Life-cycle-of-Sphagnum.pdf

This is a Life Cycle of Shpagnum, A good content for Masters Students. (But this content is not made by me...but i thought that this will help many students who are in search for content)
Thank you 😊

1. Bhagalpur National College, Bhagalpur
( A Constituent unit of Tilka Manjhi Bhagalpur University, Bhagalpur)
PPT Presentation for B.Sc. I-Life Cycle of Sphagnum
Presented by -Dr. AmitKishoreSingh
Department of Botany
B.N. College, Bhagalpur

2. Kingdom-Plantae (Plant)
Division-Bryophyta
Class-Musci (Moss)
Order-Sphagnales
Family-Sphagnaceae
Genus-Sphagnum

3. •Sphagnumispopularlyknownasbogmoss,peatmossorturfmossbecauseof
itsecologicalimportanceinthedevelopmentofpeatorbog.
•Theplantsareperennialandgrowinswampsandmoisthabitatlikerockyslopes
wherewateraccumulatesorwherewaterdrips.
Structure of Sphagnum
•ThegametophytephaseofSphagnumisrepresentedbytwodistinctstages
namely,(a)juvenileprotonema,and(b)matureleafyorgametophorestage.
•Veryyounggameto­phytesbearmulticellularrhizoidswithobliquesepta.
•Maturegametophytes,how­ever,donotbearrhizoids.
•Gametophyteisdifferentiatedintoanuprightbranchedaxisandleaves.
External Morphology

4. Main Axis and Branches:
•Themainaxisissoftandweakatyoungstage,butbecomeserectandstoutat
maturity.However,themainaxisismuchlongerinaquaticspecies,butisrelatively
shortinterrestrialformduetotheprogressivedeathoftheolderbasalpart.
•Theaxisbranchesprofuselyonthelateralsides.Singlebranchorintuftsof3to8
branchesarisefromtheaxilsofeveryfourthleafofthemainaxis.
•Attheapexofthemainstem,manysmallbranchesoflimitedgrowtharedensely
crowdedformingacompactheadcalledcoma.
•Thecomaisformedneartheapexduetothecondensedgrowthofapical
internodes.Asthestemgrowsinlengththeseshortbrancheselongateandbecome
normalbranches.
•Theterrestrialspeciespro­ducetwotypesofbranchesviz.,(i)pendentbranches,
and(ii)upwardlydivergentbranches.

6. Pendent Branches
•Thesearelongslenderlooselyarranged,turndownwardsandthengrowparalleltothe
mainaxis.Theyarealsotermedflagelliformorde-currentbranches.
Divergent Branches
•Theseareshortandstoutbrancheswhichgrowoutwardsandupwards.Theyarealso
termedex-currentbran­ches.Sometimes,onedivergentbranchineachnodedevelops
stronglythanothersandultimate­lygivesrisetoanewplantwhenitbecomesdetached
fromthemotherplant.
Leaves
•Theleavesoccurbothonthemainaxisaswellasonthebranches(Fig.6.38C).Onthe
branches,theleavesarecloselysetand,there­fore,overlappingandareplacedaparton
themainaxis.Theleavesarearrangedinspiralphyllotaxy.
•Ingeneral,theleavesaresmall,sessile,entire,thinandscale­-likewithacuteapexand
withoutamidrib.

7. Internal structure
•T.S.ofstemshows3regions.Theoutercortexorhyalodermisisabout3-6layersof
compactlyarrangedcells,inolderstems.Itstoreswater.hematurecorti­calcellisdevoid
ofprotoplasm.Insomespecies(S.tenellum,S.molluscum),someoutercorticalcells
enlargepeculiarlyandbecomebottleorretort-shaped.Theneckofeachcellisturned
outwardawayfromtheaxisandhasaporeatthedistalend.Thesearecalledretortcells.
Theyaccumulatewaterandinhabitedbysmallmicroscopicanimals.
•Themiddleregionishadrome.Itcomprisesofprosenchymatouscells.Itprovides
mechanicalsupport.
•Theinnermostregionismedulla,madeupofcolourlessparenchymatouscells.
T.S. of Stem

8. T.S. of leaf
•Leavesofsphagnumareuniqueinstructure.Theyhaveasinglelayerofcellsinthickness.
Thecellsareoftwotypes:Narrow,chlorophyllcontainingcellsarecalledassimilatorycells/
cholorophyllouscells.
•Theassimilatorycellsaresmalltriangularorbiconvexlivingcellswithmanydiscoid
chloroplastsandhavetheirphotosyntheticability
•Large,rhomboidaldeadcellsarecalledhyalinecells.Thesetwotypesofcellsarearranged
alternativelyintheleaf,toformanet-likestructure.
•Thehyalinecellshavearemar­kablecapacityofabsorptionandretentionofwater.

9. II.Sexual Reproduction:
•Itisadvancedoogamoustype.Antheridiaandarchegoniaareproducedinspecialbranches
calledantheridialormaleandarchegonialorfemalebranches,insame(monoecious)or
different(dioecious)plants.Thesebranchesoccuratthetipofthestem(inthecoma)orat
thelowernodes.
•Structureofantheridialbranchandantheridia:Antheridialbranchesareshorterthanthe
vegetativebranchesandappearlikecatkins.Theyarecoveredwithred/browncoloured
leaves.
Antheridiaarearrangedacropetallyintheaxilsoftheleavesofthesebranches.
Antheridiaareclubshapedwithalong,multicellularstalkandaglobularbody.
Thebodyiscoveredwithasinglelayeredjacketwhichsurroundsnumerousandrogonial
cells.
Theandrogonialcellsdevelopintoantherozoidsorsperms.
Eachspermisspirallycoiled,elongatedstructurewithapairofflagella.
Maturespermsarereleasedfromtheantheridiumbythe
separationofthejacketcells.

11. Structure of archegonial branch and archegonia:
•Thearchegonialbranchesareveryshortandthick.Theyarepurpleincolour.Theyare
coveredwithlargeleavescalledperichaetialleaves.Goupsof3-5archegoniaarefoundatthe
tipoftheeachbranch.
Thematurearchegoniumisflaskshapedwithalongtwistedneckandaswollenventer.
Theneckiscoveredwith6verticalrowsofneckcellsandcovercells.Itencloses8-9neck
canalcells.
Theventeriscoveredby2-3layersofcells.Itenclosesaventercanalcellandabasalegg
cell.

12. Fertilization
•Theprocessoffertilisationtakesplaceonlyinthepresenceofwater.
•Theantherozoidsswimfreelyinwaterandreachthearchegonia.Atmaturity,theneckcanal
cellsandtheventralcanalcelldisorganiseandformapassagefortheantherozoids.
•Theantherozoidsreachnearthearchegoniaattractedchemotacticallyandpassintothe
passagetoreachtheegg.Ultimately,onlyoneantherozoidfuseswiththeeggandformsa
zygote(2n).
Sporophyte
Development of the Sporophyte
•Thediploidzygoteisthefirstcellofthesporophyticgeneration.Amongthefewarchegonia
onlyoneisdevelopedtoformembryoinanarchegonialbranch.
•Thezygoteenlargesandundergoestransversedivisiontoform6-or7-celledfilamentous
structure.
•Thelowerhalfofthefilamentundergoesirregulardivisionsformingaparenchymatous
bulbousfoot.Thefootactsasahaustoriumandobtainfoodfromarchegoniumuntill
completedevelopment.

13. •Theuppercellsofthefilamentdividebytwoverticaldivisionsatrightangletoeachother
—aquadrantisformed.Thecellsofthequad­rantdividepericlinallytoformaninner
endotheciumandanouteramphithecium.
•Thecellsoftheendotheciumrepeatedlydivideandformacentralsterilepart,columella.
•Theamphitheciumdividesperi­clinallytodifferentiateaninner2-4layeredarchesporium
andtheouter3-7layeredcapsulewall.
•Thearchesporiumformsadome-shapedarchoverthecolumella.
•Thecellsofthearchesporiumlaterdevelopinto2-4layeredsporogenoustissue.
•Allsporogenouscellsfunctionassporemothercellsthatdividemeioticallyandform
haploidspores.Thesporesareenclosedwithinasporesacdevelopedfromthe
surroun­dingsteriletissue.
•Thereisonlyashortnecklikeinconspicuoussetaconnectingtheuppercapsuleandthe
lowerbulbousfoot.

14. Structure of Sporophyte
Theripesporophyteisadarkbrownish-blackcolouredsphericalstructureappearingatthetip
ofthefemalebranch.ItisfoundonastalkcalledtheThematuresporophyteconsistsofa
bulbousfootandasphericalcapsule.Thetwoareconnectedbyanarrowneck-likeregion
whichrepresentstheseta.Thefootisembeddedinthetissueofthepseudopodiumofthe
gametophyte.Itabsorbsnutritionandwaterforthegrowingsporophyte.Thecapsulehasthe
followingparts:
•Amassivecentralcolumnofsterilecellscalledcolumella.
•Athindomeshapedsporesacoverarchingthecolumella.Itcontainshaploidspores.
•Elatersareabsent.
•The4-6layeredcapsulewallsurroundsthecolumellaandsporesac.Itsouterlayeris
calledepidermisanditconsistsofmanynon-functionalstomata.
•Aconvexdisc-shapedoperculumorlidisfoundatthetopofthecapsule.Itisseparated
fromtherestofthecapsulebyaringlikegrooveofthincellscalledannulus.
•Theremainsofarchegoniaformacalyptrawhichcoverthetipofcapsule.
•Whenthesporophyteismature,theoperculumisblownoffforcefully,bytherupturing
oftheannuluscells.Thesporesarealsoreleasedintotheairlikeacloud.
•

16. Dehiscence of the Capsule
•Thecapsuledehiscesonabrightsunnydaybyanexplosivemechanism.Thecapsulewall
andcolumellabecomedryandshrivelduetoheat.Thisresultsintheformationofalargeair
spacebelowthespore-sac.
•Thesphericalcapsulegraduallybecomescylindricaland,therefore,anover­pressureof4-6
atmospheresbuildsupinsidethecapsule.Underthisconditionitsoperculumburstsopen
throughtheannuluswithanaudiblesound.Thesporesarecatapultedupto20cmand
releaseintheair.Theprocessisknownasair-gunmechanismofsporedis­persal.
Germination of spores
•Likeotherbryophytes,thesporeisthefirstcellofthegametophyticgeneration.
•Initially,thesporesarearrangedintetrahedraltetrads.Eachsporehasadistincttriradiate
ridge.
•Thewallofthesporeisdifferentiatedintoanoutersmoothgranularorpapillateexineand
aninnerthinintine.
•Thesporesgerminatewhentheconditionsarefavorabletodevelopintoagreen,flat,
irregularlylobed,thalluslikestructurecalledprimaryprotonema.Itisphotosyntheticand
bearsrhizoids.Fromthemarginalcellsofthisprotonema,abudlikestructuredevelopswhich
furthergrowtoformtheyoungerectgametophyte.

17. Germination of spores into new gametophyte