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BIOL2015–EvolutionandDiversityLab6:Fungi

Introduction

TheKingdomFungiconsistsoftheDivisionsChytridiomycota,Zygomycota,Ascomycota,andBasidiomycota.Thelatterthreegroupsareprimarilyterrestrial.Asdecomposers,withrapidgrowthandhighsurface-to-volumeratio,fungihaveanintimatecontactwiththeirenvironmentthatisverydifferentfrommostotherorganisms.Anextensivemyceliumcanbindsoilparticlesandlitterandpenetratemostoftheuppersoilvolume.Maintenanceofthisintimatefungalenvironmentrequiresthatallpartsofthefungusbemetabolicallyactive.TheChytridiomycotawetypicallyorderisoccasionallyunavailablesowemaynothavetheopportunityexaminethisgroup.

Fungalassociations:LichensandMycorrhizae

Allfungiareheterotrophicandmostaresaprotrophic,butthehigherfungidisplayadiversityofotherrelationships.SeveralspeciesofAscomycetesandseveralBasidiomycetescombinewithgreenalgaeorevencyanobacteriatoformlichens.Lichensareextremelywidespreadinnatureandcantoleratesevereenvironments.TheyareevenfoundclosetotheSouthPole,oneofthedrier,coldersitesintheworld.Theyarealsoabundantindesertsandalpineareas.Forexample,Cladoniarangiferina,alight-coloredfruticoselichenbelongingtotheCladoniaceaefamily,isanextremelyimportantfoodforcaribouandotherlargegrazersinthearctic.Despitebeingtolerantofsevereenvironments,lichensareverysensitivetoairpollution.LichenshavealmostdisappearedfromtheLosAngelesbasinandthereisevidencethatthelevelofpollutionhascrossedtheinjurythresholdofthenativelichensintheSanBernardinoMountainsandthesouthernaspectoftheSierraNevadarange.

Certainfungiplayacrucialroleinabilityofhigherplantstoacquiremineralnutrients.Thesefungiformassociationswithplantrootscalledmycorrhizae.Thefungusobtainscarbohydratesfromtheplantwhiletheplantbenefitsbecausethefungusessentiallyenlargestheirrootsystem,therebyallowingthemtoaccesstothemineralnutrientsfromalargerarea.

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Evolutionaryrelationshipsanddistinguishingcharacters

Thehigherfungiappeartoberelatedtooneanother.Eachhascellwallsmadeofchitin.Themostprimitiveofthethreedivisions,Zygomycota,iscoenocytic(multinucleatecellwhichcanresultfrommultiplenucleardivisions).InAscomycota,porousseptations(cellwalls)occur,buttheporesarelargeenoughthatnucleicanactuallypassthrough.Theseptationsofthebasidiomyceteshaveporesgenerallytoosmallforthistooccur.Allthreegroupshavenoflagellatedorciliatedstagesandcontainnocentrioles.Additionally,themitoticspindleformsinsidethenuclearmembrane,whichdoesnotbreakdownduringnucleardivision

SexualReproduction

Sexualreproductionusuallyinvolvesthefusionoftwodistincthyphae.Inthetwomoreadvanceddivisionsthetwonucleidonotfuseimmediately;rather,afilamentwithmorethanonenucleuspercellfromdifferentindividualsisformed.Thisisheterokaryosis.Truediploidyoccurswhenthenucleifuse.Meiosisusuallyoccursimmediatelyafterwardsresultingintheformationofhaploidspores.Theresultinghaploidsporesgerminatetoformnewmycelia.Membersofallthreegroupsoftenproducespecialstructurestoaidsporedispersal.Forexample,amushroomisanexampleofa"fruiting"body(composedofmanyheterokaryoticcells)fromwhichsporesdisperseinsomebasidiomycetes.

Examples

Someimportantorfamiliargenerainclude:Rhizopus,thecommonbreadmold,aZygomycete;Clavicepspurpurea,ergot,aplantparasitethatcausessevereillnessordeathinhumans,anascomycete;Penicillium,anascomycetegenuswithinwhichsomefermentingspeciesformcheeses,whileothersarethesourceoftheantibioticpenicillin.Yeasts(Saccharomyces)areunicellularascomyceteswhichfermentsugarsintheproductionofalcoholicbeersandwines,aswellasbread;trufflesandmorels,reproductivestructuresofvariousascomycetespecies,areprizedasgourmetfoods.Amanitaisafamiliarbasidiomycetethatkillsamateurmushroomcollectorseachyearafterthecollectorseatthefruitingbody,unawarethatitishighlytoxic.

Duringthislabfocusontheappearanceandstructureofthehyphae,asthisisthebasicformoftheorganism.Examinecarefullythereproductivestructures.Becausefungiareusuallyfilamentousandgrowinsoil,wood,anddetritusmaterials,muchofourfamiliaritywiththemislimitedtotheirreproductivestructures.

Zygomycota

Rhizopus

Thisfungusisdistributedthroughouttheworld.Onespeciesisusedtofermentriceintosake.Anotherspeciesisusedtoinoculatesoybeanstomaketempeh.Thegenusisusuallysaprophyticbutfrequentlyattacksfruitsandvegetablesthathavebeeninjured.Itoccupiesnon-aquatichabitatsandneverproducesmotilespores.Sexualreproductionisbyconjugation.

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(A)Examinationofpreparedslide

Findapreparedslidelabeled“Rhizopusconjugation”.Whenyouobservethepreparedslide,trytoobservethedifferentstagesinthedevelopmentofzygosporangia–especiallythestagewherethegametangiahaveformed.

(B)Cultureexamination

(1)ExamineacultureofRhizopus.Notetheappearanceofthecolony.Whatcolorarethehyphae?Whatotherstructurescanyousee?

(2)Examinetheculturewithadissectingmicroscope.Isthemyceliumbranched?Arecrosswallspresent?Notethecharacteristicformationofrhizoids,thesmallroot-likebranchesalongthehyphaegrowingonthesubstrate.

(3)Focusonthedarkcoloredstructures.Thesearesporangia.Thedarkonescontainmassesofmaturesporangiospores(Figure1).Thewhitishonesarenotyetmature.Thesporangialwallisveryfragileandisfrequentlyrupturedwhenpreparingslides.Thebranchsupportingthesporangiumiscalledasporangiophore.

(C)WetMount

Prepareawetmountofsomeofthemyceliumwithsporangiaandexaminewithacompoundmicroscope.Notethecoenocyticmycelium.Locateasporangiophoreandsporangium.Whatcolorarethespores?Isthesporewallsmoothorroughened?

(D)SexualReproduction

(1)Todemonstratesexualreproduction,2differentstrainsofRhizopushavebeengrowntogether.Examineaplatewithadissectingmicroscope.Findanearlystageofconjugationinwhichshort,lateralbranchesarisefromseparatehyphaeandcomeintocontact.Thebranchestypicallybecomeenlargedandhavearelativelydensemassofcytoplasm.Theyaretheprogametangia.

(2)Nextfindstagesinwhichacrosswallhasdividedtheprogametangiaintoaterminalportion,thegametangium(Figure2a,leftpanel,toparrow)andasupportingcellcalledsuspensor.

Figure2a

Figure1

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(3)Thewallseparatingtheplus(+)andminus(-)gametangiadissolves,thecytoplasmmixes,andnucleipair.Nuclearfusionoccursandthecellformedbytheformergametangiadevelopsathick,darkcolored,roughwall.Thisisthezygospore(Figure2a,leftpanel,middlearrow).Itcanremaindormant,buteventuallymeiosisoccurs.Asporangiumarisesfromthezygospore,afterwhichthehaploidsporesdisperse.

Pilobolus

Thisfungusiscommonlyfoundinpasturesgrowingondung(Figure2b).Thesporangiophoresarephototrophicandcanshootthesporangiaupto2-3metersinthedirectionofabrightlightsource.

(1)ExaminethelivingculturesofPiloboluscrystallinus.Whatistheadaptivesignificanceofhavingphototrophicsporangiophores?

Figure2b

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Ascomycota

Saccharomyces-yeast

Yeastsconsistofasingle,non-motilecell.Theseorganismsreproduceasexuallybybuddinginwhichdaughtercellsareformedatoneorbothendsoftheparentcell.Insexualreproductiontheentirecellbecomesanascuswitheitherfouroreightascospores.Manyoftheyeastssuchasthisoneareofconsiderableeconomicimportancetohumans–theyproducecarbondioxidetoLevinbreadunderaerobicconditionsoralcoholunderanaerobicconditions.

Prepareaslidefromoneofthefermentingculturesandexamineunderhighpoweroroilimmersion.

(1)Notetheshapeandsizeofthecells.Makesureyouwillbeabletodistinguishthemfromothercells.

(2)Lookforbuddingcells.Thesmallcellcontinuestoincreaseinsizeuntilitreachesthesizeoftheparentandeventuallybreaksfree.Beforebecomingfree,however,itmighthavebeguntobud;thusitisn'tuncommontoseechainsof2-4cellsinvariousstagesofbudding.

PenicilliumandAspergillus

Thesetwokindsoffungiareextremelycommonandare,infact,laboratory"weeds".Althoughtheyareascomycetes,onlyasexualstageswillbeexamined.

Findapreparedslidelabeled"MoldTypes"or"Penicillium,Aspergillus,Rhizopus"

(1)Examinethedemonstrationculturessetupforyou.Isthemyceliumseptate?Asexualreproductionoccurswiththeformationofconidiosporesatthetipsofanerectbranchcalledtheconidiophore(Figure3).Aretheythesameinbothgenera?Insomeascomycetes,thetipoftheconidiophorehasanenlargedcellcalledthevesicle,towhichareattachedshortbranchescalledsterigmata(Figure3,arrow).Theconidiosporescanbefoundattachedtotheendsofthesterigmata.Inothersthesterigmatamaybebranchedaswell.

(2)WhatistherelationshipbetweenPenicilliumandpenicillin?

Eurotiumchevalieri

Findalivingculture.Youwillseesmall,roundstructuresyellowincolorunderadissectingmicroscope.Thesearethecleistothecia-ascocarpsthatcompletelyenclosethematureasciandreleasetheascocporeswhentheyruptureordegrade.Youmayalsoseesmallfuzzystructures(conidiaandconidiophoreslikethoseinAspergillus).

Figure3

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Basidiomycota

Thesefungiareregardedasamongthemoreadvancedbasidiomycetesbecauseofthebasidiumandthefleshyfruitingbody.

(1)Findthefollowingonafreshmushroom:pileus(cap);stipe(stalk);lamellae(gills);annulus(collar);volva(cup).Whatistheoriginoftheannulusandvolva?(answer:remnantofthepartialveil-Asheetoftissueunderamushroomcap.Itstretchesfromthecapmargintothestem,andprotectsthesporebearingtissuesuntilthesporesaremature).Besureyoucanfindthemonallthefreshmushrooms,includingAgaricusbisporus,commonbuttonmushroom.

Cutoneofthesemushroomsinhalf,vertically,andleaveonehalfforsomeoneelsetouse.Carefullyremoveoneofthegillsandmountonaslideinadropofwater,pressingdownonthecoversliptokeepitflat.Findtheterminalbranch-likestructures(sterigmata),towhichareattachedthebasidiospores.Howmanybasidiosporesareineachbasidium?Notedifferencesinsporecoloramongdifferentspecies.

Figure4

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Lichens

Lichensareformedbyasymbioticassociationofafungusandanalga.Thefungusinmostlichenspeciesisanascomycota,butinsomelichensitisabasidiomycota.ThealgaisoneofseveraldistinctspeciesofChlorophytaorCyanobacteria.Thealgafromthisassociationcanusuallysurviveasafree-livingorganism,butthefunguscannot.Thealgaprovidesfoodforthefungus,andthefungusfurnishesmoisture,shelter,andmineralsforthealga.

Vegetativestructure

Examinespeciesoflichensthatdemonstratethethreegeneraltypesoflichengrowthforms:crustose,aflattened,crust-likeform;foliose,amoreorlessleaf-likeappearance;andfruticose,orabranching,shrub-likeform.

Reproductivestructures-Sexualreproductionofthefungalpartner

Onthespecimensavailable,notewhetherthereareanyfruitingbodiesassociatedwiththem.Theseareoftenbrightlycolored.Becausemostlichensareascomycetes,thesefruitingbodiesarelikelytobeascocarps,reproductivestructurescontaininglargenumbersofasciarrangedonapothecia(thecups).Apreparedslideisavailabletoshowyouathinsectionofthisarea.

Asexualreproductionofthelichen

Carefullyexaminethesurfaceofthelichensforsorediaorisidia.Surveythesurfaceofthelichenuntilyoufindanareawhichseemstobecoveredwithalightdustonitandisassociatedwithcracksoropeningsthroughtheupperlichencortex.Examinetheseareascarefullyandyoushouldbeabletoobservesoredia,whicharespecializedfragmentsofthelichencontainingafewalgalcellsandsurroundedbyhyphae.Otherlichensdisplayisidia,whicharetinybranchesonthesurfaceofthelichen.Thesebranchesareactuallyimmaturethalli,alreadywithanupperandlowercortexandcontainingalgalcells.Bythese

Figure5:crustose(left),foliose(middle),andfruticose(right)morphsoflichen

Figure6

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means,lichensareabletopropagateandactuallymaintainbothmembersofthesymbiosis.Canyouthinkofawaybothmemberscansexuallyreproduceanddispersetheirprogenywhilecontinuingtomaintainasymbioticrelationship?

Mycorrhizae

Certainsoilfungiformassociationswithrootsofvascularplants.Theassociationappearstobenefitbothmembersbecausestudieswithradioactivetracershaveshownthatthefungusreceivescarbohydratesfromthegreenplantwhiletherootsobtainmineralnutrientsthatthefungushasabsorbedfromthesoil.Thesemycorrhizalassociationsarewidespreadthroughoutthevascularplantkingdomandsofarhavebeenfoundinover80%ofthefloweringplantsexamined.

(A)EctomycorrhizaeandEndomycorrhizae

Thetwocommontypesofmycorrhizaeareectomycorrhizaeandendomycorrhizae.Ectomycorrhizaearecharacteristicofcertaintemperatetreessuchasoaks,willows,andconifers.Theyformasheathsurroundingtheroottipswithhyphaepenetratingbetweenthecellsoftherootcortex.Roottipswithectomycorrhizaetakeonacharacteristicappearance,shorterandstubbierthanuninfectedrootsandoftenforming"Y"branches.Ectomycorrhizalfungiareusuallybasidiomycetes,oroccasionallyascomycetes.

Findapreparedslidelabeled"EctotrophicMycorrhiza"andnotethecharacteristicbranchingpattern.

Endomycorrhizaearecommonlyfoundonherbaceousplants,manytropicalandsometemperatetrees.Themyceliumpenetratesthecellsoftheplantrootcortexinthisassociationandformslargevesiclesorbranchingsystemswithinthecells.Endomycorrhizalfungiarezygomycetes.Besureyoucandistinguishecto-versusendomycorrhizae.

Findapreparedslidelabeled"EndotrophicMycorrhiza"andmakesureyoucandistinguishthefungalhyphaeamongthecorticalcellsoftheroot.