Fungi- Cell Wall & Thallus Structure.pdf

This Presentation has been made to explore the cell wall and range of thallus structure & its modification for academic pleasure.

1. MYCOLOGY
PRESENTATION BY:
Dr.N.Sannigrahi,
AssociateProfessor,
DepartmentofBotany,
NistariniCollege,Purulia,
D.B.Road,Purulia
(W.B),723101,
INDIA.

2. CONTENTS
Fungi as cell,
Cell components,
Thallus organization,
Thallus modifications,
Special structure of thallus,
Cell wall-Structure & Function,
Ultra structure of cell wall & Composition,
Conclusions.

3. FUNGAL CELL
Fungiasubiquitousintheformofsaprophytes,parasitesorsymbionts
istheeukaryoticinnaturewithwidediversityasfarasthesomatic
structureisconcerned.Thefungienjoysawiderangeasfaras
reproductionisconcernedandthecellularorganizationalbeautyhas
madeituniqueoneinthisrespect.
Eukaryoticwithdistinctcellwall.Cytoplasm&nucleus,
Uninucleateormultinucleateascoenocytes,
Heterokaryoticorhomokarioticinnature,
Nucleuscontainsoneormorenucleoli,
Cytoplasmcolorlessandgranulartoreticulateinappearance,
Cytoplasmcontainsmanybigbutirregularvacuoleswhereasthe
highermemberscontainsinglelargevacuolefoundincentralposition,
Cellscontainmitochondriaandcomplexsystemofinternalmembranes
includingER,Golgiapparatus,
Cellmembranecontainergosterolthatreplacethecholesterolinanimal
cells.

4. TYPICAL FUNGAL CELL

5. THALLUS ORGANISATION
UnicellularThallus:
Insomeofthelowerfungisuchasthechytrids,thethallusismoreorlessa
spherical,single-celledstructure.Atthetimeofreproduction,itbecomesa
reproductiveunit.Thelatterproducestheasexualorsexualcells.Suchfungi
arecalledholocarpic.Inthem,thevegetativeandreproductivestagesdonot
occurtogetherinthesamethallus.
Plasmodiophorahasavegetativephaseconsistingofanaked,multi-
nucleate,amoeboidmassofprotoplasm.ItistermedPlasmodium.The
protoplastofthediploidPlasmodiumcleavestoformtherestingspores.The
yeasts,whicharerelatedtothefilamentousforms,alsohaveaunicellular
thallus.Intheunicellularholocarpicforms(Synchytrium)themyceliumis
absent.
Filamentous Thallus :
Thevastmajorityofthefungihaveafilamentousthallus.Itoriginates
throughthegerminationofaspore.Thesporegerminatesasitlandsona
suitablesubstratumwhereotherconditionsoflifearealsofavorable.In
somespecies,thespore,ongermination,producesonlyashort,tubular
structureoflimitedgrowth.

6. RANGE OF THALLUS STRUCTURE

7. RANGE OF THALLUS STRUCTURE
Itconstitutesthethallusandistechnicallycalledahypha.Thesporesof
mostofthefungi,however,giverisetoafluffythallusconsistingofa
cottonymassoffine,branchedfilaments.Theselong,finefilamentsare
calledthehyphae(sing,hypha).Someofthesehyphae,atacertainstageof
maturity,extendintotheairandbearthereproductivebodies.
Therestspreadoverorwithinthesubstratumandcontinuethenormal
activities.Suchfungiarecalledeucarpic.Collectivelythehyphaecomprise
thevegetativebody(thallus)ofafunguswhichiscalledthemycelium.The
hyphaisthusastructuralunitofthemycelium.Itconsistsofathin,
transparentwallfilledorlinedwithalayerofcytoplasm.
Themediumuponwhichthemyceliumgrowsisknownassubstratum.The
myceliumisthefoodprocuringstructureinthelifecycle.Itcarriesonthe
generalactivitiesofaplantcellsuchasabsorption,digestion,respiration,
excretionandgrowthbutnotphotosynthesis.Thehyphaeconstitutingthe
myceliumbranch,spreadinalldirectionswithinoroverthesubstratumto
formalooseandramifyingnetwork.

8. RANGE OF THALLUS STRUCTURE
Thehyphaeareusuallycolourlessparticularlythoseembeddedinthe
substratum.Theaerialhyphaeinsomefungibecomecolored.Black,
orange,yellow,red,blueandbrownaretheusualtints.Thecolorisusually
confinedtothehyphalwall.
Evenwhenthepigmentsarepresentintheprotoplasmiccontents,theydo
notformanintegralpartofthelivingmatter.Thepigmentsplaynorolein
thephysiologyofthefungus.Thegrowthinlengthtakesplaceatthetipsof
thehyphaeandisthustermedapical.
Thethallusmaybegroupedinto-holocarpicoreucarpic;Whenthethallusasa
wholeisvegetativeaswellasreproductiveinfunction-holocarpicbutwhenthe
portionofthehyphaeofthethallustakespartinreproduction-eucarpic.
Hyphae-aerialorsubstrate,botharebranched;substratehyphaefornutrientsbut
aerialhyphaeforreproductivestructures,lookblack,red,blue,green,brownin
colordiversity;
Hyphaemaybemodified-Prosenchyma,Pseudoparenchyma,Rhizomorph,
Sclerotia,Sporophore,Stromaetcdependingonspeciesdiversity.

9. KINDS OF MYCELIUM
Thefungusmyceliuminfact,isamultinucleatestructurelacking
completeinternalcellboundaries.
i.AseptateMycelium-Inalgalfungi,itismultinucleate,aseptate,
growsterminallybytheapicalelongationofthehyphaeaccompanied
byincreaseinthenumberofnucleibynucleardivision,becomes
coenocytes.
Ii.SeptateMycelium-Developinternalcrosswallsthatdividethe
hyphaeintosegmentsatregularintervalsbehindthehyphaltip,
segmentsuninucleateormultinucleate.Formationofseptaisalways
precededbythedivisionofnucleus,eachhasacentralporeorrarely
morethanoneporealthoughcompletepartitionsdonotoccurduring
vegetativephase.
MostlyfoundinthemembersofAscomycetes&Basidiomycetes,
InBasidiomycets,furtherelaborationoftheseptumtoproduceamore
complexporecalleddoliporeanditiscoveredbyroundbracketlike
structure–Parenthesome.

10. AGGREGATION OF HYPHAE
Differenttypesofmodificationsofhyphaemyceliumarefoundas
follows:
PLECTENCHYMA -Akindoffalsetissueformedbytheaggregationof
hyphae,maybetwotypes-
A.Prosenchyma-Ratherlooselywovenhyphae,hyphaedonotlose
theiridentity,runmoreorlessparalleltoeachothercomposedof
elongatedcells,
B.Pseudoparenchyma-Thehyphaebecomewovenandintertwined
intoacompactmass,hyphalmassappearstobecontinuousstructure
consistingovalcells,resemblancewithparenchymatissueofhigher
cells
RHIZOMORPH-Interwovenhypaetoformropelikestructure,
Tightlypackedandindividualhyphaelosetheirindividualidentity,
Outerhardblackexternallayeroftherhizomporphcalledrind,,
Eachrhizomorphcontainsagrowingtip,
Rhizomorphsareperennatingstructuretowithstandadverseconditions.

11. RANGE OF THALLUS STRUCTURE

12. AGGREGATION OF HYPHAE
SCLEROTIUM-Speciallymodifiedmyceliumforstorage,
perennationandvegetativepropagation,
Compact,rounded.Cushionshaped,cylindricalorirregularobject,
Densemassofthickwalledshorthyphaetoform
pseudoparenchymatousstructure,
polyhedralshape,
Outersurfacedarkbrownblackandcrestlike,
Itmaybepinheadtolargewithseveralinchesindiameter.
SPOROPHORES -Sporebearingmodifiedintogrouptoform
pycnidia,sporodochia,hymenia,acervulietc,
Aerial,erectandarisefromtheprostratehyphae,
Branchedorunbranchedwithsporangiaorconidiawiththem,
Sporebearingsporophoresaresporangiosphoresandconidiabearing
calledconidiophores.

13. AGGREGATION OF HYPHAE
STROMATA:Thefungaltissueformsamassof
pseudoparenchymatoustissuelikeflatorcushionshapestructure,
Severalfructificationstoformreproductivestructures,
PESUDOSCLEROTIUM
Thesclerotiumlikebodiesareformedatthebaseofthefruitbodiesof
higherfungi,
InPolyporousbasilapiloidesformedbelowthesoilsurface
Composedofsandparticlessurroundedbyhyphalaggregations
APPRESORIUM
Commoninparasiticfungimostlyfoundinectoparasites,Terminal
simpleorlobedswollenstructureofgermtubesorinfectionhyphal
Adherestothesurfaceofthehostandhelpsinthepenetrationofthe
hyphaeofthepathogen,
FoundintheparasiticfungioftheordersErysiphales.

14. APPRESORIUM

15. AGGREGATION OF HYPHAE
HAUSTORIUM
Mostlyfoundintheintercellularabsorbingstructureofobligate
parasites,
Usuallyproducedinthefungiinwhichintercellularmyceliumformed,
Varyinshape,maybeknobshapedorbranchedfingershaped,
Secretecertainenzymeswhichhydrolysestheproteinsand
carbohydratesofthehostcellandabsorbthenutrientsfromthehost
cellwithoutkillingthem,
Providegreatersurfaceareafortheexchangeofmaterials.
Inadditiontotheseabovekindofmodifications,differentother
specializedmodificationsareformedinordertoaddressthestressand
otherissuesappearincourseoftheirsurvivalandreproductive
potential.

16. HAUSTORIUM

17. CELL WALL COMPOSITION
Thefungalcellwallislocatedoutsidetheplasmamembraneandisthecell
compartmentthatmediatesalltherelationshipsofthecellwiththe
environment.
Itprotectsthecontentsofthecell,givesrigidityanddefinesthecellular
structure.
Thecellwallisaskeletonwithhighplasticitythatprotectsthecellfrom
differentstresses,amongwhichosmoticchangesstandout.
Thecellwallallowsinteractionwiththeexternalenvironmentsincesomeof
itsproteinsareadhesionsandreceptors.
Since,somecomponentshaveahighimmunogeniccapacity,certainwall
componentscandrivethehost’simmuneresponsetopromotefungus
growthanddissemination.
Thecellwallisacharacteristicstructureoffungiandiscomposedmainly
ofglucans,chitinandglycoprotein.

18. CELL WALL COMPOSITION

19. CELL WALL COMPOSITION
Thecellwallisaspecificandcomplexcellularorganellecomposedof
glucans,chitin,chitosan,andglycosylatedproteins.Proteinsaregenerally
associatedwithpolysaccharidesresultinginglycoprotein.Together,these
componentscontributetothecellwallrigidity.Thesynthesisand
maintenanceofcellwallinvolvesalargenumberofbiosyntheticand
signalingpathways(CasadevallandPerfect,1998).
Thecellwallisstructuredindifferentlayerswheretheinnermostlayerisa
moreconservedstructureonwhichtheremaininglayersaredepositedand
canvarybetweendifferentspeciesoffungi.
Glucansisthemostimportantstructuralpolysaccharideofthefungalcell
wallandrepresents50–60%ofthedryweightofthisstructure.Most
polymersofglucansarecomposedof1,3linkageglucoseunits(65–90%),
althoughtherearealsoglucanswithβ-1,6(inCandidabutnotin
Aspergillus),β-1,4,α-1,3andα-1,4links.Theβ-1,3-D-glucanisthemost
importantstructuralcomponentofthewall,towhichothercomponentsof
thisstructurearecovalentlylinked.Theβ-1,3-D-glucanissynthesizedbya
complexofenzymeslocatedintheplasmamembranecalledglucans
synthases.

20. CELL WALL COMPOSITION
Thechitincontentofthefungalwallvariesaccordingtothemorphological
phaseofthefungus.Itrepresents1–2%ofthedryweightofyeastcellwall
whileinfilamentousfungi,itcanreachupto10–20%.Chitinissynthesized
fromn-acetylglucosaminebytheenzymechitinsynthase,whichdeposits
chitinpolymersintheextracellularspacenexttothecytoplasmic
membrane.
Proteinscompose30–50%ofthedryweightoffungalwallinyeastand20–
30%ofthedryweightofthewallofthefilamentousfungi.Mostproteins
areassociatedtocarbohydratesbyOorNlinkagesresultingin
glycoprotein.Cellwallproteinshavedifferentfunctionsincluding
participationinthemaintenanceofthecellularshape,adhesionprocesses,
cellularprotectionagainstdifferentsubstances,absorptionofmolecules,
signaltransmission,andsynthesisandreorganizationofwallcomponents
(BowmanandFree,2006;Ponton,2008).
Lipidsarefoundinsmallamounts,preventtodesiccationofcells,
Presenceofpigmentsandsalts;Melaninismostabundant,importantto
protectthehyphen,sporesandhelpinpathogenesis,attachmenttothe
surfaces

21. CELL WALL COMPOSITION
Enzymescrosslinkingthefibrilsinthewallarereleasedthroughtheplasma
membrane,
Wallconstrictionstakeplaceintheapicalcap;thesynthesisofchitinand
glucanstakeplacewithinin1mm.intheapex;therigidityofthewall;is
donebycrosslinkingofpolymers,
Thewallcontainshydrophobins,glomalins;Hydrophobinsconstitute10%
ofthetotalwallproteins,theamphoetricnatureprovidesanarrayofextra
ordinaryfunctionsandplayrolebiotechnology.
Glycoproteinincludesmannoprotein,galactoprotein,xyloproteinsetc.
Thewidediversityofthecellwallcompositionobservedasfarasthe
diversityofthefungalkingdomasstatedbelow.

22. COMMON WALL CONSTITUENTS IN EACH DIVISION
DIVISION FIBROUS
COMPONENTS
GEL LIKE POLYMERS
BASIDIOMYCOTINA Chitin ,β(1-3),β(1-6)
Glucans
Xylomannoproteins,α(1-3)
Glucans
ASCOMYCOTINA Chitin ,β(1-3),β(1-6)
Lucan
Galactomannoproteins, α
(1-3) Glucans
ZYGOMYCOTINA Chitin ,Chitosan Polygluchonic acid,
Glucurosomannoproteins,
Polyphosphate
CHYTRIDIOMYCOTA Chitin, Glucans Glucans

23. REVIEW
Fungi are heterotrophic either parasites, saprophytes or symbionts,
Unicellular or multicellular, holocarpic or eucarpic with diverse structural
peculiarity as far as thallus is concerned,
Eukaryotic with almost all kind of organizational beauty observed,
Cell wall is diverse type with a fundamental framework in all the aspects,
The reproduction takes place by vegetative, asexual or sexual means following
the route of plasmogamy, karyogamy & meiosis with haplontic life cycle
pattern.
Play a very significant role in the sustainability of environment and offers raw
materials for the industrial wheel,
Play a pivotal role for the deterioration of the productivity of crops both
qualitative and quantitative.

24. THANKS A LOT FOR YOUR CONSIDERATION
References:
Google for images,
Microbiology & Phycology -Mishra & Dash,
Brook Microbiology of Microorganisms-Madigan, Martinko, Bender,
Buckley & Stahl,
A Textbook of Microbiology-Chakraborty,
Microbiology-Pelzer, Chan & Krieg,
Botany for degree students-Vasistha & Sinha,
Introduction to Mycology and Phytopathology -Mishra & Dash,
Different WebPages to enrich content.
Disclaimer:ThisPPThasbeendesignedtoenrichtheopensource
oflearning.Theauthordoesnotclaimanykindoffinancialpleasure