INTRODUCTION TO REPRODUCTIVE BIOLOGY OF ANGIOSPERMS 1.pdf

This presentation offers the basic idea about the reproductive biology of angiosperms in plant kingdom.

1. 

2. ReproductiveBiologyisthebranchofsciencesdealswiththedifferent
aspectsofthereproductiveissuesoforganismsingeneralandsexual
reproductioninparticularinthelightofmorphological,cytological&
embryologicalattributes.Sexualreproductioninvolvesaseriesofchanges
likepreparationofsexorgans(Gonads),formationofhaploidgametes,
unionofgametesasfertilization,postzygoticchangesandpostembryonic
changesmakingpassagetogiveoffspringwithvariation.Inplants,itis
mediatedbyalternationofgenerationsviamicrosporogenesis,
megasporogenesis,pollination,fertilizationanddevelopmentofmature
embryo.ThisfundamentalprocessofreproductionisDNAreplication.In
otherwords,ifanorganismwantstocontinueitsspecies,thentheyneedto
transfertheirtraitstothenextgenerationbyDNA(geneticinformation)
copyingwhichoccursduringtheprocessofreproduction.Weknow
asexuallyreproducingorganismscopytheirDNAanddividethemselves
intonewcellswhicharetheirclones.

3. Sincetheprocessofreplicationisnotcompletelyreliable,thereare
chancesofvariation,buttheyarequitelimited.Organismsneedtoadapt
themselvestothechangingenvironment;thecreationofvariantsneedsto
behastenedforthisreason.Thiswillonlyhappenwhenthereisaunionof
twodifferentDNAs.Thishighlightsthesignificanceofsexual
reproductioninorganisms.Iftworeproducingcellssimplyjoin,the
chromosomenumberintheneworganismwillbedoubled.Butthiscannot
happenbecausethenumberofchromosomesineachcellofeveryorganism
isfixed–thesameholdsgoodforthereproducingcell.Thus,the
reproducingcellsfrombothparentsreducetheirchromosomenumberinto
thehalfbeforefusionandarecalledgametes(germcells).Insimple
organisms,thesizeandshapeofgametesarealmostthesame.Butin
higherorganisms,amalegameteissmallandmobilewhilefemalegamete
islarge,immobileandtheystorefoodforthefetus.Thegametesare
producedinaspecializedsystemcalledthereproductivesystem.

5. The following basic steps are involved----
The transformation of the vegetative phase into reproductive phase by the
induction of flower through a series of changes leading to the development
of flower,
Microsporogenesis in stamen to form haploid poille4n grains-the 1
st
cell of
the male gametophyte and the megasporogenesis to form the megaspore as
the 1
st
cell of the female gametophyte,
Pollination:Eitherbyselfpollination(autogamyorGeitonogamy)orcross
pollination,Pollenreachesthestigmaofaflower.
Germination:Pollengerminatesandformsapollentubethatreachesthe
ovary,andthehaploidmalegameteisreleasedintotheembryosacby
differentembryologicalprocesses.
Theovulebythistimegetreadyforthedevelopmentofembryosac
comprisingofegg,secondaryapparatus&others
Fusion:Malegametefuseswithfemalegameteandformszygote.
Post-zygoticchangesleadtotheformationofembryo,seedformationtakes
place,babyplantsderived---alternationofgenerationcomestoanend.

7. Asweenterthe21styearofthejournalSexualPlantReproduction,itseems
bothfittingandappropriatetoconsiderthegenesisbothofthisjournalandits
parentorganization,theInternationalAssociationforSexualPlant
ReproductionResearch(IASPRR)—particularlythroughitsmuchlonger
historyofplantsexualreproductioncongresses,informalinteractionsandthis
areaofscientificpursuitasitistransformedinthemodernera.Thescienceof
sexualplantreproductionhasalonghistorythatreachesbeyondthe315years
intervalsinceCamerariusuncoveredthesexualityofplants(ŽárskýandTupý
1995),passing150yearsofneglectbeforethediscoveryofgametes,andthena
greatperiodofexplorationinthe1800sconcludingwiththediscoveryof
doublefertilizationin1898byNawashin.FromTheophrastus,
Herodotus,Leewenhoek,Grew,Camerrius,Kolreuterdifferentplantscientists
haveenrichedthisdomain.GiovanniBattitaAmici(1824)madesignificant
contributionbydiscoveringthepollentubewhilestudyingthestigmaof
Portulacaoleracea.Hesplittedopenthepollentubeandenteredthetissueof
stigma.

8. Theformationofembryoinplantsastheonsetoflifewasaverycrucial
questionandthedilemmawasabouttheoriginoftheembryo.William
Hofmeisterfirstdemonstratedthatineverycase,theembryooriginated
frompre-existingcellintheembryosacandnotfromthepollentubeon
thebasisoftheobservationsof38speciesbelongingto19generaof
angiosperms.Thisobservationsendedarigidcontroversybetween
Schlidenandhisopponents.Theexperimentalresearchalongwithits
properdocumentationoftheoriginofembryoanditsnatureoforigin
becomecrystalcleartothebiologistsafterthisepochmakingresearchand
thismadeanewavenueoftheunderstandingaboutthesexualreproduction
ofthehigherplants.Hofmeisteriswidelycreditedwithdiscoveryof
alternationofgenerationsasageneralprincipleinplantlife.Hisproposal
thatalternationbetweenaspore-bearinggeneration(sporophyte)anda
gamete-bearinggeneration(gametophyte)constitutedaunifyingtheoryof
plantevolutionthatwaspublishedin1851.

9. EduardStrasburger,directoroftheBotanyInstituteandtheBotanical
GardenattheUniversityofBonnfrom1881to1912,wasoneofthemost
admirablescientistsinthefieldofplantbiology,notjustasthefounderof
modernplantcellbiologybutinadditionasanexcellentteacherwho
stronglybelievedin"educationthroughscience."Hecontributedtoplant
cellbiologybydiscoveringthediscretestagesofkaryokinesisand
cytokinesisinalgaeandhigherplants,describingcytoplasmicstreamingin
differentsystems,andreportingonthegrowthofthepollentubeintothe
embryosacandguidanceofthetubebysynergides.Strasburgerraised
manyproblemswhicharehotspotsinrecentplantcellbiology,e.g.,
structureandfunctionofthePlasmodesmatainrelationtophloemloading
(Strasburgercells)andsignaling,mechanismsofcellplateformation,
vesicletraffickingasabasisformostimportantdevelopmentalprocesses,
andsignalingrelatedtofertilization.Demonstratedthewidespread
occurrenceofthebinucleateconditionofpollengrainsandworkedoutthe
organisationoftheembryosacofPolygonumdivaricutum.

10. HeAlsopointedoutthatthenucelluslyingclosetotheapexoftheembryo
sacbecomerichlyprotoplasmicanddividetoformsmallgroupsofcells
whichprojectintothecavityoftheembryosacandgrowintoembryoon
thebasisoftheontogenystudyofcitrusaurantium.
Discoveredsyngamy,developmentofembryosacfrommegasporemother
cellsandpointedoutmodificationofsynergidsintheprocessof
fertilisation.
StrasburgerwastheauthoroftheimportantbookUeberZellbildungund
Zelltheilung(1875),andaninfluentialLehrbuchderBotanikfuer
Hochschulen(1894,1967
29
;TextbookofBotany,1898,1965
7
).Underhis
direction,thebotanicalinstitutebecameaworldcenterforresearchin
botanyandespeciallyinthenewlyemergingscienceofcellbiology.
Strasburger'searlyresearchdealtwiththeembryologyofliverworts,ferns,
andconifers.Herecognizedthehomologyofthearchegoniaofthefern
withtheembryosacofconifers.

11. Doublefertilizationisacharacteristicfeatureofangiosperms.Syngamy
causestheformationofembryo,wherethemaleandfemalegametesfuse.
Alongwiththatthesecondarypolarnucleifusewithmalegametetoform
triploidendosperm.Itprovidesthefunctionofnourishment.
Navashin'sembryologicalresearchledhimtotheimportantdiscoveryin
1898ofdoublefertilizationinangiosperms.Observingfertilizationinthe
Turk's-caplily(Liliummartagon)andFritillariatenella,hewasthefirstto
notethatthisprocessinvolvesnotonebuttwosperm,whichforminthe
pollentube.InastudyofLiliummartagonandFrititlariatenella.showed
thatinangiospermbothmalegameteareconcernedinfertilization,on
fusingwiththeegg(syngamy)andtheotherwiththetwopolarnuclei
(triplefusion).InthestudyofLiliumsp,heobservedthatmalegameteon
fusingwitheggassyngamyandothermalegametewithtwopolarnuclei
astriplefusion.Doublefertilizationasuniversaloccurrenceof
angiosperms.Exploredanewbreezeinthedevelopmentalbiologyof
angiosperms.

12. PanchananMaheswariwasaneminentIndianbotanistandhewasknownfor
hisdiscoveryinthetechniqueoftest-tubefertilizationofangiosperms.
-Testtubefertilizationorinvitrofertilizationisatypeofprocessinvolving
fertilizationwheretheeggisfusedwiththespermoutsidei.e.inaglassortest
tube.Thewholeprocessismonitoredasthefertilizedeggisdevelopedintoan
embryo.Cultivationofplanttissueandotherorgansonanartificialmediaina
testtubeisinvitrotechnique.P.MaheshwariwhoservedasProfessorand
HeadoftheDepartmentofBotany,UniversityofDelhifrom1950to1966
builtaflourishingschoolofembryologywhichbecameinternationally
recognized.Hiscolleaguesandstudentshavecontributedsignificantlytoall
areasofembryologythroughintegrativeapproaches.Inmemoryofhisbirth
centenaryyear,wehavepreparedthisarticlethatsummarizestheworkdoneby
hisstudentsandtracesthephenomenaladvancesmadeinsomeareasinthe
post-Maheshwariera.FatherofIndianEmbryology,famousfortesttube
fertilizationofangiospermsbytissueculturemethods.Wroteanimportant
bookon“EmbryologyofAngiosperms”alongwithanumberofcontributions
inappliedandExperimentalplantembryology.Thevaluablecontributionsare
availablewiththegeneralikePaeonia,Trapa,Butomus,Peganum,Parasssiaetc
&familieslikeCrassulaceae,Liliaceae,Loranthaceae,Lemnaceae,Cyperaceae
etc.

13. Duringthe20
th
century,significantadvanceshavebeenmadein
developmentalandcomparativeembryologyanditsroleintaxonomic
considerations.Howerver,thecausesofthevariationsinspindle
organizationduringmicrosporogenesis,pollenstructureinCyperaceaeand
Epacridaceae,pollenbuddevelopmentinsomemembersofRubiaceae,
pollenembryosacinexperimentalembryologyaresomeoftheworks.
◦ W.A.Jensen
Orchidisthemostimportantepiphytesanditisworthytobepraisedbythe
beautyloversduetoitsshowy&bizarrelyshapedstructure.Itbelongsto
themostdevelopedfamily,Orchidaceaeanditencompasses6-11%ofthe
seedplants.StartsintheOrchidembryology.Healsocontributedalotin
Capsellaembryogenesis,thecentralcellplaysanimportantroleinthe
doublefertilisation.Therelationshiptothecentralcelltotheothercellsof
thematuremegagemetophyteanditspossibleroleinembryogenesiswas
discussedbyW.A.Jenseninthepaperentitled”CapsellaEmbryogenesis:
Thecentralcell”.

14. HeslopHarrisonwasaneminentEnglishprofessorofbotanywhowas
basedinNewcastleinthemiddleyearsofthetwentiethcenturyandwho
siredamini-dynastyofothereminentbiologists.HewasaFellowofthe
RoyalSocietyaswasoneofhissons;averyunusualoccurrence.
Geneticallyworkonplantsonwildroses&Willows,Rosehybrid&Salix
hybrid,LighteffectonthepupaeofButterfly.
AnumberofIndianscientistslikeSwamy,Maheswari,johri,Vasil,shivana
&othershavecontributedalottoenrichthissubject.
Ifyouhavethepassion,youcanadoalotbyyourresearch&innovative
mind.

16. 1.Googleforimages,
2.Differentwebsitestoexp0loretheidea,
3.AnIntroductiontoembryology-P.Maheswari
4.Plantanatomy7embryology-Pandey&Chakdah
5.AtextbookofBotany-B.P.Pandey
6.Theembryologyofangiosperms-S.S.Bhojwani,
7.TheEmbryologyofangiosperms-Bhojwani,Bhatnagar&Dantu
Disclaimer:Thispresentationhasbeenmadetoenrichopensourceof
knowledgewithoutanyfinancialpleasure.