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SE X U A L REP R ODUCTIO N IN F L OWERIN G PLANTS

SE X U A L REP R ODUCTIO N IN F L OWERIN G PLANTS. P r e fer t iliza t ion : s t ructu r e an d e v en t s:. Hormonal and structural changes in plants leads to development of flower, Androecium consists of a whorl of stamens represents male sex organ.

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SE X U A L REP R ODUCTIO N IN F L OWERIN G PLANTS

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  1. SEXUALREPRODUCTIONIN FLOWERINGPLANTS

  2. Prefertilization:structureandevents: • Hormonalandstructuralchangesinplantsleadstodevelopmentofflower, • Androeciumconsistsofawhorlofstamensrepresentsmalesexorgan. • Gynoeciumrepresentsthefemalereproductiveorgan. • Stamen,MicrosporangiumandPollengrain: • Typicalstamenconsistsoftwoparts,longandslenderstalk • calledfilamentandterminalbilobedstructurecalledanther. • Atypicalangiospermantherisbilobed. • Eachlobehavetwothecai.e.dithecous. • Eachanthercontainsfourmicrosporangialocatedatthecorners,twoineachlobe. • Microsporangiabecomepollensacsandarepackedwithpollen • grains

  3. Structureofmicrosporangium: • Structureofmicrosporangium: • Eachmicrosporangiumsurroundedbyfourwalllayers • Epidermis • Endothecium • Middlelayer. • Tapetum. • Theinnermostlayeristapetumwhichismultinucleated,withdensecytoplasm;itnourishesthedevelopingpollengrain. • Thecentersofeachmicrosporangiumcontainhomogenouscellscalledsporogenoustissues.

  4. Microsporogenesis: • Theprocessofformationofmicrosporesfrompollenmothercellthroughmeiosisis • calledmicrosporogenesis. • Thesporogenoustissueofmicrosporangiumdifferentiatedintomicrosporemother • cellorpollenmothercell. • Eachmicrosporemothercellundergoesmeiosis • andgivesrisetohaploidmicrosporetetrad. • Ondehydrationmicrosporetetraddissociatedtoformfourmicrospores. • Eachmicrosporedevelopedintoapollengrain.

  5. Pollengrain: • Pollengrainrepresentsthemalegametophytes. • Itissphericalandmeasuringabout25-50micrometerindiameter. • Itiscoveredbytwolayers. • Thehardouterlayercalledtheexineismadeupofsporopollenin,whichisoneofthemostresistantorganicmaterialsknown.Itcanwithstandhightemperatureandstrongacidsandalkali.Noenzymecandegradessporopolleninissofarknown. • Theexinehasprominentaperturescalledgermporewheresporopolleninisabsent. • Theinnerwallofpollengrainiscalledintine.Itisthinandcontinuouslayer • madeofcelluloseandpectin. • Onmaturitythepollengraincontainstwocells,thevegetativecellandgenerativecell. • Thevegetativecellisbigger,hasabundantfoodreserveandalargeirregularlyshapednucleus. • Thegenerativecellissmallandfloatsinthecytoplasmofvegetativecell. • In60%ofangiosperms,pollengrainsareshedatthis2-celledstage. • Inothersthegenerativecelldividesmitoticallytoformtwomalegametesbeforepollengrainareshed(3-celledstage).

  6. Economicimportanceofpollengrain : • Pollengrainmaycausesevereallergiesandbronchialafflictions. • Itmaycausechronicrespiratorydisorders– asthma,bronchitis,etc. • PollengrainofPartheniumorcarrotgrasscausespollenallergy. • Pollengrainsarerichinnutrientshenceusedaspollentabletsforfoodsupplements. • Pollenconsumptionsincreaseperformanceofathletesandracehorses. • Aftersheddingtheviabilitydependsontemperatureand • humidity. • Inwheatandricethepollengrainloseviabilitywithin30min.oftheirrelease. • InRosaceae,LeguminoseaeandSolanaceaetheyremainviable • formonths. • Pollengraincanbepreservedforyearsinliquidnitrogen(-196oC).

  7. ThePistil,Megasporangium(ovule)andEmbryoSac: • TheGynoeciumrepresentsthefemalereproductivepartoftheflower. • TheGynoeciummaycontainsinglepistil(monocarpellary)ormayhavemorethanonepistil(multicarpellary). • Fusedpistilsarecalledsyncarpousandfreepistilsarecalledapocarpous. • Eachpistilhasthreepartsthestigma,styleandovary. • Insidetheovaryistheovariancavity(locule). • Theplacentalocatedinsidetheovariancavity. • Megasporongiaorovulesarisefromtheplacenta. • Thenumberofovuleinsidetheovarymaybesingleormany.

  8. TheMegasporangium(Ovule): • Ovuleisasmallstructureattachedtotheplacentaofloculewithastalkcalledfunicle. • Thebodyoftheovulefusedwiththefunicleinthe • regioncalledhilum. • Hilumisthejunctionbetweenthefunicleandovule. • Eachovulehasoneortwoprotectiveenvelopscalledinteguments. • Integumentcoveredtheovuleexceptanopeningatthetopcalledmicropyle. • Oppositeofthemicropylarend,isthechalaza,representingthebasalpartoftheovule?

  9. Megasporogenesis: • Theprocessofformationofmegasporesfromthemegasporemothercellis • calledMegasporogenesis. • Inthecentreoftheovulethereisamassoftissue • callednucellus. • Cellsofnucellushaveabundantreservefoodmaterials. • Onecellofthenucellustowardsmicropylarend • differentiatedintomegasporemothercell(MMC). • Itisalargediploid • cell,densecytoplasmwithprominentnucleus. • TheMMCundergomeioticdivisionresultingfour • haploidmegaspores.

  10. Femalegametophyte: • Outoffourmegaspores,onemegasporeisfunctionalandotherthreedegenerates. • Thefunctionalmegasporedevelopedintothefemale • gametophyte. • Femalegametophyteisknownastheembryosac. • Developmentofembryosacfromasinglemegasporeiscalledasmonosporictypeofembryosac. • Thenucleusofthefunctionalmegasporedividedbymitoticdivisiontoformtwonucleiwhichmovetotheoppositepole,2-nucleatedembryosac. • Twosuccessivemitoticdivisionleadstoformationof4-nucleateandlater8-nucleatestagesoftheembryosac. • Allmitoticdivisionsarefreenucleartype;karyokinesisis • notfollowedbycytokinesis.

  11. Sixoftheeightnucleiaresurroundedbycellwallsandorganizedintocells.Sixoftheeightnucleiaresurroundedbycellwallsandorganizedintocells. • Threecellsaregroupedtogetheratthemicropylarend,constitutetheeggapparatus. • Theeggapparatus,inturnconsistsoftwosynergidsand • oneeggcell. • Synergidshavespecialfiliformapparatus,whichplayanimportantroleinguidingtheentryofpollentubeintothesynergids. • Threecellsarrangedtowardschalazalendarecalledantipodalcells. • Thelargecentralcellhastwopolarnuclei. • Atypicalangiospermembryosacatmaturityis8- • nucleatedand7-celled.

  12. Pollination: • Transferofpollengrainsfromtheanthertothestigmaofapistilistermedaspollination. • Bothmaleandfemalegametesarenon-motile. • Kindsofpollination: • Autogamy: • Pollinationwithinsameflower. • Inopenandexposedanthersandstigmaautogamyisrare. • Viola,OxalisandCommelinaproducetwotypesofflowers: • Chasmogamous:exposedantherandstigma • Cleistogamous:closedantherandstigma. • Cleistogamousflowerisinvariablyautogamousandassuredseedsetevenintheabsenceofthepollinator.

  13. Geitonogamy: • Pollinationbetweentwoflowersofthesameplant. • Pollinationbypollinatingagent. • Geneticallysimilartotheautogamy. • Xenogamy: • Transferofpollengrainsfromtheanthertothe • stigmaofdifferentplant. • Itiscommonlycalledascross-pollination. • Itbringsgeneticallydifferenttypesofpollengrains • tothestigma

  14. Agentsofpollination: •  • Plantusetwoabioticagenti.e.windandwaterforpollination. • Onebioticagentforpollinationsuchasanimals. • Majorityofplantusebioticagentforpollination. • Fewplantuseabioticpollinatingagent.

  15. Anemophily: • Pollinatingagentiswind. • Plantsproducesenormousamountofpollenwhencomparedtothenumberofovulesavailableforpollinationtocompensatetheuncertaintiesofpollination. • Flowerswithwellexposedstamens. • Largefeatherystigmatotrapair-bornepollengrains. • Mostwindpollinatedflowercontainssingleovuleinoneovaryandnumerousflowerpackedintoaninflorescencee.g.corncob. • Pollengrainsarelightandnon-sticky.

  16. Hydrophilic: • Pollinationbyabioticagentlikewater. • Thistypeofpollinationisveryrare,about30genera, mostlymonocot. • Vallisneria,HydrillaandZosteraarethecommonexampleforHydrophily. • AllaquaticplantsarenotHydrophily. • PollengrainsreleasedintothesurfaceofwaterandcarriedtothestigmabyaircurrentasinVallisneria. • Inseagrasstheflowersremainedsubmerged. • Pollengrainsarelong,ribbonlikeandcarriedpassivelyinsidethewater • Pollengrainsareprotectedfromwetting bymucilaginouscovering.

  17. Pollinationbybioticagent: • Majorityoffloweringplantsusearangeofanimalsaspollinatingagents. • Amongtheanimal,insectparticularlybeesarethedominantbioticagentsforpollination. • Insectpollinatingflowersareverylarge,colorful,fragrantandrichinnectar. • Smallflowerspresentinclustertomakethemconspicuous. • Flowerpollinatedbyfliesandbeetlessecretefoulodours. • Nectarandpollengrainsaretheusualfloralrewardsforinsects. • Insomespeciesfloralrewardsareinprovidingsafeplacestolayeggs: • e.g.Amorphophallus. • AspeciesofmothandYuccaplantcannotcompletetheirlifecyclewithouteachother.Themothdepositsitseggsintheloculeoftheovaryandtheflowerinturngetpollinatedbythemoth. • Manyinsectsmayconsumepollenornectarwithoutbringaboutpollination.Suchfloralvisitorsarereferredaspollen/nectarrobbers.

  18. OutbreedingDevices: • Majorityofthefloweringplantsproducehermaphroditeflowerandundergoautogamy. • Continuousautogamyorself-pollinationresults • ininbreedingdepression. • Floweringplantshavedevelopedmanydevicestoavoidselfpollinationandtoencouragecross-pollination.SuchdevicesarecalledOutbreedingdevices. • Pollenreleasedandstigmareceptivityisnot • synchronized. • Spatialseparationofanthersandstigmas • Antherandstigmaareplacedatdifferentpositions. • Selfincompatibility. • Productionofunisexualflowers.

  19. PollenpistilInteraction: • Alltheevents– frompollendepositiononthestigmauntilpollentubesentertheovule– aretogetherreferred • aspollen-pistilinteraction. • Pollinationdoesnotguaranteethetransferoftherighttypeofpollengraintotherighttypeofstigma. • Thepistilhastheabilitytorecognizethepollenwhetheritiscompatibleorincompatible. • Ifitisrighttypethestigmaallowthepollentogerminate. • Ifitiswrongtypethestigmarejectsthepollen,preventinggermination. • TheabilityofthepistiltorecognizethepollenbycontinuousdialoguemediatedbychemicallikeBoron,Inositolandsucroselevel. • Followingcompatiblepollination,thepollengrainproduce • pollentubethroughoneofthegermpore.

  20. Artificialhybridization: • Oneofthemajorapproachesofcropimprovementprogramme. • Onlydesiredpollengrainusedfor • pollination. • Stigmaisprotectedfromcontamination(fromunwantedpollengrain). • Removalofanthersfromtheflowerbudbeforetheantherdehiscesiscalledemasculation. • Emasculatedflowerscoveredbybaggenerallymadeupofbutterpaper,topreventcontaminationofitsstigmawithunwantedpollen.Thisstepiscalledbagging. • Ifthefemaleflowerisunisexualthereisnoneedofemasculation.

  21. Doublefertilization: • Afterenteringoneofthesynergids,thepollentubereleasestwomalegametesintothecytoplasmofthesynergids. • Syngamy:oneofthemalegametefusedwitheggcell,toformadiploidzygote. • Twopolarnucleiofcentralcellfusedtoformadiploidsecondarynucleus. • Triplefusion:Thesecondmalegametefusedwiththesecondarynucleustoformatriploidprimaryendospermnucleus. • Sincetwotypeoffusion,syngamyandtriplefusiontakeplaceintheembryosacthephenomenonistermedasdoublefertilization. • Thecentralcellaftertriplefusionbecomesprimary • endospermcellanddevelopedintotheendosperm. • Thezygotedevelopedintoanembryo.

  22. POST-FERTILIZATION: STRUCTUREANDEVENTS • Eventsofendospermandembryodevelopment,maturationofovuleintoseedandovaryintofruit,arecollectivelytermedaspost-fertilizationevents. • Endosperm: • Developmentofendospermtakesplacebeforetheembryodevelopment. • Primaryendospermcelldividesrepeatedlytoformatriploidendosperm. • Cellsarefilledwithreservefoodmaterialandareusedforthenutritionofthedevelopingembryo. • PENundergoessuccessivenucleardivisiontogiverisetofreenuclei.Thisiscalled • free-nuclearendosperm. • Subsequentlycellwallformationtakesplaceandbecomecellularendosperm. • Thecoconutwaterisfreenuclearendospermandthewhitekernelisthecellularendosperm. • Endospermmaybeconsumedcompletelyduringembryodevelopedoritmaybeconsumedduringgerminationofseed.

  23. Embryo: • Zygoteformedandplacedatthemicropylarendoftheembryosac. • Zygotestartsitsdevelopmentonlyaftersomeamountofendospermformed. • Embryodevelopmenttakesplaceinfollowing • stages: • Proembryo • Globularstage • Heartshaped • Maturedembryo

  24. Dicotembryo: • Atypical • dicotyledonousembryoconsistsof • anembryonalaxisand • twocotyledons. • Embryonalaxisabovethecotyledonistheepicotyls. • Terminalpartoftheepicotylsis • theplumule(givesrisetotheshoot). • Embryonalaxisbelowthecotyledonisthehypocotyl. • Theterminalpartofthehypocotyliscalledtheradicle(roottip). • Theroottipiscoveredbytheroot • cap.

  25. Monocotembryo: • Possessesonlyonecotyledon • Ingrassfamilythecotyledoniscalledscutellum. • Scutellumsituatedtowardsonesideoftheembryonalaxis. • Radicleandtherootcapenclosedbyasheathcalledcoleorhiza. • Theportionoftheembryonalaxisabovelevelofattachment • ofscutellumiscalledepicotyls. • Epicotylhastheshootapexorplumuleenclosedbyhollowfoliarstructurecalledcoleoptile. • Seedisthefinalproductofthesexualreproduction. • Seedconsistsofseedcoat,cotyledonandanembryoaxis.

  26. Cotyledonstoresthereservefoodmaterialfordevelopmentandgermination.Cotyledonstoresthereservefoodmaterialfordevelopmentandgermination. • Maturedseedwithoutendospermcallednon-albuminous.(Groundnut) • Apartoftheendospermretainedinmaturedseed • isAlbuminous. • Remainantsofnucellusinthematuredseediscalledperisperm. • E.g.blackpeeper,beet. • Thewalloftheovarydevelopsintothewalloffruit • calledpericarp. • Fruitdevelopedfromtheovaryiscalledtruefruit. • Inapple,strawberry,cashew,thethalamuscontributesinthefruitformationiscalledfalsefruit. • FruitdevelopedwithoutfertilizationiscalledParthenocarpic • fruits.

  27. APOMIXISANDPOLYEMBRYONY. • ApomixisisverycommoninAsteraceaeandgrasses. • Seedsareproducedwithoutfertilization. • Apomixisisatypeofasexualreproductionwhich • mimicsthesexualreproduction. • Diploideggcellisformedwithoutmeiosisanddevelopsintoseedwithoutfertilization. • InCitrusandMangothenucellarcellsstartsdividing, • protrudeintotheembryosacanddevelopintoembryo. • Ovulehavingmorethanoneembryoistermedaspolyembryony. • Hybridplantsaredevelopedbyapomixistomaintain • thegeneticidentity.

  28. Thankingyou Thankingyou

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