specific [[herbivore]] to reduce mechanical damage inflicted on the plant <ref name=":1" /> to the induction of chemical defenses of a neighboring plant before it is being attacked.<ref name=":0">{{cite journal |jstor=1691120|title=Rapid Changes in Tree Leaf Chemistry Induced by Damage: Evidence for Communication between Plants|last1=Baldwin|first1=Jan T.|last2=Schultz|first2=Jack C.|s2cid=31818182|journal=Science|year=1983|volume=221|issue=4607|pages=277–279|doi=10.1126/science.221.4607.277|pmid=17815197|bibcode=1983Sci...221..277B}}</ref> In addition, the host of VOCs emitted varies from plant to plant, where for example, the [[Venus flytrap|Venus Fly Trap]] can emit VOCs to specifically target and attract starved prey.<ref>{{Cite journal|last1=Hedrich|first1=Rainer|last2=Neher|first2=Erwin|date=March 2018|title=Venus Flytrap: How an Excitable, Carnivorous Plant Works|url=https://www.cell.com/trends/plant-science/pdf/S1360-1385(17)30280-7.pdf?code=cell-site|journal=Trends in Plant Science|language=en|volume=23|issue=3|pages=220–234|doi=10.1016/j.tplants.2017.12.004|pmid=29336976|issn=1360-1385}}</ref> While these VOCs typically lead to increased resistance to herbivory in neighboring plants, there is no clear benefit to the emitting plant in helping nearby plants. As such, whether neighboring plants have evolved the capability to "eavesdrop" or whether there is an unknown tradeoff occurring is subject to much scientific debate.<ref>{{Cite journal|date=2010-03-01|title=Explaining evolution of plant communication by airborne signals|journal=Trends in Ecology & Evolution|volume=25|issue=3|pages=137–144|doi=10.1016/j.tree.2009.09.010|pmid=19837476|issn=0169-5347|last1=Heil|first1=Martin|last2=Karban|first2=Richard}}</ref>
As related to the aspect of meaning-making, the field is also identified as [[phytosemiotics]].<ref>[[Kalevi Kull|Kull, Kalevi]] 2000. [https://www.academia.edu/3520416/An_introduction_to_phytosemiotics_Semiotic_botany_and_vegetative_sign_systems An introduction to phytosemiotics: Semiotic botany and vegetative sign systems]. ''[[Sign Systems Studies]]'' 28: 326–350.</ref>

== Volatile communication ==
In Runyon et al. 2006, the researchers demonstrate how the [[parasitic plant]], ''[[Cuscuta pentagona]]'' (field dodder), uses VOCs to interact with various hosts and determine locations. Dodder seedlings show direct growth toward [[tomato]] plants (''Lycopersicon esculentum'') and, specifically, tomato plant volatile organic compounds. This was tested by growing a dodder weed seedling in a contained environment, connected to two different chambers. One chamber contained tomato VOCs while the other had artificial tomato plants. After 4 days of growth, the dodder weed seedling showed a significant growth towards the direction of the chamber with tomato VOC's. Their experiments also showed that the dodder weed seedlings could distinguish between wheat (''Triticum aestivum'') VOCs and tomato plant volatiles. As when one chamber was filled with each of the two different VOCs, dodder weeds grew towards tomato plants as one of the wheat VOC's is repellent. These findings show evidence that volatile organic compounds determine ecological interactions between plant species and show statistical significance that the dodder weed can distinguish between different plant species by sensing their VOCs.<ref>{{Cite journal| doi = 10.1126/science.1131371| issn = 1095-9203| volume = 313| issue = 5795| pages = 1964–1967| last1 = Runyon| first1 = Justin B.| last2 = Mescher| first2 = Mark C.| last3 = De Moraes| first3 = Consuelo M.| title = Volatile chemical cues guide host location and host selection by parasitic plants| journal = Science| date = 2006-09-29| pmid = 17008532| bibcode = 2006Sci...313.1964R| s2cid = 10477465}}</ref>

Tomato plant to plant communication is further examined in Zebelo et al. 2012, which studies tomato plant response to herbivory. Upon herbivory by ''[[Spodoptera littoralis]]'', tomato plants emit VOCs that are released into the atmosphere and induce responses in neighboring tomato plants. When the herbivory-induced VOCs bind to receptors on other nearby tomato plants, responses occur within seconds. The neighboring plants experience a rapid depolarization in cell potential and increase in cytosolic calcium. Plant receptors are most commonly found on plasma membranes as well as within the cytosol, endoplasmic reticulum, nucleus, and other cellular compartments. VOCs that bind to plant receptors often induce signal amplification by action of secondary messengers including calcium influx as seen in response to neighboring herbivory. These emitted volatiles were measured by GC-MS and the most notable were 2-hexenal and 3-hexenal acetate. It was found that depolarization increased with increasing [[green leaf volatile]] concentrations. These results indicate that tomato plants communicate with one another via airborne volatile cues, and when these VOC's are perceived by receptor plants, responses such as depolarization and calcium influx occur within seconds.<ref>{{Cite journal| doi = 10.1016/j.plantsci.2012.08.006| issn = 0168-9452| volume = 196| pages = 93–100| last1 = Zebelo| first1 = Simon A.| last2 = Matsui| first2 = Kenji| last3 = Ozawa| first3 = Rika| last4 = Maffei| first4 = Massimo E.| title = Plasma membrane potential depolarization and cytosolic calcium flux are early events involved in tomato (Solanum lycopersicon) plant-to-plant communication| journal = Plant Science| access-date = 2020-10-20| date = 2012-11-01| pmid = 23017903| url = http://www.sciencedirect.com/science/article/pii/S0168945212001641}}</ref>

=== Terpenoids ===
[[File:Verbenone3D.png|thumb|The [[terpenoid]] [[verbenone]] is a plant [[pheromone]], signalling to insects that a tree is already infested by beetles.<ref>{{cite book | last1=Mafra-Neto | first1=Agenor| last2=de Lame | first2=Frédérique M.  | last3=Fettig | first3=Christopher J. | last4=Perring | first4=Thomas M. | last5=Stelinski | first5=Lukasz L.  | last6=Stoltman | first6=Lyndsie L.| last7=Mafra | first7=Leandro E. J. | last8=Borges | first8=Rafael | last9=Vargas | first9=Roger I. | chapter=Manipulation of Insect Behavior with Specialized Pheromone and Lure Application Technology (SPLAT®) | title= Natural Products for Pest Management | editor=John Beck |editor2=Joel Coats |editor3=Stephen Duke |editor4=Marja Koivunen | publisher=American Chemical Society | volume=1141 | pages=31–58 | year=2013}}</ref>]]
{{further|Terpenoid}}

Terpenoids facilitate communication between plants and insects, mammals, fungi, microorganisms, and other plants.<ref>{{cite journal |last1=Llusià |first1=Joan |last2=Estiarte |first2=Marc |last3=Peñuelas |first3=Josep |date=1996 |title=Terpenoids and plant communication |journal=Bull. Inst. Cat. Hist. Nat. |volume=64 |pages=125–133}}</ref> Terpenoids may act as both attractants and repellants for various insects. For example, pine shoot beetles (''[[Tomicus piniperda]]'') are attracted to certain monoterpenes ( (+/-)-[[A-Pinene|a-pinene]], (+)-[[Carene|3-carene]] and terpinolene) produced by Scots pines ''([[Scots pine|Pinus sylvestris]]''), while being repelled by others (such as [[verbenone]]).<ref>{{cite journal |last1=Byers |first1=J. A. |last2=Lanne |first2=B. S. |last3=Löfqvist |first3=J. |s2cid=10669662 |date=1989-05-01 |title=Host tree unsuitability recognized by pine shoot beetles in flight |journal=Experientia |volume=45 |issue=5 |pages=489–492 |doi=10.1007/BF01952042|issn=0014-4754}}</ref>

Terpenoids are a large family of biological molecules with over 22,000 compounds.<ref>{{Cite book |title=Dictionary of terpenoids |last1=Hill |first1=Ruaraidh |last2=Connolly |first2=J.D. |date=1991 |publisher=Chapman & Hall |isbn=978-0412257704 |oclc=497430488}}</ref> Terpenoids are similar to [[terpene]]s in their carbon skeleton but unlike terpenes contain [[functional group]]s. The structure  of terpenoids is described by the [[biogenetic isoprene rule]] which states that terpenoids can be thought of being made of [[isoprenoid]] subunits, arranged either regularly or irregularly.<ref>{{cite journal |title=The isoprene rule and the biogenesis of terpenic compounds |first=Leopold |last=Ružička |s2cid=44195550 |journal=[[Cellular and Molecular Life Sciences]] |volume=9 |issue=10 |pages=357–367 |year=1953 |doi=10.1007/BF02167631 |pmid=13116962 }}</ref> The biosynthesis of terpenoids occurs via the [[Non-mevalonate pathway|methylerythritol phosphate]] (MEP) and  [[Mevalonate pathway|mevalonic acid]](MVA) pathways<ref name=":2" /> both of which include [[Isopentenyl pyrophosphate|isopentenyl diphosphate]] (IPP) and [[Dimethylallyl pyrophosphate|dimethylallyl diphosphate]] (DMAPP) as key components.<ref>{{Cite journal |last1=McGarvey |first1=Douglas J. |last2=Croteau |first2=Rodney |date=July 1995 |title=Terpenoid Metabolism |jstor=3870054 |journal=The Plant Cell |volume=7 |issue=7 |pages=1015–1026|doi=10.1105/tpc.7.7.1015 |pmid=7640522 |pmc=160903 }}</ref> The MEP pathway produces [[hemiterpene]]s, [[monoterpene]]s, [[diterpene]]s, and volatile [[carotenoid]] derivatives while the MVA pathway produces [[sesquiterpene]]s.<ref name=":2" />

== Electrical signaling ==
Many researchers have shown that plants have the ability to use electrical signaling to communicate from leaves to stem to roots. Starting in the late 1800s scientists, such as [[Charles Darwin]], examined ferns and Venus fly traps because they showed excitation patterns similar to animal nerves.<ref>{{Cite book|last=Darwin|first=Charles|title=Insectivorous Plants|year=1875|location=London}}</ref> However, the mechanisms behind this electrical signaling are not well known and are a current topic of ongoing research.<ref name=":6">{{Cite journal|date=2016-05-01|title=Electrical Wiring and Long-Distance Plant Communication|url=https://www.sciencedirect.com/science/article/abs/pii/S1360138516000327|journal=Trends in Plant Science|language=en|volume=21|issue=5|pages=376–387|doi=10.1016/j.tplants.2016.01.016|issn=1360-1385|last1=Hedrich|first1=Rainer|last2=Salvador-Recatalà|first2=Vicenta|last3=Dreyer|first3=Ingo|pmid=26880317}}</ref> A plant may produce electrical signaling in response to wounding, temperature extremes, high salt conditions, drought conditions, and other various stimuli.<ref name=":6" /><ref>{{Cite journal|last1=Furch|first1=Alexandra C. U.|last2=Zimmermann|first2=Matthias R.|last3=Will|first3=Torsten|last4=Hafke|first4=Jens B.|last5=van Bel|first5=Aart J. E.|date=2010-08-01|title=Remote-controlled stop of phloem mass flow by biphasic occlusion in Cucurbita maxima|url=https://doi.org/10.1093/jxb/erq181|journal=Journal of Experimental Botany|volume=61|issue=13|pages=3697–3708|doi=10.1093/jxb/erq181|pmid=20584788|issn=0022-0957|pmc=2921205}}</ref>

There are two types of electrical signals that a plant uses. The first is the [[action potential]] and the second is the [[variation potential]].

Similar to action potentials in animals, [[action potential]]s in plants are characterized as “all or nothing.”<ref name=":7">{{Cite journal|last1=Sukhov|first1=Vladimir|last2=Vodeneev|first2=Vladimir|date=2009-11-17|title=A Mathematical Model of Action Potential in Cells of Vascular Plants|url=https://doi.org/10.1007/s00232-009-9218-9|journal=Journal of Membrane Biology|language=en|volume=232|issue=1|pages=59–67|doi=10.1007/s00232-009-9218-9|pmid=19921324|s2cid=13334600|issn=1432-1424}}</ref> This is the understood mechanism for how plant [[action potential]]s are initiated:<ref name=":8">{{Cite journal|date=2011-12-21|title=Simulation of action potential propagation in plants|url=https://www.sciencedirect.com/science/article/abs/pii/S0022519311004759|journal=Journal of Theoretical Biology|language=en|volume=291|pages=47–55|doi=10.1016/j.jtbi.2011.09.019|issn=0022-5193|last1=Sukhov|first1=Vladimir|last2=Nerush|first2=Vladimir|last3=Orlova|first3=Lyubov|last4=Vodeneev|first4=Vladimir|pmid=21959317|bibcode=2011JThBi.291...47S}}</ref><ref name=":9">{{Cite journal|last1=Fromm|first1=Jörg|last2=Lautner|first2=Silke|date=2007|title=Electrical signals and their physiological significance in plants|journal=Plant, Cell & Environment|language=en|volume=30|issue=3|pages=249–257|doi=10.1111/j.1365-3040.2006.01614.x|pmid=17263772|issn=1365-3040|doi-access=free}}</ref><ref name=":7" /><ref name=":10">{{Cite journal|last1=Vodeneev|first1=V. A.|last2=Opritov|first2=V. A.|last3=Pyatygin|first3=S. S.|date=2006-07-01|title=Reversible changes of extracellular pH during action potential generation in a higher plant Cucurbita pepo|url=https://doi.org/10.1134/S102144370604008X|journal=Russian Journal of Plant Physiology|language=en|volume=53|issue=4|pages=481–487|doi=10.1134/S102144370604008X|s2cid=5037025|issn=1608-3407}}</ref><ref name=":11">{{Cite journal|last1=Krol|first1=Elzbieta|last2=Dziubinska|first2=Halina|last3=Trebacz|first3=Kazimierz|date=2003-05-15|title=Low-Temperature Induced Transmembrane Potential Changes in the Liverwort Conocephalum conicum|journal=Plant and Cell Physiology|volume=44|issue=5|pages=527–533|doi=10.1093/pcp/pcg070|pmid=12773639|issn=0032-0781|doi-access=}}</ref><ref name=":13">{{Cite journal|last1=Wacke|first1=M.|last2=Thiel|first2=G.|last3=Hütt|first3=M.-T.|date=2003-02-01|title=Ca2+ Dynamics during Membrane Excitation of Green Alga Chara: Model Simulations and Experimental Data|url=https://doi.org/10.1007/s00232-002-1054-0|journal=The Journal of Membrane Biology|language=en|volume=191|issue=3|pages=179–192|doi=10.1007/s00232-002-1054-0|pmid=12571752|s2cid=15569873|issn=1432-1424}}</ref><ref name=":14">{{Cite journal|last1=Tucker|first1=E. B.|last2=Boss|first2=W. F.|date=June 1996|title=Mastoparan-Induced Intracellular Ca2+ Fluxes May Regulate Cell-to-Cell Communication in Plants.|journal=Plant Physiology|volume=111|issue=2|pages=459–467|doi=10.1104/pp.111.2.459|issn=0032-0889|pmid=12226302|pmc=157856}}</ref>

* A stimulus transitorily and reversibly activates calcium ion channels
* A short burst of calcium ions into the cell through the open calcium channels
* Calcium ions reversibly inactivate [[Proton ATPase|H+-ATPase]] activity
* [[Depolarization]] (due to calcium ion influx) activates voltage gated chloride channels causing chloride ions to leave the cell and cause further depolarization
* [[Calcium ATPase|Calcium-ATPases]] decreases intracellular calcium concentration by pumping calcium ions to the outside of the cell (this allows for the H+-ATPase to be reactivated and repolarization to be initiated)
* [[Repolarization]] occurs when the activated [[H+-ATPase]] pumps H+ out of the cell and the open K+ channels allow for the flow of K+ to the outside of the cell

Plant [[resting membrane potential]]s range from -80 to -200 mV.<ref name=":9" /><ref name=":8" /> High H+-ATPase activity corresponds with [[Hyperpolarization (biology)|hyperpolarization]] (up to -200mV), making it harder to depolarize and fire an action potential.<ref name=":8" /><ref name=":7" /><ref name=":10" /><ref name=":15">{{Cite journal|last1=Johns|first1=Sarah|last2=Hagihara|first2=Takuma|last3=Toyota|first3=Masatsugu|last4=Gilroy|first4=Simon|date=2021-04-02|title=The fast and the furious: rapid long-range signaling in plants|journal=Plant Physiology|volume=185|issue=3|pages=694–706|doi=10.1093/plphys/kiaa098|issn=1532-2548|pmc=8133610|pmid=33793939}}</ref> This is why it is essential for calcium ions to inactivate H+-ATPase activity so that depolarization can be reached.<ref name=":7" /><ref name=":10" /> When the voltage gated chloride channels are activated and full depolarization occurs, calcium ions are pumped out of the cell (via a calcium-ATPase) after so that H+-ATPase activity resumes so that the cell can repolarize.<ref name=":7" /><ref name=":10" />

Calcium's interaction with the H+-ATPase is through a [[kinase]].<ref name=":10" /> Therefore, calcium's influx causes the activation of a kinase that [[Phosphorylation|phosphorylates]] and deactivates the H+-ATPase so that the cell can depolarize.<ref name=":10" /> It is unclear whether all of the heightened calcium ion intracellular concentration is solely due to calcium channel activation. It is possible that the transitory activation of calcium channels causes an influx of calcium ions into the cell which activates intracellular stores of calcium ions to be released and subsequently causes depolarization (through the inactivation of H+-ATPase and activation of voltage gated chloride channels).<ref name=":10" /><ref name=":11" /><ref name=":13" /><ref name=":14" />

[[Variation potential]]s have proven hard to study and their mechanism is less well known than action potentials.<ref name=":16">{{Cite journal|date=2001-01-01|title=Transmission route for action potentials and variation potentials in Helianthus annuus L.|url=https://www.sciencedirect.com/science/article/abs/pii/S0176161704701431|journal=Journal of Plant Physiology|language=en|volume=158|issue=9|pages=1167–1172|doi=10.1078/S0176-1617(04)70143-1|issn=0176-1617|last1=Dziubińska|first1=Halina|last2=Trębacz|first2=Kazimierz|last3=Zawadzki|first3=Tadeusz}}</ref> Variation potentials are slower than action potentials, are not considered “all or nothing,” and they themselves can trigger several action potentials.<ref name=":9" /><ref name=":16" /><ref name=":15" /><ref name=":17">{{Cite journal|last=Pickard|first=Barbara G.|date=1973|title=Action Potentials in Higher Plants|url=https://www.jstor.org/stable/4353850|journal=Botanical Review|volume=39|issue=2|pages=172–201|doi=10.1007/BF02859299|jstor=4353850|bibcode=1973BotRv..39..172P |s2cid=5026557|issn=0006-8101}}</ref> The current understanding is that upon wounding or other stressful events, a plant's [[turgor pressure]] changes which releases a [[Hydraulic signaling in plants|hydraulic wave]] throughout the plant that is transmitted through the [[xylem]].<ref name=":9" /><ref>{{Cite journal|last1=Stankovic|first1=B.|last2=Zawadzki|first2=T.|last3=Davies|first3=E.|date=November 1997|title=Characterization of the Variation Potential in Sunflower.|journal=Plant Physiology|volume=115|issue=3|pages=1083–1088|doi=10.1104/pp.115.3.1083|issn=0032-0889|pmid=12223859|pmc=158572}}</ref> This hydraulic wave may activate pressure gated channels due to the sudden change in pressure.<ref>{{Cite journal|last1=Farmer|first1=Edward E.|last2=Gao|first2=Yong-Qiang|last3=Lenzoni|first3=Gioia|last4=Wolfender|first4=Jean-Luc|last5=Wu|first5=Qian|date=2020|title=Wound- and mechanostimulated electrical signals control hormone responses|journal=New Phytologist|language=en|volume=227|issue=4|pages=1037–1050|doi=10.1111/nph.16646|pmid=32392391|issn=1469-8137|doi-access=free}}</ref> Their ionic mechanism is very different from action potentials and is thought to involve the inactivation of the [[P-type ATPase|P-type H+-ATPase]].<ref name=":9" /><ref>{{Citation|last1=Stahlberg|first1=Rainer|title=Slow Wave Potentials — a Propagating Electrical Signal Unique to Higher Plants|date=2006|url=https://doi.org/10.1007/978-3-540-28516-8_20|work=Communication in Plants: Neuronal Aspects of Plant Life|pages=291–308|editor-last=Baluška|editor-first=František|place=Berlin, Heidelberg|publisher=Springer|language=en|doi=10.1007/978-3-540-28516-8_20|isbn=978-3-540-28516-8|access-date=2021-06-03|last2=Cleland|first2=Robert E.|last3=Van Volkenburgh|first3=Elizabeth|editor2-last=Mancuso|editor2-first=Stefano|editor3-last=Volkmann|editor3-first=Dieter}}</ref>

Long distance electrical signaling in plants is characterized by electrical signaling that occurs over distances greater than the span of a single cell.<ref name=":18">{{Cite journal|last1=Thain|first1=J.F.|last2=Wildon|first2=D.C.|date=1992|title=Electrical signalling in plants|url=https://www.jstor.org/stable/43421317|journal=Science Progress (1933- )|volume=76|issue=3/4 (301/302)|pages=553–564|jstor=43421317|issn=0036-8504}}</ref> In 1873, [[John Burdon-Sanderson|Sir John Burdon-Sanderson]] described action potentials and their long-distance propagation throughout plants.<ref name=":17" /> Action potentials in plants are carried out through a plants vascular network (particularly the [[phloem]]),<ref name=":19">{{Cite journal|last1=Volkov|first1=Alexander G.|last2=Shtessel|first2=Yuri B.|date=2020-01-01|title=Underground electrotonic signal transmission between plants|url=https://doi.org/10.1080/19420889.2020.1757207|journal=Communicative & Integrative Biology|volume=13|issue=1|pages=54–58|doi=10.1080/19420889.2020.1757207|pmc=7202782|pmid=32395195}}</ref> a network of tissues that connects all of the various plant organs, transporting signaling molecules throughout the plant.<ref name=":18" /> Increasing the frequency of [[action potential]]s causes the [[phloem]] to become increasingly [[Cross-link|cross linked]].<ref>{{Cite journal|last1=Calvo|first1=Paco|last2=Sahi|first2=Vaidurya Pratap|last3=Trewavas|first3=Anthony|date=2017|title=Are plants sentient?|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/pce.13065|journal=Plant, Cell & Environment|language=en|volume=40|issue=11|pages=2858–2869|doi=10.1111/pce.13065|pmid=28875517|issn=1365-3040}}</ref> In the phloem, the propagation of action potentials is dictated by the fluxes of chloride, potassium, and calcium ions, but the exact mechanism for propagation is not well understood.<ref>{{Cite journal|last1=Fromm|first1=Joerg|last2=Hajirezaei|first2=Mohammad-Reza|last3=Becker|first3=Verena Katharina|last4=Lautner|first4=Silke|date=2013|title=Electrical signaling along the phloem and its physiological responses in the maize leaf|journal=Frontiers in Plant Science|language=English|volume=4|page=239|doi=10.3389/fpls.2013.00239|pmid=23847642|issn=1664-462X|pmc=3701874|doi-access=free}}</ref> Alternatively, the transport of action potentials over short, local distances is distributed throughout the plant via [[plasmodesma]]tal connections between cells.<ref name=":19" />

When a plant responds to stimuli, sometimes the response time is nearly instantaneous which is much faster than chemical signals are able to travel. Current research suggests that electrical signaling may be responsible.<ref>{{Cite journal|last1=Wildon|first1=D. C.|last2=Thain|first2=J. F.|last3=Minchin|first3=P. E. H.|last4=Gubb|first4=I. R.|last5=Reilly|first5=A. J.|last6=Skipper|first6=Y. D.|last7=Doherty|first7=H. M.|last8=O'Donnell|first8=P. J.|last9=Bowles|first9=D. J.|date=November 1992|title=Electrical signalling and systemic proteinase inhibitor induction in the wounded plant|url=https://www.nature.com/articles/360062a0|journal=Nature|language=en|volume=360|issue=6399|pages=62–65|doi=10.1038/360062a0|bibcode=1992Natur.360...62W|s2cid=4274162|issn=1476-4687}}</ref><ref name=":20">{{Cite journal|last1=Vian|first1=Alain|last2=Henry-Vian|first2=Chantal|last3=Davies|first3=Eric|date=October 1999|title=Rapid and Systemic Accumulation of Chloroplast mRNA-Binding Protein Transcripts after Flame Stimulus in Tomato|journal=Plant Physiology|volume=121|issue=2|pages=517–524|doi=10.1104/pp.121.2.517|issn=0032-0889|pmid=10517843|pmc=59414}}</ref><ref name=":21">{{Cite journal|last1=Stanković|first1=Bratislav|last2=Davies|first2=Eric|date=1997-07-01|title=Intercellular communication in plants: electrical stimulation of proteinase inhibitor gene expression in tomato|url=https://doi.org/10.1007/s004250050143|journal=Planta|language=en|volume=202|issue=4|pages=402–406|doi=10.1007/s004250050143|bibcode=1997Plant.202..402S |s2cid=5018084|issn=1432-2048}}</ref><ref name=":23">{{Cite journal|last1=Roux|first1=David|last2=Vian|first2=Alain|last3=Girard|first3=Sébastien|last4=Bonnet|first4=Pierre|last5=Paladian|first5=Françoise|last6=Davies|first6=Eric|last7=Ledoigt|first7=Gérard|date=2006|title=Electromagnetic fields (900 MHz) evoke consistent molecular responses in tomato plants|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1399-3054.2006.00740.x|journal=Physiologia Plantarum|language=en|volume=128|issue=2|pages=283–288|doi=10.1111/j.1399-3054.2006.00740.x|issn=1399-3054}}</ref> In particular, the response of a plant to a wound is triphasic.<ref name=":20" /> Phase 1 is an immediate great increase in expression of target genes.<ref name=":20" /> Phase 2 is a period of dormancy.<ref name=":20" /> Phase 3 is a weakened and delayed upregulation of the same target genes as phase 1.<ref name=":20" /> In phase 1, the speed of upregulation is nearly instantaneous which has led researchers to theorize that the initial response from a plant is through action potentials and variation potentials as opposed to chemical or hormonal signaling which is most likely responsible for the phase 3 response.<ref name=":20" /><ref name=":21" /><ref name=":23" />

Upon stressful events, there is variation in a plant's response. That is to say, it is not always the case that a plant responds with an [[action potential]] or [[variation potential]].<ref name=":20" /> However, when a plant does generate either an action potential or variation potential, one of the direct effects can be an [[upregulation]] of a certain gene's expression.<ref name=":21" /> In particular, [[Protease inhibitor (biology)|protease inhibitors]] and [[calmodulin]] exhibit rapid upregulated gene expression.<ref name=":21" /> Additionally, [[ethylene]] has shown quick upregulation in the fruit of a plant as well as [[jasmonate]] in neighboring leaves to a wound.<ref>{{Cite journal|last1=Inaba|first1=Akitsugu|last2=Manabe|first2=Taro|last3=Tsuji|first3=Hiroyuki|last4=Iwamoto|first4=Tomotada|date=1995|title=Electrical Impedance Analysis of Tissue Properties Associated with Ethylene Induction by Electric Currents in Cucumber (Cucumis sativus L.) Fruit|journal=Plant Physiology|volume=107|issue=1|pages=199–205|doi=10.1104/pp.107.1.199|jstor=4276290|pmid=12228354|pmc=161186|issn=0032-0889}}</ref><ref>{{Cite journal|last1=Salvador-Recatalà|first1=Vicenta|last2=Tjallingii|first2=W. Freddy|last3=Farmer|first3=Edward E.|date=2014|title=Real-time, in vivo intracellular recordings of caterpillar-induced depolarization waves in sieve elements using aphid electrodes|journal=New Phytologist|language=en|volume=203|issue=2|pages=674–684|doi=10.1111/nph.12807|pmid=24716546|s2cid=19489725 |issn=1469-8137|doi-access=free}}</ref> Aside from gene expression, action potentials and variation potentials also can result in [[stoma]]tal and leaf movement.<ref>{{Cite journal|last1=Devireddy|first1=Amith R.|last2=Arbogast|first2=Jimmie|last3=Mittler|first3=Ron|date=2020|title=Coordinated and rapid whole-plant systemic stomatal responses|journal=New Phytologist|language=en|volume=225|issue=1|pages=21–25|doi=10.1111/nph.16143|pmid=31454419|issn=1469-8137|doi-access=free}}</ref><ref>{{Cite journal|last1=Kurenda|first1=Andrzej|last2=Nguyen|first2=Chi Tam|last3=Chételat|first3=Aurore|last4=Stolz|first4=Stéphanie|last5=Farmer|first5=Edward E.|date=2019-12-17|title=Insect-damaged Arabidopsis moves like wounded Mimosa pudica|journal=Proceedings of the National Academy of Sciences|language=en|volume=116|issue=51|pages=26066–26071|doi=10.1073/pnas.1912386116|issn=0027-8424|pmid=31792188|pmc=6926025|bibcode=2019PNAS..11626066K |doi-access=free}}</ref>

In summary, electric signaling in plants is a powerful tool of communication and controls a plant's response to dangerous stimuli (like [[Herbivore|herbivory]]), helping to maintain [[homeostasis]].

== Below-ground communication ==
===Chemical Cues===
''[[Pisum sativum]]'' (garden pea) plants communicate stress cues via their roots to allow neighboring unstressed plants to anticipate an abiotic stressor. Pea plants are commonly grown in temperate regions throughout the world.<ref name=":02">{{Cite web|title=PEA Pisum sativum|url=https://plants.usda.gov/plantguide/pdf/pg_pisa6.pdf|website=United States Department of Agriculture Natural Resources Conservation Service.}}</ref> However, this adaptation allows plants to anticipate abiotic stresses such as drought. In 2011, Falik et al. tested the ability of unstressed pea plants to sense and respond to stress cues by inducing osmotic stress on a neighboring plant.<ref name=":12">{{Cite journal|last1=Falik|first1=Omer|last2=Mordoch|first2=Yonat|last3=Quansah|first3=Lydia|last4=Fait|first4=Aaron|last5=Novoplansky|first5=Ariel|date=2011-11-02|editor-last=Kroymann|editor-first=Juergen|title=Rumor Has It…: Relay Communication of Stress Cues in Plants|journal=PLOS ONE|language=en|volume=6|issue=11|pages=e23625|doi=10.1371/journal.pone.0023625|pmid=22073135|pmc=3206794|bibcode=2011PLoSO...623625F|issn=1932-6203|doi-access=free}}</ref> Falik et al. subjected the root of an externally-induced plant to mannitol in order to inflict osmotic stress and drought-like conditions. Five unstressed plants neighbored both sides of this stressed plant. On one side, the unstressed plants shared their root system with their neighbors to allow for root communication. On the other side, the unstressed plants did not share root systems with their neighbors.<ref name=":12" />

Falik et al. found that unstressed plants demonstrated the ability to sense and respond to stress cues emitted from the roots of the osmotically stressed plant. Furthermore, the unstressed plants were able to send additional stress cues to other neighboring unstressed plants in order to relay the signal. A cascade effect of stomatal closure was observed in neighboring unstressed plants that shared their rooting system but was not observed in the unstressed plants that did not share their rooting system.<ref name=":12" /> Therefore, neighboring plants demonstrate the ability to sense, integrate, and respond to stress cues transmitted through roots. Although Falik et al. did not identify the chemical responsible for perceiving stress cues, research conducted in 2016 by Delory et al. suggests several possibilities. They found that plant roots synthesize and release a wide array of organic compounds including solutes and volatiles (i.e. terpenes).<ref name=":22">{{Cite journal|last1=Delory|first1=Benjamin M.|last2=Delaplace|first2=Pierre|last3=Fauconnier|first3=Marie-Laure|last4=du Jardin|first4=Patrick|date=May 2016|title=Root-emitted volatile organic compounds: can they mediate belowground plant-plant interactions?|journal=Plant and Soil|language=en|volume=402|issue=1–2|pages=1–26|doi=10.1007/s11104-016-2823-3|issn=0032-079X|doi-access=free|bibcode=2016PlSoi.402....1D }}</ref> They cited additional research demonstrating that root-emitted molecules have the potential to induce physiological responses in neighboring plants either directly or indirectly by modifying the soil chemistry.<ref name=":22" /> Moreover, Kegge et al. demonstrated that plants perceive the presence of neighbors through changes in water/nutrient availability, root exudates, and soil microorganisms.<ref name=":3">{{Cite journal|last1=Kegge|first1=Wouter|last2=Pierik|first2=Ronald|date=March 2010|title=Biogenic volatile organic compounds and plant competition|journal=Trends in Plant Science|language=en|volume=15|issue=3|pages=126–132|doi=10.1016/j.tplants.2009.11.007|pmid=20036599}}</ref>

Although the underlying mechanism behind stress cues emitted by roots remains largely unknown, Falik et al. suggested that the plant hormone abscisic acid (ABA) may be responsible for integrating the observed phenotypic response (stomatal closure).<ref name=":12" /> Further research is needed to identify a well-defined mechanism and the potential adaptive implications for priming neighbors in preparation for forthcoming abiotic stresses; however, a literature review by Robbins et al. published in 2014 characterized the root endodermis as a signaling control center in response to abiotic environmental stresses including drought.<ref name=":4">{{Cite journal|last1=Robbins|first1=N. E.|last2=Trontin|first2=C.|last3=Duan|first3=L.|last4=Dinneny|first4=J. R.|date=2014-10-01|title=Beyond the Barrier: Communication in the Root through the Endodermis|journal=Plant Physiology|language=en|volume=166|issue=2|pages=551–559|doi=10.1104/pp.114.244871|pmid=25125504|pmc=4213087|issn=0032-0889|doi-access=free}}</ref> They found that the plant hormone ABA regulates the root endodermal response under certain environmental conditions. In 2016 Rowe et al. experimentally validated this claim by showing that ABA regulated root growth under osmotic stress conditions.<ref name=":5">{{Cite journal|last1=Rowe|first1=James H.|last2=Topping|first2=Jennifer F.|last3=Liu|first3=Junli|last4=Lindsey|first4=Keith|date=July 2016|title=Abscisic acid regulates root growth under osmotic stress conditions via an interacting hormonal network with cytokinin, ethylene and auxin|journal=New Phytologist|language=en|volume=211|issue=1|pages=225–239|doi=10.1111/nph.13882|pmid=26889752|pmc=4982081|issn=0028-646X|doi-access=free}}</ref> Additionally, changes in cytosolic calcium concentrations act as signals to close stomata in response to drought stress cues. Therefore, the flux of solutes, volatiles, hormones, and ions are likely involved in the integration of the response to stress cues emitted by roots.

===Mycorrhizal networks===
{{Main|Plant to plant communication via mycorrhizal networks}}
Another form of plant communication occurs through their root networks. Through roots, plants can share many different resources including carbon, nitrogen, and other nutrients. This transfer of below ground carbon is examined in Philip et al. 2011. The goals of this paper were to test if carbon transfer was bi-directional, if one species had a net gain in carbon, and if more carbon was transferred through the soil pathway or common mycorrhizal network (CMN). CMNs occur when fungal mycelia link roots of plants together.<ref name=philip2010>Philip, L., S. Simard, and M. Jones. 2010. Pathways for below-ground carbon transfer between paper birch and Douglas-fir seedlings. Plant Ecology & Diversity 3:221–233.</ref> The researchers followed seedlings of paper birch and Douglas-fir in a greenhouse for 8 months, where hyphal linkages that crossed their roots were either severed or left intact. The experiment measured amounts of labeled carbon exchanged between seedlings. It was discovered that there was indeed a bi-directional sharing of carbon between the two tree species, with the Douglas-fir receiving a slight net gain in carbon. Also, the carbon was transferred through both soil and the CMN pathways, as transfer occurred when the CMN linkages were interrupted, but much more transfer occurred when the CMN's were left unbroken.

This experiment showed that through fungal mycelia linkage of the roots of two plants, plants are able to communicate with one another and transfer nutrients as well as other resources through below ground root networks.<ref name=philip2010/> Further studies go on to argue that this underground “tree talk” is crucial in the adaptation of forest ecosystems. Plant genotypes have shown that mycorrhizal fungal traits are heritable and play a role in plant behavior. These relationships with fungal networks can be mutualistic, commensal, or even parasitic. It has been shown that plants can rapidly change behavior such as root growth, shoot growth, photosynthetic rate, and defense mechanisms in response to mycorrhizal colonization.<ref>Gorzelak, M. A., A. K. Asay, B. J. Pickles, and S. W. Simard. 2015. Inter-plant communication through mycorrhizal networks mediates complex adaptive behaviour in plant communities. AoB Plants 7. Oxford Academic.</ref> Through root systems and common mycorrhizal networks, plants are able to communicate with one another below ground and alter behaviors or even share nutrients depending on different environmental cues.

==Acoustic communication==
Recent works have shown that plants can respond to airborne sounds at audible frequencies <ref>Veits, M., Khait, I., Obolski, U., Zinger, E., Boonman, A., Goldshtein, A., Saban, K., Seltzer, R., Ben-Dor, U., Estlein, P., Kabat, A., Peretz, D., Ratzersdorfer, I., Krylov, S., Chamovitz, D., Sapir, Y., Yovel, Y. and Hadany, L. (2019), Flowers respond to pollinator sound within minutes by increasing nectar sugar concentration. Ecol Lett, 22: 1483-1492. https://doi.org/10.1111/ele.13331</ref> and that they also produce airborne sounds at the [[Ultrasound|ultrasonic]] range (for example, tomato and tobacco plants when cut with scissors), presumably audible to multiple organisms including bats, mice, moths and other insects.<ref>Khait I, Lewin-Epstein O, Sharon R, Saban K, Goldstein R, Anikster Y, Zeron Y, Agassy C, Nizan S, Sharabi G, Perelman R, Boonman A, Sade N, Yovel Y, Hadany L. Sounds emitted by plants under stress are airborne and informative. Cell. 2023 Mar 30;186(7):1328-1336.e10. doi: 10.1016/j.cell.2023.03.009. PMID 37001499.</ref>

==See also==
*[[Biosemiotics]]
*[[Phytosemiotics]]
*[[Plant defense against herbivory]]

==References==
{{reflist}}

==Further reading==
* {{cite book |title=The Hidden Life of Trees: What They Feel, How They Communicate―Discoveries from A Secret World |year=2016 |author=Peter Wohlleben |translator=Jane Billinghurst |author3=Tim Flannery |author2= Suzanne Simard |publisher=Greystone Books |isbn=978-1771642484}}

[[Category:Plant communication| ]]
[[Category:Communication]]
[[Category:Plant physiology]]
[[Category:Chemical ecology]]