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| {{for|natural and surgically created body openings|Stoma (medicine)}}
| | Let me initial begin by introducing myself. My name is Boyd Butts although it is not the title on my birth certificate. California is our beginning place. Hiring is his occupation. The factor she adores most is physique building and now she is trying to earn cash with it.<br><br>My website: at home std testing [[http://Www.pierrecardin.by/autoimmune-diseases-information-on-autoimmune-diseases Read More On this page]] |
| {{mergefrom|Guard cell|date=April 2013}}
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| [[File:Tomato leaf stomate 1-color.jpg|300px|thumb|Stoma in a [[tomato]] leaf shown via colorized [[scanning electron microscope]] image]]
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| [[File:HPIM0188-ligusterblad.jpg|thumb|300px|A stoma in cross section]]
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| [[File:LeafUndersideWithStomata.jpg|thumb|300px|right|The underside of a leaf. In this species (''Tradescantia zebrina'') the stomata appear green (due to chlorophyll) while the epidermal cells appear red due to additional pigmentation.]]
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| In [[botany]], a '''stoma''' (plural ''stomata'') (occasionally called a stomate, plural stomates)<ref>{{cite web|title=Living Environment—Regents High school examination|url=http://www.nysedregents.org/LivingEnvironment/Archive/20110125-le-examrev.pdf|work=January 2011 Regents|publisher=NYSED|accessdate=15 June 2013}}</ref> (from [[Greek language|Greek]] [[wikt:στόμα|στόμα]], "mouth"<ref>[http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dsto%2Fma στόμα], Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus</ref>) is a pore, found in the epidermis of leaves, stems and other organs that is used to control [[gas exchange]]. The pore is bordered by a pair of specialized [[parenchyma]] cells known as [[guard cell]]s that are responsible for regulating the size of the opening. The term is also used collectively to refer to an entire stomatal complex, both the pore itself and its accompanying guard cells.<ref name="Esau">{{cite book | last=Esau | first=K. | year=1977 | title=Anatomy of Seed Plants | publisher=Wiley and Sons | page=88 | isbn=0-471-24520-8 }}</ref> Air containing [[carbon dioxide]] and [[oxygen]] enters the plant through these openings and is used in [[photosynthesis]] in the '''[[leaf#mesophyll|mesophyll]]''' cells (parenchyma cells with [[chloroplast]]s) and [[Cellular respiration|respiration]], respectively. Oxygen produced as a by-product of photosynthesis diffuses out to the atmosphere through these same openings. Also, [[water vapor]] is released into the atmosphere through these pores in a process called [[transpiration]].
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| Stomata are present in the [[sporophyte]] generation of all [[land plant]] groups except [[Marchantiophyta|liverworts]]. [[Dicotyledons]] usually have more stomata on the lower [[epidermis (botany)|epidermis]] than the upper epidermis. [[Monocotyledons]], on the other hand, usually have the same number of stomata on the two epidermes. In plants with floating leaves, stomata may be found only on the upper epidermis; submerged leaves may lack stomata entirely.
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| ==Function==
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| [[File:Stoma with Accompanying Guard Cells.jpg|thumb|This is an electron micrograph of a stoma from a Brassica chinensis (Bok Choy) leaf.]]
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| ===CO<sub>2</sub> gain and water loss===
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| Carbon dioxide, a key reactant in photosynthesis, is present in the atmosphere at a concentration of about 390 ppm (as of December 2011). Most plants require the stomata to be open during daytime. The problem is that the air spaces in the leaf are saturated with water vapour, which exits the leaf through the stomata (this is known as [[transpiration]]). Therefore, plants cannot gain carbon dioxide without simultaneously losing water vapour.<ref>Debbie Swarthout and C.Michael Hogan. 2010. [http://www.eoearth.org/article/Stomata ''Stomata''. Encyclopedia of Earth]. National Council for Science and the Environment, Washington DC</ref>
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| ===Alternative approaches===
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| Ordinarily, carbon dioxide is fixed to [[ribulose-1,5-bisphosphate]] (RuBP) by the enzyme [[RuBisCO]] in mesophyll cells exposed directly to the air spaces inside the leaf. This exacerbates the transpiration problem for two reasons: first, RuBisCo has a relatively low affinity for carbon dioxide, and second, it fixes oxygen to RuBP, wasting energy and carbon in a process called [[photorespiration]]. For both of these reasons, RuBisCo needs high carbon dioxide concentrations, which means wide stomatal apertures and, as a consequence, high water loss.
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| Narrower stomatal apertures can be used in conjunction with an intermediary molecule with a high carbon dioxide affinity, PEPcase ([[Phosphoenolpyruvate carboxylase]]). Retrieving the products of carbon fixation from PEPCase is in an energy-intensive process, however. As a result, the PEPCase alternative is preferable only where water is limiting but light is plentiful, or where high temperatures increase the solubility of oxygen relative to that of carbon dioxide, magnifying RuBisCo's oxygenation problem.
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| ===CAM plants===
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| A group of mostly desert plants called "CAM" plants ([[Crassulacean acid metabolism]], after the family Crassulaceae, which includes the species in which the CAM process was first discovered) open their stomata at night (when water evaporates more slowly from leaves for a given degree of stomatal opening), use PEPcarboxylase to fix carbon dioxide and store the products in large vacuoles. The following day, they close their stomata and release the carbon dioxide fixed the previous night into the presence of [[RuBisCO]]. This saturates RuBisCO with carbon dioxide, allowing minimal photorespiration. This approach, however, is severely limited by the capacity to store fixed carbon in the vacuoles, so it is preferable only when water is severely limiting.
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| ===Opening and closure===
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| {{details|Guard cell}}
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| [[File:Stoma Opening Closing.svg|thumb|An open stoma (a) and a closed stoma (b)<br />
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| 1 [[Epidermis (botany)|Epidermal cell]]<br />
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| 2 [[Guard cell]]
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| <br />
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| 3 Stoma
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| <br />
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| 4 K+ ions
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| <br />
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| 5 Water
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| <br />
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| 6 [[Vacuole]]]]
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| However, most plants do not have the aforementioned facility and must therefore open and close their stomata during the daytime in response to changing conditions, such as light intensity, humidity, and carbon dioxide concentration. It is not entirely certain how these responses work. However, the basic mechanism involves regulation of osmotic pressure.
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| When conditions are conducive to stomatal opening (e.g., high light intensity and high humidity), a [[proton pump]] drives [[protons]] (H<sup>+</sup>) from the [[guard cell]]s. This means that the cells' [[electrical potential]] becomes increasingly negative. The negative potential opens potassium voltage-gated channels and so an uptake of [[potassium]] ions (K<sup>+</sup>) occurs. To maintain this internal negative voltage so that entry of potassium ions does not stop, negative ions balance the influx of potassium. In some cases, chloride ions enter, while in other plants the organic ion malate is produced in guard cells. This increase in solute concentration lowers the [[water potential]] inside the cell, which results in the diffusion of water into the cell through [[osmosis]]. This increases the cell's volume and [[osmotic pressure|turgor pressure]]. Then, because of rings of cellulose [[microfibrils]] that prevent the width of the guard cells from swelling, and thus only allow the extra turgor pressure to elongate the guard cells, whose ends are held firmly in place by surrounding [[epidermis (botany)|epidermal]] cells, the two guard cells lengthen by bowing apart from one another, creating an open pore through which gas can move.<ref>{{cite journal
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| |journal=Annals of Botany
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| |volume=89
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| |issue=1
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| |date=January 2002
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| |pages=23–29
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| |title=Structure and Development of Stomata on the Primary Root of ''Ceratonia siliqua'' L.
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| |author=N. S. CHRISTODOULAKIS
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| |coauthors=J. MENTI and B. GALATIS
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| |pmid=12096815 | doi = 10.1093/aob/mcf002
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| }}</ref>
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| When the roots begin to sense a water shortage in the soil, [[abscisic acid]] (ABA) is released.<ref>{{cite journal
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| |journal=Plant Physiology
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| |volume=102
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| |issue=2
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| |year=1993
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| |pages=497–502
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| |title=Sensitivity of Stomata to Abscisic Acid (An Effect of the Mesophyll)
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| |author=C. L. Trejo
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| |coauthors=W. J. Davies; LdMP. Ruiz
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| |pmid=12231838
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| |pmc=158804 }}</ref> ABA binds to receptor proteins in the guard cells' plasma membrane and cytosol, which first raises the pH of the [[cytosol]] of the cells and cause the concentration of free Ca<sup>2+</sup> to increase in the cytosol due to influx from outside the cell and release of Ca<sup>2+</sup> from internal stores such as the endoplasmic reticulum and vacuoles.<ref>{{cite journal
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| |journal=Journal of Experimental Botany
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| |volume=52
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| |issue=363
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| |pages=1959–1967
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| |date=October 2001
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| |title=The role of ion channels in light-dependent stomatal opening
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| |author=Petra Dietrich
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| |coauthors=Dale Sanders; Rainer Hedrich
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| |pmid=11559731
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| |doi=10.1093/jexbot/52.363.1959 }}</ref> This causes the chloride (Cl<sup>-</sup>) and inorganic ions to exit the cells. Second, this stops the uptake of any further K<sup>+</sup> into the cells and, subsequently, the loss of K<sup>+</sup>. The loss of these solutes causes an increase in [[water potential]], which results in the diffusion of water back out of the cell by [[osmosis]]. This makes the cell [[plasmolysed]], which results in the closing of the stomatal pores.
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| Guard cells have more chloroplasts than the other epidermal cells from which guard cells are derived. Their function is controversial.<ref>{{cite web |url=http://4e.plantphys.net/article.php?ch=&id=265 |title=Guard Cell Photosynthesis |accessdate=2007-04-29 |format= |work= }}</ref><ref>{{cite journal
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| |title=The Guard Cell Chloroplast: A Perspective for the Twenty-First Century
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| |author=Eduardo Zeiger
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| |coauthors=Lawrence D. Talbott; Silvia Frechilla; Alaka Srivastava; Jianxin Zhu
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| |journal=New Phytologist
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| |volume=153
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| |issue=3 Special Issue: Stomata
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| |date=March 2002
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| |pages=415–424
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| |doi=10.1046/j.0028-646X.2001.NPH328.doc.x
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| }}</ref>
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| ===Inferring stomatal behavior from gas exchange===
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| The degree of stomatal resistance can be determined by measuring leaf gas exchange of a leaf. The [[transpiration]] rate is dependent on the [[diffusion]] resistance provided by the stomatal pores, and also on the [[humidity]] gradient between the leaf's internal air spaces and the outside air. Stomatal resistance (or its inverse, stomatal conductance) can therefore be calculated from the transpiration rate and humidity gradient. This allows scientists to investigate how stomata respond to changes in environmental conditions, such as light intensity and concentrations of gases such as water vapor, carbon dioxide, and [[ozone]].<ref>{{cite journal |url=http://www.nature.com/nature/journal/v448/n7152/full/448396b.html |first=Michael |last=Hopkin |title=Carbon sinks threatened by increasing ozone |journal=Nature |volume=448 |pages=396–397 |date=2007-07-26 |bibcode=2007Natur.448..396H |doi=10.1038/448396b |issue=7152}}</ref> Evaporation (''E'') can be calculated as;<ref name=calculations>{{cite web |url=http://4e.plantphys.net/article.php?ch=9&id=134 |title=Calculating Important Parameters in Leaf Gas Exchange |work=Plant Physiology Online|publisher=Sinauer |accessdate=2013-02-24}}</ref>
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| <math> E = (e_{i} - e_{a})/Pr</math>
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| where ''e''<sub>i</sub> and ''e''<sub>a</sub> are the partial pressures of water in the leaf and in the ambient air, respectively, ''P'' is atmospheric pressure, and ''r'' is stomatal resistance.
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| The inverse of ''r'' is conductance to water vapor (''g''), so the equation can be rearranged to;<ref name=calculations/>
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| <math>E = (e_{i} - e_{a})g/P</math>
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| and solved for ''g'';<ref name=calculations/>
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| <math>g = EP / (e_{i} - e_{a})</math>
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| Photosynthetic CO<sub>2</sub> assimilation (''A'') can be calculated from
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| <math>A = (C_{a} - C_{i})g/1.6P</math>
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| where ''C''<sub>a</sub> and ''C''<sub>i</sub> are the atmospheric and sub-stomatal partial pressures of CO<sub>2</sub>, respectively. The rate of evaporation from a leaf can be determined using a [[photosynthesis system]]. These scientific instruments measure the amount of water vapour leaving the leaf and the vapor pressure of the ambient air. Photosynthetic systems may calculate [[water use efficiency]] (''A/E''), ''g'', intrinsic water use efficiency (''A/g''), and ''C''<sub>i</sub>. These scientific instruments are commonly used by plant physiologists to measure CO<sub>2</sub> uptake and thus measure photosynthetic rate.<ref>{{cite journal
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| |journal=Photosynthesis Research
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| |volume=9
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| |issue=3
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| |date=January 1986
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| |pages=345–357
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| |title=A system for measuring leaf gas exchange based on regulating vapour pressure difference
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| |author=Waichi Agata
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| |author2=Yoshinobu Kawamitsu
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| |author3=Susumu Hakoyama
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| |author4=Yasuo Shima
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| |doi=10.1007/BF00029799
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| |issn=1573-5079
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| |url=http://www.springerlink.com/content/kgk602r755725428/?p=edcd9d6d27f24b7da928dc3c60d9eebf&pi=0
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| |accessdate=May 6, 2010
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| |pmid=24442366
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| }}</ref>
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| ==Stomata and Climate Change==
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| ===Response of Stomata to Environmental Factors===
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| [[Photosynthesis]], plant water transport ([[xylem]]) and gas exchange are regulated by stomatal function which is important in the functioning of plants.<ref name=":0">Rico, C, Pittermann, J, Polley, H, W, Aspinwall, M, J, and Fay, P, A 2013, ‘The effect of subambient to elevated atmospheric CO2 concentration on vascular function in Helianthus annuus: implications for plant response to climate change’, ''New Phytologist'', vol. 199, pp. 956-965</ref> Stomatal density and aperture (length of stomata) varies under a number of environmental factors such as atmospheric CO<sub>2</sub> concentration, light intensity, air temperature and photoperiod (daytime duration).
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| <ref name=":1">Buckley, T, N, and Mott, K, A 2013, ‘Modelling stomatal conductance in response to environmental factors’, Plant, ''Cell and Environment'', vol. 36, pp. 1691-1699</ref><ref name=":2">Rogiers, S, Y, Hardie, W, J, and Smith, J, P 2011, ‘Stomatal density of grapevine leaves (Vitis Vinifera L.) responds to soil temperature and atmospheric carbon dioxide, ''Australian Journal of Grape and Wine Research'', vol. 17, pp. 147–152</ref>
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| Decreasing stomatal density is one way plants have responded to the increase in concentration of atmospheric CO<sub>2</sub> ([CO<sub>2</sub>]<sub>atm</sub>).<ref name=":3">Ceccarelli, S, Grando, S, Maatougui, M, Michael, M, Slash, M, Haghparast, R, Rahmanian, M, Taheri, A, Al-Yassin, A, Benbelkacem, A, Labdi, M, Mimoun, H & Nachit, M 2010, 'Plant breeding and climate changes', ''The Journal of Agricultural Science'', vol. 148, no. 06, pp. 627–637
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| </ref> Although changes in [CO<sub>2</sub>]<sub>atm</sub> response is the least understood mechanistically, this stomatal response has begun to plateau where it is soon expected to impact [[transpiration]] and [[photosynthesis]] processes in plants.<ref name=":0" /><ref>Serna, L, and Fenoll, C 2000, ‘Coping with human CO2 emissions’, ''Nature'', vol. 408, pp. 656–657</ref>
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| ===Future Adaptations during Climate Change===
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| It is expected for [CO<sub>2</sub>]<sub>atm</sub> to reach 500-1000 ppm by 2100.<ref name=":0" /> 96% of the past 400 000 years experienced below 280 ppm CO<sub>2</sub> levels. From this figure, it is highly probable that [[genotype]]s of today’s plants diverged from their pre-industrial relative.
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| <ref name=":0" />
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| The gene ''HIC'' (high carbon dioxide) encodes a negative regulator for the development of stomata in plants.<ref name=":4">Gray, J, E, Holroyd, G, H, van der Lee, F, M, Bahrami, A, R, Sijmons, P, C, Woodward, F, I, Schuch, W, and Hetherington, A, M 2000, ‘The ''HIC'' signalling pathway links CO<sub>2</sub> perception to stomatal development’, ''Nature'', vol. 408, pp. 713–716</ref> Research into the ''HIC'' gene using'' [[Arabidopsis thaliana]]'' found no increase of stomatal development in the dominant [[allele]], but in the ‘wild type’ [[recessive allele]] showed a large increase, both in response to rising CO<sub>2</sub> levels in the atmosphere.<ref name=":4" /> These studies imply the plants response to changing CO<sub>2</sub> levels is largely controlled by genetics.
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| ===Agricultural Implications===
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| In the face of ecological contingencies such as increasing temperatures, changes in rainfall patterns, long term climate change, and [[wikt:biotic|biotic]] influences of human management interventions, it is expected to reduce the production and quality of food and have a negative impact on agricultural production.
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| <ref name=":2" /><ref name=":3" />
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| The CO<sub>2 </sub>fertiliser effect has been greatly overestimated during [[Free-air concentration enrichment|Free-Air Carbon dioxide Enrichment]] (FACE) experiments where results show increased CO<sub>2</sub> levels in the atmosphere enhances photosynthesis, reduce transpiration, and increase [[Water-use efficiency|water use efficiency]] (WUE).<ref name=":3" /> Increased [[biomass]] is one of the effects with simulations from experiments predicting a 5–20% increase in crop yields at 550 ppm of CO<sub>2</sub>.<ref name=":5">Tubiello, F, N, Soussana, J-F, Howden, S, M 2007, ‘Crop and pasture response to climate change’, ''Proceedings of the National Academy of Sciences of the United States of America'', vol. 104, no. 50, pp. 19686–19690</ref> Rates of leaf photosynthesis were shown to increase by 30-50% in [[C3 carbon fixation|C3]] plants, and 10-25% in [[C4 carbon fixation|C4]] under doubled CO<sub>2</sub> levels.<ref name=":5" /> The existence of a [[feedback mechanism]] results a [[phenotypic plasticity]] in response to [CO<sub>2</sub>]<sub>atm</sub> that may have been an adaptive trait in the evolution of plant respiration and function.<ref name=":0" /><ref name=":2" />
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| Predicting how stomata performs during adaptation is useful for understanding the productivity of plant systems for both natural and [[agricultural systems]].<ref name=":1" /> Plant breeders and farmers are beginning to work together using evolutionary and participatory plant breeding to find the best suited species such as heat and drought resistant crop varieties that could naturally evolve to the change in the face of food security challenges.<ref name=":3" />
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| ==Evolution==
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| [[File:Tomato stoma observed through immersion oil.gif|thumbnail|left|Tomato stoma observed through immersion oil]]
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| The fossil record has little to say about the evolution of stomata.<ref>{{Cite journal
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| | last1 = D. Edwards | first1 = H. Kerp
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| | last2 = Hass | first2 = H.
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| | year = 1998
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| | title = Stomata in early land plants: an anatomical boka and ecophysiological approach
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| | journal = Journal of Experimental Botany
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| | volume = 49
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| | pages = 255–278
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| | doi = 10.1093/jexbot/49.suppl_1.255
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| | postscript = <!--None-->
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| | issue = 90001
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| }}</ref> They may have evolved by the modification of [[conceptacles]] from plants' alga-like ancestors.<ref>{{cite book
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| | last = Krassilov | first = Valentin A.
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| | chapter = Macroevolutionary events and the origin of higher taxa
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| | pages=265–289
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| | chapterurl=http://books.google.co.uk/books?hl=en&lr=&ie=UTF-8&id=tJeZC885-OcC&oi=fnd&pg=PA265&ots=at1Bka6ZfT&sig=fximfLOKQG6SeTQDhhAl8076BDM
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| | isbn = 1-4020-1693-X
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| | editor-first = Solomon P.
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| | editor-last= Wasser
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| | year = 2004
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| | publisher = Kluwer Acad. Publ.
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| | location = Dordrecht
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| | title = Evolutionary theory and processes : modern horizons : papers in honour of Eviatar Nevo }}</ref>
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| It is clear, however, that the evolution of stomata must have happened at the same time as the waxy [[Plant cuticle|cuticle]] was evolving – these two traits together constituted a major advantage for early terrestrial plants.
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| ==Development==
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| There are three major epidermal cell types which all ultimately derive from the L1 tissue layer of the [[shoot apical meristem]], called protodermal cells: [[trichome]]s, [[pavement cells]] and [[guard cell]]s, all of which are arranged in a non-random fashion.
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| Production is reliant on interactions between SPCH (speechless), EPF (downregulates stomata), TMM (too many mouths, downregulates stomata) and stomagen (upregulates stomata, inhibits SPCH), ERL and YODA downregulate stomata too.
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| Stomata positioning is down to CO2 activating EPF1, which activates TMM/ERL which together activate YODA, YODA in turn inhibits SPCH, in turn SPCH activation decreases, allowing asymmetry.
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| An asymmetrical cell division occurs in protodermal cells resulting in one large cell that is fated to become a pavement cell and a smaller cell called a meristemoid that will eventually differentiate into the guard cells that surround a stoma. This meristemoid then divides asymmetrically one to three times before differentiating into a guard mother cell. The guard mother cell then makes one symmetrical division, which forms a pair of guard cells.<ref>{{Cite journal| title=Stomatal Development and Pattern Controlled by a MAPKK Kinase| last=Bergmann| first=Dominique C.; Lukowitz, Wolfgang; Somerville, Chris R.| journal=Science| volume=304| date=4 July 2004| url=http://www.sciencemag.org/cgi/content/ful/304/5676/1494/DC1| pages=1494–1497| doi=10.1126/science.1096014| pmid=15178800| last2=Lukowitz| first2=W| last3=Somerville| first3=CR| issue=5676| postscript=<!--None-->}}</ref>
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| ==Stomata as pathogenic pathways==
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| Stomata are an obvious hole in the leaf by which, as was presumed for a while, pathogens can enter unchallenged. However, it has been recently shown that stomata do in fact sense the presence of some, if not all, pathogens. However, with the virulent bacteria applied to [[Arabidopsis thaliana|''Arabidopsis'']] plant leaves in the experiment, the bacteria released the chemical [[coronatine]], which forced the stomata open again within a few hours.<ref>{{cite journal
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| |journal=Cell
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| |volume=126
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| |pages=969–980
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| |date=September 2006
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| |title=Plant Stomata Function in Innate Immunity against Bacterial Invasion
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| |author=Maeli Melotto
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| |coauthors=William Underwood, Jessica Koczan, Kinya Nomura, Sheng Yang He
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| |doi=10.1016/j.cell.2006.06.054|pmid=16959575
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| |issue=5}}</ref>
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| ==References==
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| {{commons category}}
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| {{reflist}}
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| {{-}}
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| {{Botany}}
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| [[Category:Photosynthesis]]
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| [[Category:Plant physiology]]
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| [[Category:Plant anatomy]]
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| [[Category:Plant cells]]
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| {{Link GA|cs}}
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