Editing Stoma (section)

==Development==
There are three major epidermal cell types which all ultimately derive from the outermost (L1) tissue layer of the [[shoot apical meristem]], called protodermal cells: [[trichome]]s, [[pavement cells]] and guard cells, all of which are arranged in a non-random fashion.

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 name="Bergmann-2004">{{Cite journal|last1=Bergmann|first1=Dominique C.; Lukowitz, Wolfgang; Somerville, Chris R.|last2=Lukowitz|first2=W|last3=Somerville|first3=CR|date=4 July 2004|title=Stomatal Development and Pattern Controlled by a MAPKK Kinase|url=http://www.sciencemag.org/cgi/content/ful/304/5676/1494/DC1|journal=Science|volume=304|issue=5676|pages=1494–1497|doi=10.1126/science.1096014|pmid=15178800|bibcode=2004Sci...304.1494B|s2cid=32009729}}</ref> Cell division is inhibited in some cells so there is always at least one cell between stomata.<ref name="Pillitteri-2013">{{Cite journal|last1=Pillitteri|first1=Lynn Jo|last2=Dong|first2=Juan|date=2013-06-06|title=Stomatal Development in Arabidopsis|journal=The Arabidopsis Book|volume=11|page=e0162|doi=10.1199/tab.0162|issn=1543-8120|pmc=3711358|pmid=23864836}}</ref>

Stomatal patterning is controlled by the interaction of many [[signal transduction]] components such as ''EPF'' (Epidermal Patterning Factor), ''ERL'' (ERecta Like) and ''YODA'' (a putative [[MAP kinase kinase kinase]]).<ref name="Pillitteri-2013" /> Mutations in any one of the genes which encode these factors may alter the development of stomata in the epidermis.<ref name="Pillitteri-2013" /> For example, a mutation in one gene causes more stomata that are clustered together, hence is called Too Many Mouths (''TMM'').<ref name="Bergmann-2004" /> Whereas, disruption of the ''SPCH'' (SPeecCHless) gene prevents stomatal development all together.<ref name="Pillitteri-2013" /> &nbsp;Inhibition of stomatal production can occur by the activation of EPF1, which activates TMM/ERL, which together activate YODA. YODA inhibits SPCH, causing SPCH activity to decrease, preventing asymmetrical cell division that initiates stomata formation.<ref name="Pillitteri-2013" /><ref>{{Cite journal|last1=Casson|first1=Stuart A|last2=Hetherington|first2=Alistair M|date=2010-02-01|title=Environmental regulation of stomatal development|journal=Current Opinion in Plant Biology|volume=13|issue=1|pages=90–95|doi=10.1016/j.pbi.2009.08.005|pmid=19781980|bibcode=2010COPB...13...90C }}</ref> Stomatal development is also coordinated by the cellular peptide signal called stomagen, which signals the activation of the SPCH, resulting in increased number of stomata.<ref>{{Cite journal|last1=Sugano|first1=Shigeo S.|last2=Shimada|first2=Tomoo|last3=Imai|first3=Yu|last4=Okawa|first4=Katsuya|last5=Tamai|first5=Atsushi|last6=Mori|first6=Masashi|last7=Hara-Nishimura|first7=Ikuko|date=2010-01-14|title=Stomagen positively regulates stomatal density in Arabidopsis|journal=Nature|language=en|volume=463|issue=7278|pages=241–244|doi=10.1038/nature08682|pmid=20010603|issn=0028-0836|bibcode=2010Natur.463..241S|hdl=2433/91250|s2cid=4302041|hdl-access=free}}</ref>

Environmental and hormonal factors can affect stomatal development. Light increases stomatal development in plants; while, plants grown in the dark have a lower amount of stomata. [[Auxin]] represses stomatal development by affecting their development at the receptor level like the ERL and TMM receptors. However, a low concentration of auxin allows for equal division of a guard mother cell and increases the chance of producing guard cells.<ref>{{cite journal | last1 = Balcerowicz | first1 = M. | last2 = Ranjan | first2 = A. | last3 = Rupprecht | first3 = L. | last4 = Fiene | first4 = G. | last5 = Hoecker | first5 = U. | year = 2014 | title = Auxin represses stomatal development in dark-grown seedling via Aux/IAA proteins | journal = Development | volume = 141 | issue = 16| pages = 3165–3176 | doi=10.1242/dev.109181| pmid = 25063454 | doi-access = free }}</ref>

Most [[angiosperm trees]] have stomata only on their lower leaf surface. [[Populus|Poplars]] and [[willows]] have them on both surfaces. When leaves develop stomata on both leaf surfaces, the stomata on the lower surface tend to be larger and more numerous, but there can be a great degree of variation in size and frequency about species and genotypes. [[Fraxinus americana|White ash]] and [[white birch]] leaves had fewer stomata but larger in size. On the other hand [[sugar maple]] and [[silver maple]] had small stomata that were more numerous.<ref>{{cite journal |last1=Pallardy |first1=Stephen |title=Physiology of Woody Plants |journal=Journal of Applied Ecology |date=1983 |volume=20 |issue=1 |page=14|doi=10.2307/2403413 |jstor=2403413 |bibcode=1983JApEc..20..352J }}</ref>