Editing Root (section)

==Growth==
[[File:Root of a Tree.JPG|thumb|Roots of trees]]
Early root growth is one of the functions of the '''apical meristem''' located near the tip of the root. The meristem cells more or less continuously divide, producing more meristem, [[root cap]] cells (these are sacrificed to protect the meristem), and undifferentiated root cells. The latter become the primary tissues of the root, first undergoing elongation, a process that pushes the root tip forward in the growing medium. Gradually these cells differentiate and mature into specialized cells of the root tissues.<ref name="Russell Hertz McMillan 2013">{{cite book | vauthors = Russell PJ, Hertz PE, McMillan B | title=Biology: The Dynamic Science | publisher=Cengage Learning | year=2013 | isbn=978-1-285-41534-5 | url=https://books.google.com/books?id=dVIWAAAAQBAJ&pg=PT1365 | access-date=2017-04-24 | page=750 | url-status=live | archive-url=https://web.archive.org/web/20180121201126/https://books.google.com/books?id=dVIWAAAAQBAJ&pg=PT1365 | archive-date=2018-01-21 }}</ref>

Growth from apical meristems is known as '''primary growth''', which encompasses all elongation.
'''Secondary growth''' encompasses all growth in diameter, a major component of [[woody plant]] tissues and many nonwoody plants. For example, storage roots of [[sweet potato]] have secondary growth but are not woody. Secondary growth occurs at the [[lateral meristem]]s, namely the [[vascular cambium]] and [[cork cambium]]. The former forms [[secondary xylem]] and [[secondary phloem]], while the latter forms the [[periderm]].

In plants with secondary growth, the vascular cambium, originating between the xylem and the phloem, forms a [[cylinder (geometry)|cylinder]] of tissue along the [[Plant stem|stem]] and root.{{citation needed|date=March 2016}} The vascular cambium forms new cells on both the inside and outside of the cambium cylinder, with those on the inside forming secondary xylem cells, and those on the outside forming secondary phloem cells. As secondary xylem accumulates, the "girth" (lateral dimensions) of the stem and root increases. As a result, tissues beyond the secondary phloem including the epidermis and cortex, in many cases tend to be pushed outward and are eventually "sloughed off" (shed).{{citation needed|date=March 2016}}

At this point, the cork cambium begins to form the periderm, consisting of protective [[cork (material)|cork]] cells. The walls of cork cells contains [[suberin]] thickenings, which is an extra cellular complex biopolymer.<ref>{{cite book |doi=10.1016/B978-0-7020-2933-2.00042-3 |chapter=Cell differentiation and ergastic cell contents |title=Trease and Evans' Pharmacognosy |date=2009 |last1=Evans |first1=William Charles |last2=Evans |first2=Daphne |pages=551–562 |isbn=978-0-7020-2933-2 }}</ref> The suberin thickenings functions by providing a physical barrier, protection against pathogens and by preventing water loss from the surrounding tissues. In addition, it also aids the process of wound healing in plants.<ref>{{Cite web|title=Suberin Form & Function – Mark Bernards – Western University|url=https://www.uwo.ca/biology/faculty/bernards/research/suberin_form__function.html|access-date=2021-08-31|website=www.uwo.ca}}</ref> It is also postulated that suberin could be a component of the apoplastic barrier (present at the outer cell layers of roots) which prevents toxic compounds from entering the root and reduces radial oxygen loss (ROL) from the [[aerenchyma]] during waterlogging.<ref name="ReferenceA">{{cite journal |last1=Watanabe |first1=Kohtaro |last2=Nishiuchi |first2=Shunsaku |last3=Kulichikhin |first3=Konstantin |last4=Nakazono |first4=Mikio |title=Does suberin accumulation in plant roots contribute to waterlogging tolerance? |journal=Frontiers in Plant Science |date=2013 |volume=4 |page=178 |doi=10.3389/fpls.2013.00178 |pmid=23785371 |pmc=3683634 |doi-access=free}}</ref> In roots, the cork cambium originates in the [[pericycle]], a component of the vascular cylinder.<ref name="ReferenceA"/>

The vascular cambium produces new layers of secondary xylem annually.{{citation needed|date=March 2016}} The xylem vessels are dead at maturity (in some) but are responsible for most water transport through the vascular tissue in stems and roots.
[[File:Tree branches and roots.jpg|thumb|Tree roots at Port Jackson|alt=]]
Tree roots usually grow to three times the diameter of the branch spread, only half of which lie underneath the trunk and canopy. The roots from one side of a tree usually supply nutrients to the foliage on the same side. Some families however, such as [[Sapindaceae]] (the [[maple]] family), show no correlation between root location and where the root supplies nutrients on the plant.<ref>{{cite journal |last1=van den Driessche |first1=R. |title=Prediction of mineral nutrient status of trees by foliar analysis |journal=The Botanical Review |date=July 1974 |volume=40 |issue=3 |pages=347–394 |doi=10.1007/BF02860066 |bibcode=1974BotRv..40..347V }}</ref>

===Regulation===
There is a correlation of roots using the process of [[plant perception (physiology)|plant perception]] to sense their physical environment to grow,<ref>{{cite journal | vauthors = Nakagawa Y, Katagiri T, Shinozaki K, Qi Z, Tatsumi H, Furuichi T, Kishigami A, Sokabe M, Kojima I, Sato S, Kato T, Tabata S, Iida K, Terashima A, Nakano M, Ikeda M, Yamanaka T, Iida H | display-authors = 6 | title = Arabidopsis plasma membrane protein crucial for Ca2+ influx and touch sensing in roots | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 104 | issue = 9 | pages = 3639–44 | date = February 2007 | pmid = 17360695 | pmc = 1802001 | doi = 10.1073/pnas.0607703104 | bibcode = 2007PNAS..104.3639N | doi-access = free }}</ref> including the sensing of light,<ref>{{cite press release |title=UV-B light sensing mechanism discovered in plant roots |url=https://phys.org/news/2008-12-uv-b-mechanism-roots.html |work=phys.org |publisher=San Francisco State University |date=8 December 2008 }}</ref> and physical barriers. Plants also sense gravity and respond through auxin pathways,<ref>{{cite journal | vauthors = Marchant A, Kargul J, May ST, Muller P, Delbarre A, Perrot-Rechenmann C, Bennett MJ | title = AUX1 regulates root gravitropism in Arabidopsis by facilitating auxin uptake within root apical tissues | journal = The EMBO Journal | volume = 18 | issue = 8 | pages = 2066–73 | date = April 1999 | pmid = 10205161 | doi = 10.1093/emboj/18.8.2066 | pmc = 1171291 }}</ref> resulting in [[gravitropism]]. Over time, roots can crack foundations, snap water lines, and lift sidewalks. Research has shown that roots have ability to recognize 'self' and 'non-self' roots in same soil environment.<ref>{{cite journal | vauthors = Hodge A | title = Root decisions | journal = Plant, Cell & Environment | volume = 32 | issue = 6 | pages = 628–40 | date = June 2009 | pmid = 18811732 | doi = 10.1111/j.1365-3040.2008.01891.x | doi-access = free | bibcode = 2009PCEnv..32..628H }}</ref>

The correct environment of [[Aeration|air]], mineral [[nutrients]] and [[water]] directs plant roots to grow in any direction to meet the plant's needs. Roots will shy or shrink away from dry<ref>{{cite journal|last1=Carminati|first1=Andrea|last2=Vetterlein|first2=Doris|last3=Weller|first3=Ulrich|last4=Vogel|first4=Hans-Jörg|last5=Oswald|first5=Sascha E. | name-list-style = vanc |title=When roots lose contact |journal=Vadose Zone Journal |date=2009 |volume=8|issue=3|pages=805–809|doi=10.2136/vzj2008.0147|bibcode=2009VZJ.....8..805C }}</ref> or other poor soil conditions.

[[Gravitropism]] directs roots to grow downward at [[germination]], the growth mechanism of plants that also causes the shoot to grow upward.<ref>{{cite journal | vauthors = Chen R, Rosen E, Masson PH | title = Gravitropism in higher plants | journal = Plant Physiology | volume = 120 | issue = 2 | pages = 343–50 | date = June 1999 | pmid = 11541950 | pmc = 1539215 | doi = 10.1104/pp.120.2.343 }}
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Different types of roots such as primary, seminal, lateral and crown are maintained at different gravitropic setpoint angles i.e. the direction in which they grow. Recent research show that root angle in cereal crops such as barley and wheat is regulated by a novel gene called Enhanced Gravitropism 1 (EGT1).<ref>{{cite journal |last1=Fusi |first1=Riccardo |last2=Rosignoli |first2=Serena |last3=Lou |first3=Haoyu |last4=Sangiorgi |first4=Giuseppe |last5=Bovina |first5=Riccardo |last6=Pattem |first6=Jacob K. |last7=Borkar |first7=Aditi N. |last8=Lombardi |first8=Marco |last9=Forestan |first9=Cristian |last10=Milner |first10=Sara G. |last11=Davis |first11=Jayne L. |last12=Lale |first12=Aneesh |last13=Kirschner |first13=Gwendolyn K. |last14=Swarup |first14=Ranjan |last15=Tassinari |first15=Alberto |last16=Pandey |first16=Bipin K. |last17=York |first17=Larry M. |last18=Atkinson |first18=Brian S. |last19=Sturrock |first19=Craig J. |last20=Mooney |first20=Sacha J. |last21=Hochholdinger |first21=Frank |last22=Tucker |first22=Matthew R. |last23=Himmelbach |first23=Axel |last24=Stein |first24=Nils |last25=Mascher |first25=Martin |last26=Nagel |first26=Kerstin A. |last27=De Gara |first27=Laura |last28=Simmonds |first28=James |last29=Uauy |first29=Cristobal |last30=Tuberosa |first30=Roberto |last31=Lynch |first31=Jonathan P. |last32=Yakubov |first32=Gleb E. |last33=Bennett |first33=Malcolm J. |last34=Bhosale |first34=Rahul |last35=Salvi |first35=Silvio |title=Root angle is controlled by EGT1 in cereal crops employing an antigravitropic mechanism |journal=Proceedings of the National Academy of Sciences |date=2 August 2022 |volume=119 |issue=31 |pages=e2201350119 |doi=10.1073/pnas.2201350119|doi-access=free |pmid=35881796 |pmc=9351459 |bibcode=2022PNAS..11901350F }}</ref>

Research indicates that plant roots growing in search of productive nutrition can sense and avoid soil compaction through diffusion of the gas [[ethylene]].<ref>{{cite journal |last1=Pandey |first1=Bipin K. |last2=Huang |first2=Guoqiang |last3=Bhosale |first3=Rahul |last4=Hartman |first4=Sjon |last5=Sturrock |first5=Craig J. |last6=Jose |first6=Lottie |last7=Martin |first7=Olivier C. |last8=Karady |first8=Michal |last9=Voesenek |first9=Laurentius A. C. J. |last10=Ljung |first10=Karin |last11=Lynch |first11=Jonathan P. |last12=Brown |first12=Kathleen M. |last13=Whalley |first13=William R. |last14=Mooney |first14=Sacha J. |last15=Zhang |first15=Dabing |last16=Bennett |first16=Malcolm J. |title=Plant roots sense soil compaction through restricted ethylene diffusion |journal=Science |date=15 January 2021 |volume=371 |issue=6526 |pages=276–280 |doi=10.1126/science.abf3013 |pmid=33446554 |bibcode=2021Sci...371..276P |hdl=1874/418726 |hdl-access=free }}</ref>
[[File:ArabidopsisLatRoot.jpg|thumb|Fluorescent imaging of an emerging lateral root]]