《植物生物学》课程教学资源（文献资料）Characteristics of Monocotyledonous Roots_Botany

2020/2/13CharacteristicsofMonocotyledonousRootsBotanyNavigationCharacteristics ofMonocotyledonousRootsBotanyArticle Sharedby Harika GuptaADVERTISEMENTS:广告XVisualizecellswithout labelsHoloMonitor?creates software-generated imagesofyourcellswithout any stainingatall!Thefollowingpointshighlightthetopelevenanatomicalcharacteristics ofmonocotyledonousroots.The characteristics are: 1.Xylem 2. Cambium3.Pith4.Epidermis 5.Cortex 6.Endodermis 7.Pericycle 8.Vascular Tissue 9.Formation of LateralRoots1o.Mycorrhiza11.FormationofAdventitiousRoots.Monocotyledonous Roots:AnatomicalCharacteristics # 1.Xylem:The xylem groups are numerous (polyarch condition)andgenerally vary from twelve to twenty.www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botanyr206921/19

2020/2/13 Characteristics of Monocotyledonous Roots | Botany www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692 1/19 Navigation Characteristics of Monocotyledonous Roots | Botany Article Shared by ADVERTISEMENTS: The following points highlight the top eleven anatomical characteristics of monocotyledonous roots. The characteristics are: 1. Xylem 2. Cambium 3. Pith 4. Epidermis 5. Cortex 6. Endodermis 7. Pericycle 8. Vascular Tissue 9. Formation of Lateral Roots 10. Mycorrhiza 11. Formation of Adventitious Roots. Monocotyledonous Roots: Anatomical Characteristics # 1. Xylem: The xylem groups are numerous (polyarch condition) and generally vary from twelve to twenty. Visualize cells without labels HoloMonitor® creates software-generated images of your cells, without any staining at all!

2020/2/13Characteristics of Monocotyledonous RootsBotanyCORTEXXYLEMBIMACORTEXENDODERMISRICYCLEPHLOEMENTALJEDIFig.42.17.Theroot.Transectionthroughrootof Zeamays (monocot)showing a lateral root.Tnecortexand xylem are clearly visible in the lateral root.MonocotyledonousRoots:AnatomicalCharacteristics#2.Cambium:Thecambium isaltogether absenteven inlater stages,asthereisno secondarythickening in such roots.Monocotyledonous Roots:AnatomicalCharacteristics # 3.Pith:The pith is large and well developed. In certain cases (e.g., inCanna), the pith becomes sclerenchymatous.2/19www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692

2020/2/13 Characteristics of Monocotyledonous Roots | Botany www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692 2/19 Monocotyledonous Roots: Anatomical Characteristics # 2. Cambium: The cambium is altogether absent even in later stages, as there is no secondary thickening in such roots. Monocotyledonous Roots: Anatomical Characteristics # 3. Pith: The pith is large and well developed. In certain cases (e.g., in Canna), the pith becomes sclerenchymatous

2020/2/13CharacteristicsofMonocotyledonousRootsBotanyUSLAYERCORTEXENDODERMISSTELEUNICELLULARROOTHAIRLAYER(EPIBLEMACORTEXENDODPERICYCLEPASSAGECELLPROTOXYLEMMETAXYLENPHLOENPITHCORTEX:Fig.42.18.Root.T.S.ofmonocotyledonous root (iris),A, diagrammatic; B,detailedMonocotyledonousRoots:AnatomicalCharacteristics # 4.Epidermis:The epidermis or outermost layer of the root is commonlyknown as rhizodermis,epiblema orpiliferouslayer.Itisuniseriate and composed of compact tabular cells having nointercellular spaces and stomata.The tubular unicellularroot hairs arealsopresent on thislayer.Awellknownexampleofamultiseriateepidermisisthevelamenof aerial rootsof orchidsandepiphyticaroids(Guttenberg, 1940). The velamen is a parchment-like sheathconsistingofcompactlyarrangednon-livingcellswiththickened walls.The cells of velamen are quite big in sizeand containairandwaterinthem.Thecellwallsdevelopfibrousthickenings.Generallybeneath the epidermisthere are present one ormore layersofexodermis.Usuallytheexodermisconsistsofasinglerowwww.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/206923/19

2020/2/13 Characteristics of Monocotyledonous Roots | Botany www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692 3/19 Monocotyledonous Roots: Anatomical Characteristics # 4. Epidermis: The epidermis or outermost layer of the root is commonly known as rhizodermis, epiblema or piliferous layer. It is uniseriate and composed of compact tabular cells having no intercellular spaces and stomata. The tubular unicellular root hairs are also present on this layer. A well known example of a multiseriate epidermis is the velamen of aerial roots of orchids and epiphytic aroids (Guttenberg, 1940). The velamen is a parchment-like sheath consisting of compactly arranged non-living cells with thickened walls. The cells of velamen are quite big in size and contain air and water in them. The cell walls develop fibrous thickenings. Generally, beneath the epidermis there are present one or more layers of exodermis. Usually the exodermis consists of a single row

2020/2/13Characteristics of Monocotyledonous Roots Botanyof cells withthickened outer and lateral walls except certainpassagecells which remain thin-walled.EPIDERMISEXODERMISENDODERMISPERICYCLEPHLOEMMETAXYLEMPROTOXYLEMITHFig.42.19.Anatomyofroott.T.S.of.Smilaxroof(monocot)-detail of asectorMonocotyledonousRoots:AnatomicalCharacteristics # 5.Cortex:Immediatelybeneaththeepidermisamassivecortexliesconsisting of thin-walled parenchyma cells havingsufficientlydeveloped intercellular spaces amongthem.Usually in an old root of Zea may a few layers of corteximmediatelybeneaththeepidermisundergosuberizationandgiverisetoa simpleormulti-layered zone-theexodermis.Thisisprotectivelayerwhichprotectsinternaltissuesfrominjurious agencies!The starch grains are abundantlypresentinthecorticalcells.Thesclerenchymacellsarecommonlyfound inthe cortex ofmonocotyledons.JNICELLULARROOTHAIREPIDERMISCORTEXENDODERMISPERICYCLEPROTOXYLEMETAXYLEMPHLOEMASSAGECELLTHINWALLEDCELLSINENDODERMIS)Fig.42.20.Anatomyofmonocotroot.CrosssectionolrootofCommelina.www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botanyr206924/19

2020/2/13 Characteristics of Monocotyledonous Roots | Botany www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692 4/19 of cells with thickened outer and lateral walls except certain passage cells which remain thin-walled. Monocotyledonous Roots: Anatomical Characteristics # 5. Cortex: Immediately beneath the epidermis a massive cortex lies consisting of thin-walled parenchyma cells having sufficiently developed intercellular spaces among them. Usually in an old root of Zea may a few layers of cortex immediately beneath the epidermis undergo suberization and give rise to a simple or multi-layered zone—the exodermis. This is protective layer which protects internal tissues from injurious agencies! The starch grains are abundantly present in the cortical cells. The sclerenchyma cells are commonly found in the cortex of monocotyledons

2020/2/13Characteristics of Monocotyledonous Roots BotanyMonocotyledonousRoots:AnatomicalCharacteristics#6.Endodermis:TheinnermostlayerofthecortexiscalledtheendodermisIt is composed of barrel-shaped compact cells having nointercellular spaces among them. The endodermal cellspossess Casparian strips on their anticlinal walls. TheCasparianstripisthepart of primary cell wall.The stripistypicallylocated close tothe innertangential wall.Inmostofmonocotyledonstheendodermiscommonlyundergoescertainwallmodifications.Therearetwodevelopmental states, sometimes very distinct, in additiontotheprimarystatewhenonlytheCasparianstripispresent. In the secondary state a suberin lamella covers theentirewall ontheinsideofthecell.JNICELLULARROOTHAIREPIDERMISGENTHYMAYENDODERMISPERICYLEPHLOEMPROTOXYLEMMETAXYLEMTPARENCHYMAUNCTIVETISSUEFig.42.21.AnaAt a later stage of development this suberin lamella iscovered by a layer of cellulose which in some monocot rootsattains a considerablethickness.Thus the walls of theendodermalcellsbecomesufficientlythickenedandthethick-walled passage cells are formed opposite theprotoxylempoles.Thepassage cellsaremeantfordiffusionand are also called the transfusion cells.www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/206925/19

2020/2/13 Characteristics of Monocotyledonous Roots | Botany www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692 5/19 Monocotyledonous Roots: Anatomical Characteristics # 6. Endodermis: The innermost layer of the cortex is called the endodermis. It is composed of barrel-shaped compact cells having no intercellular spaces among them. The endodermal cells possess Casparian strips on their anticlinal walls. The Casparian strip is the part of primary cell wall. The strip is typically located close to the inner tangential wall. In most of monocotyledons the endodermis commonly undergoes certain wall modifications. There are two developmental states, sometimes very distinct, in addition to the primary state when only the Casparian strip is present. In the secondary state a suberin lamella covers the entire wall on the inside of the cell. At a later stage of development this suberin lamella is covered by a layer of cellulose which in some monocot roots attains a considerable thickness. Thus the walls of the endodermal cells become sufficiently thickened and the thick-walled passage cells are formed opposite the protoxylem poles. The passage cells are meant for diffusion and are also called the transfusion cells

2020/2/13CharacteristicsofMonocotyledonousRootsBotanyICELLULARROOTHAIRCUTICLEEPIDERMISCORTEX(PARENCHYMA)AIRSPACESENDODERMISERICYCLEPASSAGECELLPROTOXYLEMPHLOEMMETAXYLEMJUNCTIVETISSUEPITH(SCLERENCHYMA)Fig.42.22.Theroot.T.S.ofmonocotrootofOryza sativa (rice)showing air-spaces in cortexandsclerenchymatous pith.MonocotyledonousRoots:AnatomicalCharacteristics#7.Pericycle:It isusuallyuniseriate and composed ofthin-walledparenchymatous cells. In the monocotyledons, the pericycleoften undergoes sclerification in older roots,partlyorentirely. In many monocotyledons (e.g., some Gramineae,Smilax,Agave,Dracaena,palms)thepericycleconsists ofseveral layers.The pericycle may be interrupted by the differentiation ofxylem(manyGramineaeandCyperaceae)orphloemelements (Potamogetonaceae)nextto theendodermis(Guttenberg, 1943).Here, the pericycle gives rise to lateralroots only.www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/206926/19

2020/2/13 Characteristics of Monocotyledonous Roots | Botany www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692 6/19 Monocotyledonous Roots: Anatomical Characteristics # 7. Pericycle: It is usually uniseriate and composed of thin-walled parenchymatous cells. In the monocotyledons, the pericycle often undergoes sclerification in older roots, partly or entirely. In many monocotyledons (e.g., some Gramineae, Smilax, Agave, Dracaena, palms) the pericycle consists of several layers. The pericycle may be interrupted by the differentiation of xylem (many Gramineae and Cyperaceae) or phloem elements (Potamogetonaceae) next to the endodermis (Guttenberg, 1943). Here, the pericycle gives rise to lateral roots only

2020/2/13CharacteristicsofMonocotyledonousRootsBotanyNUCELHAASUTICLEEPIDERMISHYPODERMISCLEDENEHYMAPACRENTESMACHYENDODERMISPERICYCLEPACEAGEMETAXYLEMAETATIONEALPROTOXYLEM(SCLERENCHYMA)Fig.42.23.TherooLT.S.olmontAaeus pith anadditional metaxylem vessels.The cellsofcorticalregionarebeing arranged in distinctradialrowsCUTICLEEPIDERMSEXODERMISCORTEXASSAGECELINDODERMISRICYCLEPHLOEMROTOXYLEMMETAXYLEMCONJUNCTIVETISSUEFig.42.24.Theroot.T.S.ofmonocotyledonousroot(grass)MonocotyledonousRoots:AnatomicalCharacteristics#8.VascularTissue:Thevasculartissueconsists ofalternatingstrandsofxylemandphloem.Thephloemoccursintheformofstrandsneartheperipheryofthevascularcylinder,beneaththepericycle.Thexylemformsdiscretestrands,alternatingwiththephloem strands.The centre is occupied bylarge pith whichmaybeparenchymatous or sclerenchymatous.Bundles are numerous and referred as polyarch. TheadventitiousrootsofPalmaeandPandanaceaehaveconsiderably higher number of vascular bundles, as many as1oo or more. In some roots (e.g., Hydrilla, Triticum), asinglevessel occupiesthecentreandisseparatedbynon-tracheary elements from the peripheral strands. In otherwww.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/206927/19

2020/2/13 Characteristics of Monocotyledonous Roots | Botany www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692 7/19 Monocotyledonous Roots: Anatomical Characteristics # 8. Vascular Tissue: The vascular tissue consists of alternating strands of xylem and phloem. The phloem occurs in the form of strands near the periphery of the vascular cylinder, beneath the pericycle. The xylem forms discrete strands, alternating with the phloem strands. The centre is occupied by large pith which may be parenchymatous or sclerenchymatous. Bundles are numerous and referred as polyarch. The adventitious roots of Palmae and Pandanaceae have considerably higher number of vascular bundles, as many as 100 or more. In some roots (e.g., Hydrilla, Triticum), a single vessel occupies the centre and is separated by non￾tracheary elements from the peripheral strands. In other

2020/2/13Characteristics of Monocotyledonous Roots |Botanyvariablenumbersoflargemetaxylemvesselsarearrangedincircle around the pith (e.g., Zea mays)Inthe woodymonocotyledonstheinnermetaxylemelementsmayform two tothree circles (e.g., Latana),orthey may be widely separated from each other (e.g.,Phoenixdactylifera), or scattered throughout the centre (e.g., Raphiahookeri).In some monocotyledons (e.g., Cordyline, Musa,Pandanaceae) phloem strands are scattered among thetrachearyelements inthe centreofthe root.ADVERTISEMENTS:The xylem is exarch, ie., the protoxylem lies towardsperiphery and themetaxylem towards the centre.Thevesselsofprotoxylemarenarrowandthewallshaveannularandspiralthickeningswhereasthatofmetaxylemthevessels are broad and they possess reticulate and pittedthickenings.Thephloem strandsconsist ofsievetubes,companion cellsandphloemparenchyma.Thephloemstrandsarealsoexarch having protophloem towards the periphery andmetapholem towards the centre.The parenchymatous orsclerenchymatousconjunctivetissueisfoundinbetweenand around the xylem and phloem strands.The central part of the stele is occupied by a well developedpith.In Canna, Oryza sativa, Avena sativa,the pith issclerenchymatous.PARENKTLENFig.42.25.T.S.otmoonocot rootot Hydrilla showinglargeairspacesincortexandsinglexylemcavityMonocotyledonousRoots:AnatomicalCharacteristics # 9.8/19www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692

2020/2/13 Characteristics of Monocotyledonous Roots | Botany www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692 8/19 variable numbers of large metaxylem vessels are arranged in circle around the pith (e.g., Zea mays). In the woody monocotyledons the inner metaxylem elements may form two to three circles (e.g., Latana), or they may be widely separated from each other (e.g., Phoenix dactylifera), or scattered throughout the centre (e.g., Raphia hookeri). In some monocotyledons (e.g., Cordyline, Musa, Pandanaceae) phloem strands are scattered among the tracheary elements in the centre of the root. ADVERTISEMENTS: The xylem is exarch, i.e., the protoxylem lies towards periphery and the metaxylem towards the centre. The vessels of protoxylem are narrow and the walls have annular and spiral thickenings whereas that of metaxylem the vessels are broad and they possess reticulate and pitted thickenings. The phloem strands consist of sieve tubes, companion cells and phloem parenchyma. The phloem strands are also exarch having protophloem towards the periphery and metapholem towards the centre. The parenchymatous or sclerenchymatous conjunctive tissue is found in between and around the xylem and phloem strands. The central part of the stele is occupied by a well developed pith. In Canna, Oryza sativa, Avena sativa, the pith is sclerenchymatous. Monocotyledonous Roots: Anatomical Characteristics # 9

2020/2/13Characteristics of Monocotyledonous Roots BotanyFormation of Lateral Roots:Infloweringplants,thelateral roots areendogenous inorigin,that is, theyoriginate in the inner tissue ofthemother root,and appearexternallyonlyafter theirgrowth iswell begun.The root meristems arise in the pericycle foundimmediatelybeneaththeendodermis.(Inferns,andotherpteridophytes thelateral roots originate in theendodermis).Usuallythe lateral roots arerestrictedto the regionsoppositethexylemand comeout in vertical rows,thenumber being equal to that of xylem strands present.In theformation of a lateral root, the cells ofthepericycle lyingagainsttheprotoxylembecomemeristematicandbegintodivide first tangentially and then periclinally andanticlinally,thus a few layers of cells are cut offThis way,the endodermis is pushed outwards and aprotrusion is being formed. Very soon this protrusion comesout of the cortex and three regions of root apex, that is,dermatogen,periblem and plerome,becomequitedistinct.Theendodermisand someofthecorticalcellsformapartoftheroot cap.Thelateral rootforces its wayout through thecortex,endodermisandepidermis,andpassesintothesoilVery soon the root cap is sloughed off and renewed by thecalyptrogen.ELLULARROOTHAIRUTICLEPCELLULARCORTEHYMAENDODERMISMETAXYLEMPERICYCLEPROTOXYLEMTESSLEMFig..42.26.Thenwww.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/206929/19

2020/2/13 Characteristics of Monocotyledonous Roots | Botany www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692 9/19 Formation of Lateral Roots: In flowering plants, the lateral roots are endogenous in origin, that is, they originate in the inner tissue of the mother root, and appear externally only after their growth is well begun. The root meristems arise in the pericycle found immediately beneath the endodermis. (In ferns, and other pteridophytes the lateral roots originate in the endodermis). Usually the lateral roots are restricted to the regions opposite the xylem and come out in vertical rows, the number being equal to that of xylem strands present. In the formation of a lateral root, the cells of the pericycle lying against the protoxylem become meristematic and begin to divide first tangentially and then periclinally and anticlinally, thus a few layers of cells are cut off. This way, the endodermis is pushed outwards and a protrusion is being formed. Very soon this protrusion comes out of the cortex and three regions of root apex, that is, dermatogen, periblem and plerome, become quite distinct. The endodermis and some of the cortical cells form a part of the root cap. The lateral root forces its way out through the cortex, endodermis and epidermis, and passes into the soil. Very soon the root cap is sloughed off and renewed by the calyptrogen

2020/2/13CharacteristicsofMonocotyledonousRoots|BotanyUNICELLULARROOTHAIECITCLEPIDERMSEXODERMISORTE(PARENCHYMA)ENDODERMISPASSAGE CELLPERICYCLEPROTOXYLEMMETAXYLEMPHLOEMCTIVEISSUEFig, 42.27. The root. T.S. of monous root (Alium cepa),ovaoMETAXYLEMENATERALROOTDFig.42.28,Arrangement of primaryvasculartissues and the orientation of lateral root with referencetovasculartissues ofthemainroot.A-D,diarchtotetrarch (in dicot):E,polyarch (in monocot)LateralrootarisesoppositethephloempolesinAandEoppositetheprotoxylempolesinCandDbetweenxylemandphloempolesinB.Fig,42.29.Position of origin of tatetat roots; AE.various position.rays:F,position(oppositexylemrays)foundirangiosperms whereroothas less than threexylemroots of allvascularplantswheretherearethreeormorexylem tays.Thelateralrootprimodriaareformedindistinctivepositions in relation to the xylem and phloem of the parentroot.Indiarchrootstheyusuallyoccurbetweenthexylemandthephloem,intriarchandtetrarchrootsinpositionswww.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/2069210/19

2020/2/13 Characteristics of Monocotyledonous Roots | Botany www.biologydiscussion.com/root/characteristics-of-monocotyledonous-roots-botany/20692 10/19 The lateral root primodria are formed in distinctive positions in relation to the xylem and phloem of the parent root. In diarch roots they usually occur between the xylem and the phloem, in triarch and tetrarch roots in positions