Root: Difference between revisions

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Root morphology is divided into four zones: the root cap, the [[apical meristem]], the elongation zone, and the hair.<ref name="Okon1993">{{cite book|author=Yaacov Okon|title=Azospirillum/Plant Associations|url=https://books.google.com/books?id=I07BKGI8rboC&pg=PA77|date=24 November 1993|publisher=CRC Press|isbn=978-0-8493-4925-6|pages=77–}}</ref> The [[root cap]] of new roots helps the root penetrate the soil. These root caps are sloughed off as the root goes deeper creating a slimy surface that provides lubrication. The apical meristem behind the root cap produces new root cells that elongate. Then, root hairs form that absorb water and mineral nutrients from the soil.<ref name=arizona>{{cite web |title=Backyard Gardener: Understanding Plant Roots |website=University of Arizona Cooperative Extension |url=https://cals.arizona.edu/yavapai/anr/hort/byg/archive/understandingplantroots.html}}</ref> The first root in seed producing plants is the [[radicle]], which expands from the plant embryo after seed germination.

When dissected, the arrangement of the cells in a root is [[root hair]], [[Epidermis (botany)|epidermis]], [[epiblem]], [[Cortex (botany)|cortex]], [[endodermis]], [[pericycle]] and, lastly, the [[vascular tissue]] in the centre of a root to transport the water absorbed by the root to other places of the plant.~~{{clarify|reason=need diagram |date=March 2016}}~~

When dissected, the arrangement of the cells in a root is [[root hair]], [[Epidermis (botany)|epidermis]], [[epiblem]], [[Cortex (botany)|cortex]], [[endodermis]], [[pericycle]] and, lastly, the [[vascular tissue]] in the centre of a root to transport the water absorbed by the root to other places of the plant.

[[File:Ranunculus Root Cross Section.png|thumb|Ranunculus Root Cross Section]]

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'''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}}~~

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. 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).

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 web|title=Suberin – an overview {{!}} ScienceDirect Topics|url=https://www.sciencedirect.com/topics/medicine-and-dentistry/suberin|access-date=2021-08-31|website=www.sciencedirect.com}}</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|date=2013|title=Does suberin accumulation in plant roots contribute to waterlogging tolerance?|journal=Frontiers in Plant Science|volume=4|page=178|language=English|doi=10.3389/fpls.2013.00178|pmid=23785371|issn=1664-462X|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.

The vascular cambium produces new layers of secondary xylem annually. 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|last=van den Driessche|first=R.|date=1974-07-01|title=Prediction of mineral nutrient status of trees by foliar analysis|url=https://doi.org/10.1007/BF02860066|journal=The Botanical Review|language=en|volume=40|issue=3|pages=347–394|doi=10.1007/BF02860066|s2cid=29919924|issn=1874-9372|via=Springer}}</ref>

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[[File:Visible roots.jpg|thumb|Visible roots]]

The roots, or parts of roots, of many plant species have become specialized to serve adaptive purposes besides the two primary functions~~{{clarify|reason=there's no intro section|date=March 2016}}~~, described in the introduction.

The roots, or parts of roots, of many plant species have become specialized to serve adaptive purposes besides the two primary functions, described in the introduction.

* '''Adventitious roots''' arise out-of-sequence from the more usual root formation of branches of a primary root, and instead originate from the stem, branches, leaves, or old woody roots. They commonly occur in [[monocot]]s and pteridophytes, but also in many [[dicot]]s, such as [[clover]] (''Trifolium''), [[ivy]] (''Hedera''), [[strawberry]] (''Fragaria'') and [[willow]] (''Salix''). Most aerial roots and stilt roots are adventitious. In some conifers adventitious roots can form the largest part of the root system.

* '''Aerating roots''' (or '''knee root''' or '''knee''' or '''pneumatophores'''): roots rising above the ground, especially above water such as in some [[mangrove]] genera (''[[Avicennia]], [[Sonneratia]]''). In some plants like ''Avicennia'' the erect roots have a large number of breathing pores for exchange of gases.

@@ Line 13: / Line 13: @@
 Root morphology is divided into four zones: the root cap, the [[apical meristem]], the elongation zone, and the hair.<ref name="Okon1993">{{cite book|author=Yaacov Okon|title=Azospirillum/Plant Associations|url=https://books.google.com/books?id=I07BKGI8rboC&pg=PA77|date=24 November 1993|publisher=CRC Press|isbn=978-0-8493-4925-6|pages=77–}}</ref> The [[root cap]] of new roots helps the root penetrate the soil. These root caps are sloughed off as the root goes deeper creating a slimy surface that provides lubrication. The apical meristem behind the root cap produces new root cells that elongate. Then, root hairs form that absorb water and mineral nutrients from the soil.<ref name=arizona>{{cite web |title=Backyard Gardener: Understanding Plant Roots |website=University of Arizona Cooperative Extension |url=https://cals.arizona.edu/yavapai/anr/hort/byg/archive/understandingplantroots.html}}</ref> The first root in seed producing plants is the [[radicle]], which expands from the plant embryo after seed germination.
-When dissected, the arrangement of the cells in a root is [[root hair]], [[Epidermis (botany)|epidermis]], [[epiblem]], [[Cortex (botany)|cortex]], [[endodermis]], [[pericycle]] and, lastly, the [[vascular tissue]] in the centre of a root to transport the water absorbed by the root to other places of the plant.{{clarify|reason=need diagram |date=March 2016}}
+When dissected, the arrangement of the cells in a root is [[root hair]], [[Epidermis (botany)|epidermis]], [[epiblem]], [[Cortex (botany)|cortex]], [[endodermis]], [[pericycle]] and, lastly, the [[vascular tissue]] in the centre of a root to transport the water absorbed by the root to other places of the plant.
 [[File:Ranunculus Root Cross Section.png|thumb|Ranunculus Root Cross Section]]
@@ Line 67: / Line 67: @@
 '''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}}
+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. 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).
 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 web|title=Suberin – an overview {{!}} ScienceDirect Topics|url=https://www.sciencedirect.com/topics/medicine-and-dentistry/suberin|access-date=2021-08-31|website=www.sciencedirect.com}}</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|date=2013|title=Does suberin accumulation in plant roots contribute to waterlogging tolerance?|journal=Frontiers in Plant Science|volume=4|page=178|language=English|doi=10.3389/fpls.2013.00178|pmid=23785371|issn=1664-462X|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.
+The vascular cambium produces new layers of secondary xylem annually. 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|last=van den Driessche|first=R.|date=1974-07-01|title=Prediction of mineral nutrient status of trees by foliar analysis|url=https://doi.org/10.1007/BF02860066|journal=The Botanical Review|language=en|volume=40|issue=3|pages=347–394|doi=10.1007/BF02860066|s2cid=29919924|issn=1874-9372|via=Springer}}</ref>
@@ Line 107: / Line 107: @@
 [[File:Visible roots.jpg|thumb|Visible roots]]
-The roots, or parts of roots, of many plant species have become specialized to serve adaptive purposes besides the two primary functions{{clarify|reason=there's no intro section|date=March 2016}},  described in the introduction.
+The roots, or parts of roots, of many plant species have become specialized to serve adaptive purposes besides the two primary functions,  described in the introduction.
 * '''Adventitious roots''' arise out-of-sequence from the more usual root formation of branches of a primary root, and instead originate from the stem, branches, leaves, or old woody roots. They commonly occur in [[monocot]]s and pteridophytes, but also in many [[dicot]]s, such as [[clover]] (''Trifolium''), [[ivy]] (''Hedera''), [[strawberry]] (''Fragaria'') and [[willow]] (''Salix''). Most aerial roots and stilt roots are adventitious. In some conifers adventitious roots can form the largest part of the root system.
 * '''Aerating roots''' (or '''knee root''' or '''knee''' or '''pneumatophores'''): roots rising above the ground, especially above water such as in some [[mangrove]] genera (''[[Avicennia]], [[Sonneratia]]''). In some plants like ''Avicennia'' the erect roots have a large number of breathing pores for exchange of gases.