Plant Tissues

In biology, tissue is a cellular organizational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Broadly tissues can be classified into two major groups : Plant tissue and Animal tissue.

A plant tissue can be defined as a cell or a group of cells dividing, to give rise to large number of cell, which is collectively referred as tissues. They are structurally and functionally similar to these cells. Plants do have a higher level of structure called plant tissue systems. A plant tissue system can be defined as a functional unit, which connects all organs of a plant. Like animal tissue system, plant tissue system is also grouped into various tissues based on their functions.

In this lesson you will learn about :
1) Tissues - "The Teams of Workers"
2) Types of Plant Tissues
3) Plant Tissue Systems

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1. Plant Tissues

2. Tissues –“The Team of Workers”
Tissueisacellularorganizationallevelbetweencells
andacompleteorgan.
Atissueisanensembleofsimilarcellsand
theirextracellularmatrixfromthesameoriginthat
togethercarryoutaspecificfunction.
TheEnglishwordisderivedfromtheFrenchtissu,
meaningsomethingthatiswoven,fromtheverbtisser,
"toweave".
Thestudyofhumanandanimaltissuesisknown
as histology or, in connection with
disease,histopathology.
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The level of organization

3. BiswarupMajumder| Bio-World
Plant Tissue -Types
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4. MeristematicTissue / Meristem
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Meristematic(Gk.meristos=divisible)tissueisdefined
asamassofyoung,immatureandundifferentiatedcells,
whichremainyoungforeveranddividethroughoutthe
lifeoftheplant.
ClassificationofMeristems:
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(a) Based on position in the plant body

5. MeristematicTissue / Meristem
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(b)Basedontheoriginofformation
Meristematictissuefoundinadultplantandstill
activelydoescelldivision.
Location:Seenjustbelowpromeristem.
Function:Formstheprimarystructureoftheplant
body.
2. Primary meristems
3. Secondary meristems
Meristematictissuethatoriginatedfromprimary
permanenttissues[Someoftheprimarypermanent
tissuesregainmeristematicactivityandbecomes
secondarymeristem].
Location:Laterallyplacedinstemandroot.
Function:Responsibleforsecondarygrowthofthe
plant.
Example:Interfascicularcambiumandcorkcambiumof
stem,cambiumofroot.
1. Promeristems
Meristematictissuethathasexistedintheplantsince
theembryoniclevel.
Location:Extremetipofstemandroot.
Function:Formsprimarymeristemlatertheprimary
structureoftheplantbody.
We have a definite growth pattern and growth stops at certain
stage or age. But plant growth is indefinitedue to the presence of
meristems.

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Cellsaresmall.
Cellsareusuallycubical.
Cellwallisthin.
Nucleiarelarge.
Vacuolesalmostabsent.
Cellstightlypackedwithalmostnointercellularspaces.
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Characteristics:
A Typical MeristematicTissue
The cells actively divideadding new cells to the plant.
New cells thus produced are transformed into mature
permanent tissues.
Root Meristemof Onion
MeristematicCells

7. Permanent Tissue
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Thesetissuesarisefromthemeristematictissue.
Thecellsofthistissuegraduallyloosetheirpowerto
divideandacquireadefiniteshape,sizeandfunction.
Thesetissuesmaybelivingordead.
Thereare2typesofpermanenttissues:
1.Simplepermanenttissue
2.Complexpermanenttissue
Thistissuecomprisesofsametypeofcellswhichperform
thesamefunctionandallarisefromthesameorigin.
Thesearethreecategoriesofsimplepermanenttissues:
Parenchyma,Collenchyma,&Sclerenchyma.
SimplePermanentTissue:

8. Parenchyma
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Itisthefundamentaltissuecomposedofthinwalled,living
cellswhosecellwalliscomposedofcellulose.Smallintercellular
spacesarepresentbetweenthecells.
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Structure:
Itoccursinallsoftpartsofplantsandismeantforstorageof
foodandtoprovideturgiditytosofterpartsofplants.
Parenchymatissueinstemandrootsstorenutrientsandwater.
Location&Function:
Chlorenchyma-Certainparenchymatoustissuecontain
chloroplastandsynthesizefoodbytheprocessof
photosynthesis.
Aerenchyma-Inaquaticplantsparenchymatouscellshaveair
cavitiesbetweenthemtostoreair,suchatissueiscalled
Aerenchyma.Itprovidesbuoyancytotheaquaticplantssothat
theycanfloatinwater.
Types:

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Thistissueiscomposedofsomewhatelongatedcellswithcell
wallsthatareirregularlythickenedatcornersdueto
depositionofcelluloseorpectin.Theymaybeoval,circularor
polygonal.Verylittleintercellularspacesarepresent.
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Structure:
Itoccursbelowtheepidermisofstemandpetiole(stalkofthe
leaf)andaroundveins.
Location:
Thistissueprovidesmechanicalsupportandflexibilityandin
somecasesitmaypossesschloroplaststoperform
Photosynthesis.Thestemandleavesareabletobendeasily
andthencomebacktotheiroriginalpositionduetothe
presenceofcollenchyma.
Function:
Collenchyma

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Itisatissueofdeadandthickwalledcells,havingno
intercellularspaces.Thethickeningsareofcelluloseorlignin
orboth.Severalunlignifiedareascalledpitsoftendevelopon
walls.
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Structure:
Thistissueisusuallyfoundinthehardandstiffpartsofthe
plantlikeseedcoat,huskofcoconut,inthestemaround
vascularbundles,veinsofleavesandhardcoveringoffruits
andnuts.
Location:
Itisthechiefmechanicaltissueinplantsandisabletobear
push,pull,strainandshearingforces.Itprovidesstrengthto
plantpartsandalsoprotectsthedelicatepartsoftheplants.
Function:
They are of two types: fibresand sclereids.
Types:
Sclerenchyma

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Difference Between

12. Complex Permanent Tissue
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Atissuemadeupofmorethanonetypeofcells
functioningasaunitiscalledcomplextissue.
Therearetwotypesofcomplextissues-Xylemand
Phloem.
Theyarecalledvascularorconductingtissues.
Xylemhelpstotransportwaterandmineralsfromrootsto
allpartoftheplant.
Phloemhelpstotransportfood(sugar)fromleavestoall
otherpartsoftheplant.

13. Itisacomplexpermanenttissue,whichisspecialized
fortheconductionofwaterandmineralsubstancesin
theplantbody.
Xylemisaheterogenoustissuemadeupoffour
differenttypesofcellularelements.Theyare:
Ofthese,thetracheidsandthetracheaeare
describedasessentialelementssincetheyaredirectly
involvedinthetranslocationofwaterandmineral
substances.
Xylemfibersandxylemparenchymaaredescribedas
associatedelements,sincetheyareonlysupporting
structures.
Thetracheids,thetracheaandthexylemfibersare
non-livingcomponents,whilexylemparenchyma
representstheonlylivingcomponentofthetissue.
Xylem
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14. Xylem Components
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Thetracheidsareelongated,deadcells,withtaperingends.
Theyarecharacterisedbythepresenceofathickcellwall
consistingofprimarywallandasecondarywall.Theprimary
walliscomposedofcellulosewhereasthesecondarywallis
madeupoflignin.
Thereisaspaciouslumenthatextendsthroughoutthe
lengthofthetracheid.
Insomecases,duetothedepositionoflignin,theprimary
walldevelopsnumerousconcavedepressionscalledpits.
Whenpitsarepresent,thetracheidisdescribedaspitted
andwhenpitsareabsent,itisdescribedassimple.
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Xylem Tracheids:
Xylem Tracheae:
Theyarecommonlyknownasxylemvessels.
Thetracheaearefoundarrangedparalleltoeachother,
extendingfromoneendoftheplantbodytoanother.
Thetracheaearelongcylindricaldeadcells.
Theyarecharacterizedbyathickcellwallconsistingofa
primarywallandasecondarywall.Theprimarywallismade
upofcellulosewhereasthesecondarywallismadeupof
lignin.
Thereisaspaciouslumenthatextendsthroughoutthe
lengthofthetrachea.
Thedepositionoflignininthesecondarywallisnotalways
uniform.Asaresult,thexylemvesselsexhibitdifferent
typesofsecondarythickenings.

15. Xylem Components
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Theyarerepresentedbythedeadsclerenchymafibers
thatarefoundinbetweenthevesselsandthetracheids.
Theyaremeantforprovidingmechanicalsupporttothe
essentialelements.
XylemFibres:
Thisistheonlylivingcomponentinthexylemtissue.
Itisrepresentedbygroupsofparenchymacellsthatare
foundinbetweenthevesselsandthefibers.
Theyaremeantforstorageofreservefood.
XylemParenchyma:
The rings seen in the trunk of an old tree which has been cut
transversely are the xylem rings. The age of a tree can be
determinedby counting the number of rings.

16. Phloemisacomplexpermanenttissue,whichisspecialized
fortheconductionoffoodandotherorganicsubstances.
Phloemisalsoaheterogenoustissue,madeupoffour
differenttypesofcellularelements,namely,
Ofthese,thesievetubesandthecompanioncellsare
directlyinvolvedinthetranslocationoftheorganic
substances.Hence,theyarecommonlydescribedas
essentialelements.
Phloemparenchymaandphloemfibersaredescribedas
associatedelementssincetheyplayonlyasupportingrole
intheprocess.
Thesievetubes,thecompanioncellsandthephloem
parenchymarepresentthelivingcomponentsofthetissue
whilephloemfibresrepresenttheonlynonlivingcomponent
ofthetissue.
Phloemiscommonlydescribedasaliving,complex
permanenttissue.
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Phloem

17. Phloem Components
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Theyrepresentthemostactivefoodconductingelements
inthephloemtissue.
Thesievetubesarefoundarrangedparalleltooneanother
fromoneendoftheplantbodytoanother.
Eachsievetubeisformedbyaseriesofhollow,cylindrical
cellscalledsievetubecellsarrangedoneabovetheother.
Thesievecellsareseparatedfromeachotherby
horizontalperforatedplatescalledsieveplates.Thesieve
cellscommunicatewitheachotherthroughthesieveplates.
Eachsievecellhasathincellwall,whichiscomposedof
onlycellulose.Thecellhasacentralmassofdense
cytoplasm.Thegranularcytoplasmformsanumberof
projectionscalledcytoplasmicstrandsextendingtowards
thesieveplate.Thenucleusisabsent.
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Sieve Tubes:
Companion Cells:
Theyaremoreorlessspindleshapedcellsassociatedwith
thesievetubecells.
Eachcompanioncellisfoundattachedtoanyonelateral
surfaceofasievecell.
Thecompanioncellandtheneighboringsievecelltogether
representapairofsistercells.
Thecompanioncellhasagranularcytoplasm,prominent
nucleusandoneortwosmallvacuoles.Thenucleusofthe
companioncellissaidtobecapableofexertingits
influenceontheadjacentsievecells.

18. Phloem Components
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Phloemfibresarerepresentedbythedeadsclerenchyma
fibresthatarefoundinbetweenthesievetubes.
Theyaremeantonlyforprovidingmechanicalsupport.
PhloemFibres:
Phloemparenchymaisrepresentedbyagroupofliving
parenchymacellsthatarefoundin-betweenthesieve
tubes.
Theyaremeantonlyforstorageoforganicfood.
PhloemParenchyma:

19. Xylem vs. Phloem
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20. BiswarupMajumder| Bio-World 19
Plant Tissue System

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Plant Tissue System