BIOL2015–EvolutionandDiversity
Lab7:Fungi
Introduction
TheKingdomFungiconsistsoftheDivisions
Chytridiomycota,Zygomycota,Ascomycota,and
Basidiomycota.Thelatterthreegroupsare
primarilyterrestrial.Asdecomposers,withrapid
growthandhighsurface-to-volumeratio,fungi
haveanintimatecontactwiththeirenvironment
thatisverydifferentfrommostotherorganisms.
Anextensivemyceliumcanbindsoilparticles
andlitterandpenetratemostoftheuppersoil
volume.Maintenanceofthisintimatefungal
environmentrequiresthatallpartsofthefungus
bemetabolicallyactive.TheChytridiomycotawe
typicallyorderisoccasionallyunavailablesowe
maynothavetheopportunityexaminethis
group.
Fungalassociations:Lichensand
Mycorrhizae
Allfungiareheterotrophicandmostare
saprotrophic,butthehigherfungidisplayadiversityofotherrelationships.Severalspeciesof
AscomycetesandseveralBasidiomycetescombinewithgreenalgaeorevencyanobacteriatoform
lichens.Lichensareextremelywidespreadinnatureandcantoleratesevereenvironments.Theyare
evenfoundclosetotheSouthPole,oneofthedrier,coldersitesintheworld.Theyarealsoabundantin
desertsandalpineareas.Forexample,Cladoniarangiferina,alight-coloredfruticoselichenbelongingto
theCladoniaceaefamily,isanextremelyimportantfoodforcaribouandotherlargegrazersinthearctic.
Despitebeingtolerantofsevereenvironments,lichensareverysensitivetoairpollution.Lichenshave
almostdisappearedfromtheLosAngelesbasinandthereisevidencethatthelevelofpollutionhas
crossedtheinjurythresholdofthenativelichensintheSanBernardinoMountainsandthesouthern
aspectoftheSierraNevadarange.
Certainfungiplayacrucialroleinabilityofhigherplantstoacquiremineralnutrients.Thesefungiform
associationswithplantrootscalledmycorrhizae.Thefungusobtainscarbohydratesfromtheplantwhile
theplantbenefitsbecausethefungusessentiallyenlargestheirrootsystem,therebyallowingthemto
accesstothemineralnutrientsfromalargerarea.
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Evolutionaryrelationshipsanddistinguishingcharacters
Thehigherfungiappeartoberelatedtooneanother.Eachhascellwallsmadeofchitin.Themost
primitiveofthethreedivisions,Zygomycota,iscoenocytic(multinucleatecellwhichcanresultfrom
multiplenucleardivisions).InAscomycota,porousseptations(cellwalls)occur,buttheporesarelarge
enoughthatnucleicanactuallypassthrough.Theseptationsofthebasidiomyceteshaveporesgenerally
toosmallforthistooccur.Allthreegroupshavenoflagellatedorciliatedstagesandcontainno
centrioles.Additionally,themitoticspindleformsinsidethenuclearmembrane,whichdoesnotbreak
downduringnucleardivision
SexualReproduction
Sexualreproductionusuallyinvolvesthefusionoftwodistincthyphae.Inthetwomoreadvanced
divisionsthetwonucleidonotfuseimmediately;rather,afilamentwithmorethanonenucleuspercell
fromdifferentindividualsisformed.Thisisheterokaryosis.Truediploidyoccurswhenthenucleifuse.
Meiosisusuallyoccursimmediatelyafterwardsresultingintheformationofhaploidspores.The
resultinghaploidsporesgerminatetoformnewmycelia.Membersofallthreegroupsoftenproduce
specialstructurestoaidsporedispersal.Forexample,amushroomisanexampleofa"fruiting"body
(composedofmanyheterokaryoticcells)fromwhichsporesdisperseinsomebasidiomycetes.
Examples
Someimportantorfamiliargenerainclude:Rhizopus,thecommonbreadmold,aZygomycete;Claviceps
purpurea,ergot,aplantparasitethatcausessevereillnessordeathinhumans,anascomycete;
Penicillium,anascomycetegenuswithinwhichsomefermentingspeciesformcheeses,whileothersare
thesourceoftheantibioticpenicillin.Yeasts(Saccharomyces)areunicellularascomyceteswhich
fermentsugarsintheproductionofalcoholicbeersandwines,aswellasbread;trufflesandmorels,
reproductivestructuresofvariousascomycetespecies,areprizedasgourmetfoods.Amanitaisa
familiarbasidiomycetethatkillsamateurmushroomcollectorseachyearafterthecollectorseatthe
fruitingbody,unawarethatitishighlytoxic.
Duringthislabfocusontheappearanceandstructureofthehyphae,asthisisthebasicformofthe
organism.Examinecarefullythereproductivestructures.Becausefungiareusuallyfilamentousand
growinsoil,wood,anddetritusmaterials,muchofourfamiliaritywiththemislimitedtotheir
reproductivestructures.
Zygomycota
Rhizopus
Thisfungusisdistributedthroughouttheworld.Onespeciesisusedtofermentriceintosake.Another
speciesisusedtoinoculatesoybeanstomaketempeh.Thegenusisusuallysaprophyticbutfrequently
attacksfruitsandvegetablesthathavebeeninjured.Itoccupiesnon-aquatichabitatsandnever
producesmotilespores.Sexualreproductionisbyconjugation.
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(A)Examinationofpreparedslide
Findapreparedslidelabeled“Rhizopusconjugation”.Whenyouobservethepreparedslide,tryto
observethedifferentstagesinthedevelopmentofzygosporangia–especiallythestagewherethe
gametangiahaveformed.
(B)Cultureexamination
(1)ExamineacultureofRhizopus.Notetheappearanceofthecolony.Whatcolorarethehyphae?What
otherstructurescanyousee?
(2)Examinetheculturewithadissectingmicroscope.Isthemyceliumbranched?Arecrosswalls
present?Notethecharacteristicformationofrhizoids,thesmallroot-likebranchesalongthehyphae
growingonthesubstrate.
(3)Focusonthedarkcoloredstructures.These
aresporangia.Thedarkonescontainmassesof
maturesporangiospores(Figure1).Thewhitish
onesarenotyetmature.Thesporangialwallis
veryfragileandisfrequentlyrupturedwhen
preparingslides.Thebranchsupportingthe
sporangiumiscalledasporangiophore.
(C)WetMount
Prepareawetmountofsomeofthemycelium
withsporangiaandexaminewithacompound
microscope.Notethecoenocyticmycelium.
Locateasporangiophoreandsporangium.
Whatcolorarethespores?Isthespore
wallsmoothorroughened?
Figure1
(D)SexualReproduction
(1)Todemonstratesexualreproduction,2differentstrainsofRhizopushavebeengrowntogether.
Examineaplatewithadissectingmicroscope.Findanearlystageofconjugationinwhichshort,lateral
branchesarisefromseparatehyphaeandcomeintocontact.Thebranchestypicallybecomeenlarged
andhavearelativelydensemassof
cytoplasm.Theyaretheprogametangia.
(2)Nextfindstagesinwhichacrosswallhas
dividedtheprogametangiaintoaterminal
portion,thegametangium(Figure2a,left
panel,toparrow)andasupportingcell
calledsuspensor.
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Figure2a
(3)Thewallseparatingtheplus(+)andminus(-)gametangiadissolves,thecytoplasmmixes,andnuclei
pair.Nuclearfusionoccursandthecellformedbytheformergametangiadevelopsathick,darkcolored,
roughwall.Thisisthezygospore(Figure2a,leftpanel,middlearrow).Itcanremaindormant,but
eventuallymeiosisoccurs.Asporangiumarisesfromthezygospore,afterwhichthehaploidspores
disperse.
Pilobolus
Thisfungusiscommonlyfoundinpasturesgrowingondung(Figure
2b).Thesporangiophoresarephototrophicandcanshootthe
sporangiaupto2-3metersinthedirectionofabrightlightsource.
(1)ExaminethelivingculturesofPiloboluscrystallinus.Whatisthe
adaptivesignificanceofhavingphototrophicsporangiophores?
Figure2b
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Ascomycota
Saccharomyces-yeast
Yeastsconsistofasingle,non-motilecell.Theseorganismsreproduceasexuallybybuddinginwhich
daughtercellsareformedatoneorbothendsoftheparentcell.Insexualreproductiontheentirecell
becomesanascuswitheitherfouroreightascospores.Manyoftheyeastssuchasthisoneareof
considerableeconomicimportancetohumans–theyproducecarbondioxidetoLevinbreadunder
aerobicconditionsoralcoholunderanaerobicconditions.
Prepareaslidefromoneofthefermentingculturesandexamineunderhighpoweroroilimmersion.
(1)Notetheshapeandsizeofthecells.Makesureyouwillbeabletodistinguishthemfromothercells.
(2)Lookforbuddingcells.Thesmallcellcontinuestoincreaseinsizeuntilitreachesthesizeofthe
parentandeventuallybreaksfree.Beforebecomingfree,however,itmighthavebeguntobud;thusit
isn'tuncommontoseechainsof2-4cellsinvariousstagesofbudding.
PenicilliumandAspergillus
Thesetwokindsoffungiareextremelycommonandare,infact,
laboratory"weeds".Althoughtheyareascomycetes,onlyasexual
stageswillbeexamined.
Findapreparedslidelabeled"MoldTypes"or"Penicillium,
Aspergillus,Rhizopus"
(1)Examinethedemonstrationculturessetupforyou.Isthe
myceliumseptate?Asexualreproductionoccurswiththe
formationofconidiosporesatthetipsofanerectbranchcalled
theconidiophore(Figure3).Aretheythesameinbothgenera?In
someascomycetes,thetipoftheconidiophorehasanenlarged
Figure3
cellcalledthevesicle,towhichareattachedshortbranches
calledsterigmata(Figure3,arrow).Theconidiosporescanbe
foundattachedtotheendsofthesterigmata.Inothersthesterigmatamaybebranchedaswell.
(2)WhatistherelationshipbetweenPenicilliumandpenicillin?
Eurotiumchevalieri
Findalivingculture.Youwillseesmall,roundstructuresyellowincolorunderadissectingmicroscope.
Thesearethecleistothecia-ascocarpsthatcompletelyenclosethematureasciandreleasethe
ascocporeswhentheyruptureordegrade.Youmayalsoseesmallfuzzystructures(conidiaand
conidiophoreslikethoseinAspergillus).
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Basidiomycota
Thesefungiareregardedasamongthemore
advancedbasidiomycetesbecauseof
thebasidiumandthefleshyfruitingbody.
(1)Findthefollowingonafresh
mushroom:pileus(cap);stipe(stalk);lamellae(gills)
;annulus(collar);volva(cup).Whatistheoriginof
theannulusandvolva?(answer:remnantofthe
partialveil-Asheetoftissueunderamushroom
cap.Itstretchesfromthecapmargintothestem,
andprotectsthesporebearingtissuesuntilthe
sporesaremature).Besureyoucanfindthemonall
thefreshmushrooms,includingAgaricusbisporus,
commonbuttonmushroom.
Cutoneofthesemushroomsinhalf,vertically,and
leaveonehalfforsomeoneelsetouse.Carefully
removeoneofthegillsandmountonaslideina
dropofwater,pressingdownonthecoverslipto
keepitflat.Findtheterminalbranch-likestructures
(sterigmata),towhichareattached
thebasidiospores.Howmanybasidiosporesarein
eachbasidium?Notedifferencesinspore
coloramongdifferentspecies.
Figure4
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Lichens
Lichensareformedbyasymbioticassociationofafungusandanalga.Thefungusinmostlichenspecies
isanascomycota,butinsomelichensitisabasidiomycota.Thealgaisoneofseveraldistinctspeciesof
ChlorophytaorCyanobacteria.Thealgafromthisassociationcanusuallysurviveasafree-living
organism,butthefunguscannot.Thealgaprovidesfoodforthefungus,andthefungusfurnishes
moisture,shelter,andmineralsforthealga.
Figure5:crustose(left),foliose(middle),andfruticose(right)morphsoflichen
Vegetativestructure
Examinespeciesoflichensthatdemonstratethethreegeneraltypesoflichengrowthforms:crustose,a
flattened,crust-likeform;foliose,amoreorlessleaf-likeappearance;andfruticose,orabranching,
shrub-likeform.
Reproductivestructures-Sexualreproductionofthefungalpartner
Onthespecimensavailable,notewhetherthereareanyfruitingbodiesassociatedwiththem.Theseare
oftenbrightlycolored.Becausemostlichensareascomycetes,thesefruitingbodiesarelikelytobe
ascocarps,reproductivestructurescontaininglargenumbersofasciarrangedonapothecia(thecups).A
preparedslideisavailabletoshowyouathinsectionofthisarea.
Asexualreproductionofthelichen
Carefullyexaminethesurfaceofthelichens
forsorediaorisidia.Surveythesurfaceofthelichen
untilyoufindanareawhichseemstobecoveredwith
alightdustonitandisassociatedwithcracksor
openingsthroughtheupperlichencortex.Examine
theseareascarefullyandyoushouldbeableto
observesoredia,whicharespecializedfragmentsof
thelichencontainingafewalgalcellsandsurrounded
byhyphae.Otherlichensdisplayisidia,whicharetiny
branchesonthesurfaceofthelichen.Thesebranches
areactuallyimmaturethalli,alreadywithanupper
andlowercortexandcontainingalgalcells.Bythese
Figure6
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means,lichensareabletopropagateandactuallymaintainbothmembersofthesymbiosis.Canyou
thinkofawaybothmemberscansexuallyreproduceanddispersetheirprogenywhilecontinuingto
maintainasymbioticrelationship?
Mycorrhizae
Certainsoilfungiformassociationswithrootsofvascularplants.Theassociationappearstobenefitboth
membersbecausestudieswithradioactivetracershaveshownthatthefungusreceivescarbohydrates
fromthegreenplantwhiletherootsobtainmineralnutrientsthatthefungushasabsorbedfromthe
soil.Thesemycorrhizalassociationsarewidespreadthroughoutthevascularplantkingdomandsofar
havebeenfoundinover80%ofthefloweringplantsexamined.
(A)EctomycorrhizaeandEndomycorrhizae
Thetwocommontypesofmycorrhizaeareectomycorrhizaeandendomycorrhizae.Ectomycorrhizaeare
characteristicofcertaintemperatetreessuchasoaks,willows,andconifers.Theyformasheath
surroundingtheroottipswithhyphaepenetratingbetweenthecellsoftherootcortex.Roottipswith
ectomycorrhizaetakeonacharacteristicappearance,shorterandstubbierthanuninfectedrootsand
oftenforming"Y"branches.Ectomycorrhizalfungiareusuallybasidiomycetes,oroccasionally
ascomycetes.
Findapreparedslidelabeled"EctotrophicMycorrhiza"andnotethecharacteristicbranchingpattern.
Endomycorrhizaearecommonlyfoundonherbaceousplants,manytropicalandsometemperatetrees.
Themyceliumpenetratesthecellsoftheplantrootcortexinthisassociationandformslargevesiclesor
branchingsystemswithinthecells.Endomycorrhizalfungiarezygomycetes.Besureyoucandistinguish
ecto-versusendomycorrhizae.
Findapreparedslidelabeled"EndotrophicMycorrhiza"andmakesureyoucandistinguishthefungal
hyphaeamongthecorticalcellsoftheroot.
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