Editing Action potential (section)

===Plant action potentials===
{{See also|Variation potential}}

[[Plant cells|Plant]] and [[fungi|fungal cells]]<ref name="Slayman_1976" group=lower-alpha>{{cite journal | vauthors = Slayman CL, Long WS, Gradmann D | title = "Action potentials" in Neurospora crassa, a mycelial fungus | journal = Biochimica et Biophysica Acta (BBA) - Biomembranes | volume = 426 | issue = 4 | pages = 732–44 | date = April 1976 | pmid = 130926 | doi = 10.1016/0005-2736(76)90138-3 }}</ref> are also electrically excitable. The fundamental difference from animal action potentials is that the depolarization in plant cells is not accomplished by an uptake of positive sodium ions, but by release of negative ''chloride'' ions.<ref name = "Mummert_1991" group=lower-alpha>{{cite journal | vauthors = Mummert H, Gradmann D | title = Action potentials in Acetabularia: measurement and simulation of voltage-gated fluxes | journal = The Journal of Membrane Biology | volume = 124 | issue = 3 | pages = 265–73 | date = December 1991 | pmid = 1664861 | doi = 10.1007/BF01994359 | s2cid = 22063907 }}</ref><ref name = "Gradmann_2001" group=lower-alpha>{{cite journal | vauthors = Gradmann D | year = 2001 | title = Models for oscillations in plants | journal = Aust. J. Plant Physiol. | volume = 28 | issue = 7 | pages = 577–590 | doi = 10.1071/pp01017}}</ref><ref name = "Beilby_2007" group=lower-alpha>{{cite book | vauthors = Beilby MJ | title = Action Potential in Charophytes | volume = 257 | pages = 43–82 | year = 2007 | pmid = 17280895 | doi = 10.1016/S0074-7696(07)57002-6 | isbn = 978-0-12-373701-4 | series = International Review of Cytology }}</ref> In 1906, J. C. Bose published the first measurements of action potentials in plants, which had previously been discovered by Burdon-Sanderson and Darwin.<ref>{{Cite journal|last=Tandon|first=Prakash N|date=2019-07-01|title=Jagdish Chandra Bose and Plant Neurobiology: Part I|url=http://insa.nic.in/writereaddata/UpLoadedFiles/IJHS/Vol54_2_2019__Art05.pdf|journal=Indian Journal of History of Science|volume=54|issue=2|doi=10.16943/ijhs/2019/v54i2/49660|issn=0019-5235|doi-access=free}}</ref> An increase in cytoplasmic calcium ions may be the cause of anion release into the cell. This makes calcium a precursor to ion movements, such as the influx of negative chloride ions and efflux of positive potassium ions, as seen in barley leaves.<ref>{{cite journal | vauthors = Felle HH, Zimmermann MR | title = Systemic signalling in barley through action potentials | journal = Planta | volume = 226 | issue = 1 | pages = 203–14 | date = June 2007 | pmid = 17226028 | doi = 10.1007/s00425-006-0458-y | bibcode = 2007Plant.226..203F | s2cid = 5059716 }}</ref>

The initial influx of calcium ions also poses a small cellular depolarization, causing the voltage-gated ion channels to open and allowing full depolarization to be propagated by chloride ions.

Some plants (e.g. ''[[Dionaea muscipula]]'') use sodium-gated channels to operate plant movements and "count" stimulation events to determine if a threshold for movement is met. ''Dionaea muscipula'', also known as the Venus flytrap, is found in subtropical wetlands in North and South Carolina.<ref>{{Cite journal|last=Luken|first=James O. | name-list-style = vanc |date= December 2005 |title=Habitats of Dionaea muscipula (Venus' Fly Trap), Droseraceae, Associated with Carolina Bays|journal=Southeastern Naturalist|language=en|volume=4|issue=4|pages=573–584|doi=10.1656/1528-7092(2005)004[0573:HODMVF]2.0.CO;2|s2cid=9246114 |issn=1528-7092}}</ref> When there are poor soil nutrients, the flytrap relies on a diet of insects and animals.<ref name=":1">{{cite journal | vauthors = Böhm J, Scherzer S, Krol E, Kreuzer I, von Meyer K, Lorey C, Mueller TD, Shabala L, Monte I, Solano R, Al-Rasheid KA, Rennenberg H, Shabala S, Neher E, Hedrich R | display-authors = 6 | title = The Venus Flytrap Dionaea muscipula Counts Prey-Induced Action Potentials to Induce Sodium Uptake | journal = Current Biology | volume = 26 | issue = 3 | pages = 286–95 | date = February 2016 | pmid = 26804557 | pmc = 4751343 | doi = 10.1016/j.cub.2015.11.057 | bibcode = 2016CBio...26..286B }}</ref> Despite research on the plant, there lacks an understanding behind the molecular basis to the Venus flytraps, and carnivore plants in general.<ref name=":2">{{cite journal | vauthors = Hedrich R, Neher E | title = Venus Flytrap: How an Excitable, Carnivorous Plant Works | journal = Trends in Plant Science | volume = 23 | issue = 3 | pages = 220–234 | date = March 2018 | pmid = 29336976 | doi = 10.1016/j.tplants.2017.12.004 | bibcode = 2018TPS....23..220H }}</ref>

However, plenty of research has been done on action potentials and how they affect movement and clockwork within the Venus flytrap. To start, the resting membrane potential of the Venus flytrap (−120&nbsp;mV) is lower than animal cells (usually −90&nbsp;mV to −40&nbsp;mV).<ref name=":2" /><ref>Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. Electrical Potentials Across Nerve Cell Membranes. Available from: [https://www.ncbi.nlm.nih.gov/books/NBK11069/]</ref> The lower resting potential makes it easier to activate an action potential. Thus, when an insect lands on the trap of the plant, it triggers a hair-like mechanoreceptor.<ref name=":2" /> This receptor then activates an action potential that lasts around 1.5&nbsp;ms.<ref>{{cite journal | vauthors = Volkov AG, Adesina T, Jovanov E | title = Closing of venus flytrap by electrical stimulation of motor cells | journal = Plant Signaling & Behavior | volume = 2 | issue = 3 | pages = 139–45 | date = May 2007 | pmid = 19516982 | pmc = 2634039 | doi = 10.4161/psb.2.3.4217 | bibcode = 2007PlSiB...2..139V }}</ref> This causes an increase of positive calcium ions into the cell, slightly depolarizing it. However, the flytrap does not close after one trigger. Instead, it requires the activation of two or more hairs.<ref name=":1" /><ref name=":2" /> If only one hair is triggered, it disregards the activation as a false positive. Further, the second hair must be activated within a certain time interval (0.75–40&nbsp;s) for it to register with the first activation.<ref name=":2" /> Thus, a buildup of calcium begins and then slowly falls after the first trigger. When the second action potential is fired within the time interval, it reaches the calcium threshold to depolarize the cell, closing the trap on the prey within a fraction of a second.<ref name=":2" />

Together with the subsequent release of positive potassium ions the action potential in plants involves an [[osmotic]] loss of salt (KCl). Whereas, the animal action potential is osmotically neutral because equal amounts of entering sodium and leaving potassium cancel each other osmotically. The interaction of electrical and osmotic relations in plant cells<ref name="Gradmann_1998" group="lower-alpha">{{cite journal | vauthors = Gradmann D, Hoffstadt J | title = Electrocoupling of ion transporters in plants: interaction with internal ion concentrations | journal = The Journal of Membrane Biology | volume = 166 | issue = 1 | pages = 51–9 | date = November 1998 | pmid = 9784585 | doi = 10.1007/s002329900446 | s2cid = 24190001 }}</ref> appears to have arisen from an osmotic function of electrical excitability in a common unicellular ancestors of plants and animals under changing salinity conditions. Further, the present function of rapid signal transmission is seen as a newer accomplishment of [[metazoan]] cells in a more stable osmotic environment.<ref name="Gradmann_1980">
Gradmann, D; Mummert, H in {{harvnb|Spanswick|Lucas|Dainty|1980|loc=''Plant action potentials'', pp. 333–344.}}</ref> It is likely that the familiar signaling function of action potentials in some vascular plants (e.g. ''[[Mimosa pudica]]'') arose independently from that in metazoan excitable cells.

Unlike the rising phase and peak, the falling phase and after-hyperpolarization seem to depend primarily on cations that are not calcium. To initiate repolarization, the cell requires movement of potassium out of the cell through passive transportation on the membrane. This differs from neurons because the movement of potassium does not dominate the decrease in membrane potential. To fully repolarize, a plant cell requires energy in the form of ATP to assist in the release of hydrogen from the cell – utilizing a transporter called [[proton ATPase]].<ref name="Opritov">Opritov, V A, et al. "Direct Coupling of Action Potential Generation in Cells of a Higher Plant (Cucurbita Pepo) with the Operation of an Electrogenic Pump." ''Russian Journal of Plant Physiology'', vol. 49, no. 1, 2002, pp. 142–147.</ref><ref name=":2" />