Vegetative Morphology of Plant's Root- A Comprehensive Study.

This presentation consists of a comprehensive study of the morphology of the plant's root with the degree of modifications they experienced to address the emerging needs in the context of stress and other issues. It also offers the bird's eye view of the structural and functional issues of the root as the important organ for plant survival.

1. ROOT-A COMPREHENSIVE
STUDY
Presented by
Dr. N. Sannigrahi,
Associate Professor,
Department of Botany,
Nistarini College, Purulia,
D.B. Road, Purulia (W.B),
India-723101

2. Rootasdescendingpartistheextensionandmodificationoftheradicalof
thegerminatingseedsofthehigherplants.
Rootshavenonodesorinternodespatternofconstruction,
Noleaves,nobranchingfromregularspots,novegetativebudmostly,
Growsdownwardandholdstheplantstightlytoabsorbwater,minerals
alongwithstorageandothersecondaryfunctions,
Mostlycylindricalinstructure,
Positivelygeotropicandhydrotropicbutnegativelyphototropic,
Mostlycolorless,whitewithoutchlorophyll,
Rootcappresentovertheapexoftheroot,
Sixtypesofroots-taproots,fibrousroot,lateralroots,adventitiousroot,
storagerootsandaerial;roots,
Alotofspecialtiesaccordingtoneedbymodifications,
Plantswithoutroot:Wolfiaarrhiza,Utriculariastellaris

4. Tap root consists of the following parts;
RootCapregion-Therootcapprotectsthegrowingtipinplants.Itsecretes
mucilagetoeasethemovementoftherootthroughsoil,andmayalsobe
involvedincommunicationwiththesoilmicrobiota.Thepurposeofthe
rootcapistoenabledownwardgrowthoftheroot,withtherootcap
coveringthesensitivetissueintheroot.itmaybemultiplerootcaplike
Pandanusodoratissumus.ItmaycontainrootpocketlikeEichornia,
Pistia,Lemnaetc.
MeristematicZone-Justabovetherootcap,meristematiclayerscomprising
ofdelicatecellwall,densecytoplasmandenlargednucleuscontaining
zone.
ZoneofElongation-Alayerofextendedpart,
RootHairRegion-Consistsofnumerous,unicellularhairs,
PermanentRegion-Justabovethezoneofabsorption,anextendedlayer
comprisingofpermanenttissuespresent.

6. HigherPlantsmainlyangiospermbroadlydividesintotwocategories-
monocotanddicotandtheydiffertoeachotheronthebasisofinternal
structuresingeneralandthenumberofvascularbundlesinparticular.
Thecommonfeaturesareasfollows:
Nocuticleintheepidermis,
Epidermis-outersinglelayeredparenchymacellswithunicellularhairs,
GeneralCortex-Mostlyaseriesofparenchymatoustissueswithno
intercellularspacestostorestarchandorganicmatterasreservefood
matters,
Endodermis–theinnermostlayer,acompactareaofcellsencircledby
fattybandinsideeachcelltoestablishvascularconnection,
Pericycle-alayerofcellsencirclesthevascularcylinder,
Thevascularbundles-madeupofxylemandphloeminradialfashion,up
to4-6indicotrootandmorethan6inmonocotroot,exarchxylem,
Nopithpresent,
Somemodificationslikepassagecellspresentintheendodermis.

8. Beside the normal function of root like mechanical function, physiological
function and some special function, it undergoes a series of change to
respond stress as a part to resume normal function. The following type of
modifications are found :
MODIFICATION OF TAP ROOT
Storage root-To store food, some roots undergo swollen and enlarged , the
root branches become fibrillar in nature.
A. Fusiform -Middle part swells and the two ends taper as found in radish,
Raphanus sativus ( Brassicaceae).
B. Conical-The upper part swells and gradually narrower in the lower part
giving conical shape as found in carrot, Daucas carota (Brassicaceae),
C. Napiform -The upper part swells but the lower portion immediately
narrower like tail like structure as found in Brassica napus ( Brassicaceae).
D. Tuberous-The tap root swells but do not undergo any special shape as
found in four o’ clock plant, Mirabilis jalapa (Nyctaginaceae)

10. MODIFICATIONOFBRANCHROOT
Thebranchrootundergoesthefollowingtypesofmodifications.
A.Nodulatedroot-Therootsoflegumesdevelopthenoduledueto
biochemicalmodificationstorefugethenitrogenfixingbacteriaasapartof
theatmosphericnitrogenintosolublenitratefortheuptakebytheplantsas
foundinalmostallthemembersofFabaceaelikePisumsativum.
Pneumatophores–Normally,therootstakesoilairasoxidizingsourceof
respirationbutinhalophytes,tocompensatemoreoxygendemand,the
rootsbecomenegativelygeotropicanddevelopmodifiedrootstructures
calledpneumatophoresandtheporesarecalledpneumatothodesasfound
inHeritierafomes(SterculiodeaeofMalvaceae)),Ceriopsroxburghiana
(Rhizophoraceae).
MODIFICATIONSOFADVENTITIOUSROOT
Storageroots
Tuberousroot-Thenodesofthecreepersdevelopsuchtypeofrootsfor
storageasfoundinsweetpotato,Ipomoeabatatus(Convolvulaceae)

12. Fasiculatedroot–Fromthelowermostnodeofthestem,thefibrousroots
appearandundergoswellingduetofoodstorageasfoundinAsparagus
racemosus(Asparagaceae)andDahliahybrida(Asteraceae).
Nodulatedroot-Theterminalportionoftheadventitiousrootswellsdueto
foodstorageasfoundinCurcumaamada(Zingiberaceae)andCannaindica
(Cannaceae).
MoniliformorBeadedroot-Theadventitiousrootsundergoesswellingand
normalataregularintervalsandappearasbeadsasfoundinMormordica
cochinchinensis(Cucurbitaceae)andMormordicacharantia(
Cucurbitaceae).
Annulatedroot-Theadventitiousrootsgraduallyappearasballorannular
growthsasfoundinIpecac,Psychotriaipecacuanha(Rubiaceae).
ADVENTITIOUSROOTSMODIFICATIONSFORPHYSIOLOGICAL
MODIFICATIONS:
Epiphyticroot-Thesearerootsofsomeparasitesthatfloatsonair;have
velamenlikespongetissuestoabsorbatmosphericwaterasVanda
roxburghii(Orchidaceae)

14. AssimilatoryRoot-Somerootsderivefromtheinternodesofstem,
conductphotosynthesisduetochlorophyllasfoundinTinosporacordifolia
(Menispermaceae)andTrapabispinosa(Lathraceae).
ParasiticRootorHaustoria–Somerootsderivedfromthenodesofsome
parasites,invadethephloemofthehostplantfornutritionasfoundin
Cuscutareflexa(Convolvulaceae).
FloatingRoot–Inaquaticplants,theadventitiousrootdevelopfromnodes
thatenablestofloatandundergorespirationasfoundinJussiaearepens(
Onagraceae)nowknownasLudwigiaadscendens.
ReproductiveRoot-Veryoftentheadventitiousrootdevelopthe
reproductivebudtoformnewindividualasfoundinTrichosanthesdioica(
Cucurbitaceae),Ipoeabatatus(Convolvulaceae).
Thus,thesearetypeofmodificationsfordifferentphysiologicalfunctions
asextendedbyplantsofdiversegroups.

16. PropRoot-Theadventitiousrootsdevelopfromtheexpandedportionof
thestem,hangonthelowersidewithrootcaponthetipandappearasprop
towithstandthepressureexertedfromthetrunk.Veryoften,itextendthe
functioninabsenceoftaprootasfoundinFicusbenghalensis(Moraceae).
StiltRoot-Fromthelowerpartofthestem,somenodesdevelop
adventitiousrootandverticallypushedintothesoilknownasstiltrootto
standerectandextendphysiologicalfunctionsfoundinPandanus
fascicularis(Pandanaceae),Zeamays(Poaceae)etc.
RootButtress–Thesearetheaerialextensionsofthelateralsurfaceroots
havingtheinternalorganizationoftheadmixtureofrootandstemasfound
inBombyxceiba(Bombaceae).Ithelpstowithstandpressureexertedby
theheavycrownofthestandingplant.
ClimbingRoot-Climbingrootsaretheadventitiousrootsthatarisefrom
thenodesorinternodesinplantshavingweakstems.Theserootshelpthe
plantsinclimbingbypenetratingthecracksofthesupport,asinPothos
(moneyplant)ortheymaystickfirmlytoasupportbysecretinga
cementinggummysubstance,asinFicuspumila(Moraceae)

18. ContractileRoot-Contractilerootsareresponsibleformovementofthe
undergroundshootpartoftheplant,e.g.,acorm,abulb,ora.rhizome.
Movementofsuchorgansmustovercomesoilresistance,andthusit
dependsonseveralsoilparameters,e.g.,soil.type,moisture,and
mechanicalstability.Theexpansionandcontractionofthecontractileroot
enablestheplanttoresumeitsnormalpositionasfoundinCannaindica
(Cannaceae),Aliumcepa(Liliaceae)etc.
ThornRoot-Rootthornsarestronglysclerenchymatizedrootsarisingon
thestemabovetheground.Itsavestheplantagainstherbivores.Thesharp
thornsmayalsosavepropertieswhengrownasahedge.Theseroots
mainlyconferprotectiontotheplantsfromthedifferentadversesituations
asfoundinthemembersofArecaceaelikeBorassusflebllifer.
Haptera-Inadditiontothese,someplantsofhillyregionsdevelopsome
specialrootsgetattachedtotherocksurfacecalledHapteraasfoundin
Podostemumsp.

20. Theclassicaltaxonomyofplantneedsthemorphologyoftherootforthe
identificationoftheplantinordertogetanholisticideaofthestudy
material.Herearesomeoftheinformationthatcanbeusedinthisregard.
Theidentificationoftaxabytheirrootwouldallowspeciesspecific
questiontoaddress,
Taprootandfibrousrootscanhelptomakedifferencebetweenmonocot
anddicotplants,
Thedifferenttypeofundergroundmodificationsenabletoidentifyspecies
inthehierarchicallevel,
Preparationofkeycanbedoneonthebasisofrootcharacters,
Althoughrootistheundergroundpart,itdevelopsthechallengesasfaras
theidentificationofplantsonthebasisofthischaracter.

21. References:
Google for different images incorporated into this PPT,
Different WebPages for reference and content,
Disclaimer:
Thispresentationhasbeenmadeanddesignedasthefreeopensourceof
studymaterialsintendedfortheacademicfraternity.Thepresenterdoesnot
claimanykindoffinancialinterestforthiswork.Itiscompletelyfreefor
use.