Apospory , Apogamy and Adventive Embryony

This presentation explains the unusual pathways of forming embryos of higher plants in general and apospory, apogamy, and adventive embryony in particular. It also offers the basic idea of the sexual reproduction of plants and its difference with apospory. It also highlights the importance of these vegetative methods of reproduction in crop improvement in general and horticultural plants in particular

1. REPRODUCTIVE BIOLOGY
Apospory,Apomixes & Polyembryony
By
Dr. N.Sannigrahi, Associate Professor of Botany,
Nistarini College, D .B. Road, Purulia(W.B) India

2. AMPHIMIXIS AND APOMIXIS
Duringnormalfertilization,fusionofmaleandfemalegametesleadtotheformation3
rd
cell,zygote.
Thezygotethroughpost-zygoticchangesleadstotheformationofembryo,
Thepostembryonicdevelopmentleadstotheformationofseedanditsdifferentdesiredpartstoactas
babyplantafterthegerminationinpresenceofdesirablefactorsd,.
Thenormalprocessofsexualreproductionneedsmeiosisandmitosisatsubsequentintervals,
Thehaploid(n)anddiploid(2n)phaseregularlyalternateeachotherknownasalternationof
generationsi.e.sporophytetogametophyteandgametophytetosporophyte.Thisisthetruefeaturesof
amphimixis.
However,thenormalprocessofsexualreproductionissubstitutedbyanasexualprocess.
Thephenomenonofsubstitutionofsexualprocessbyasexualmethodsinknownasapomixisandthe
plantsshowthephenomenoniscalledapomicticplants.
Thedifferenttypeofapomixistakesplaceincropplantsasfollows.

3. MODE OF PLANT REPRODUCTION
Reproduction is one of the most important life processes and plants are not beyond its exception.
The mode of reproduction of mainly crop plants may be broadly grouped into three categories-
•A.VEGETATIVEORASEXUAL-Thevegetativep[artoftheplantsactaspropaguleinplaceof
seed.
Thefollowingorganscanbeassociatedwiththistypeofreproduction
Modifiedstem-Rhizome(Ginger,turmeric),tuber(Potato),Bulb(Onion,garlic),Corn(
Colocasia,Yam),stolon(strawberry),sucker(Chrysanthemum,Mentha)etc.
Stemcutting-Sugarcane,mango,litchi,lemon,grapes,
Normalormodifiedroot-Normalrootsofwoodapple,citrusandmanysuchtreesalongwith
modifiedrootsincaseofsweetpotato,fasciculaterootasindahlia,asparagus.
Bulbils-Globosebulbcanbeusedasmultiplicationunit.
B.APOMIXIS-Nonormalembryodevelopment,embryomaydevelopfromunfertilizedeggcellor
otherthaneggcell
C.SEXUAL-Amphimixiswheretheembryodevelopsfromthefertilizationofnormaleggwithmale
gameteleadingtothedevelopmentofzygoteandpost-zygoticchangestoembryo.

4. APOMIXIS
•Innormalsexualcycle(amphimixis),diploidsporophyticcell(MegasporeMotherCell)ofovule
transformstohaploidgametophyticcells(embryosac)throughmeiosiswhichcontaineggcell
thatformsembryoafterfertilizationwithmalegamete(syngamy).Butinsomeplantsmeiotic
divisionandsyngamyareeliminatedandstillaviableembryoisformedinsidetheovule.The
formationofembryowithasexualmeansiscalledapomixis(Apo=awayfrom+mixis=actof
mixing)andseediscalledapomicticseed.
•Thusapomixisreferstosubstitutionoftheusualsexualreproductionbyaformofasexual
reproductionwhichdoesnotinvolvemeiosisandsyngamyforembryoformation(Bhojwaniand
Bhatnagar1999).
•Polyembryonyisatypeofapomixeswhichinitiatesautonomousdevelopmentofembryos
throughasexualmodeandtheresultingprogeniesarethegeneticreplicasofthemotherplant.
Polyembryonyinplantsoccursasfacultativeapomixiswhereinsimultaneousgrowthofmultiple
embryosofsomaticoriginco-existinthesameseedcontainingsexualembryoresultingfromself
orcrosspollination.Polyembryonyisexhibitedbyanumberofplants,yetlittleisknownabout
theoriginofthisreproductivecycle.

5. APOMIXIS
Apomixisoftwotypes-ApomicticEmbryoSacandApomicticEmbryo
ApomicticEmbryoSac-Aposporyoftwotypes-
HaploidAposporyi.eembryosacdevelopsfromhaploidmegaspore
DiploidApospory-Embryosacdevelopsfromnucellusorothercells
•ApomicticEmbryo-
Androgamy–Theembryodevelopfrommalegamete,
Apogamy-OthercellsoftheEmbryosacexcepteggcelldevelopembryo,
Parthenogenesis-Developmentofembryowithoutfertilization
A.Haploid-Eggcell(unfertilized)developshaploidembryo,
B.Diploid-Diploidembryodevelopsfromdiploidcell

6. APOMIXIS
•CHARACTERS:
I.ThereisnofertilizationbetweeneggandmaleGamete,
II.Nodevelopmentofembryo,
III.However,embryomaydevelopfromunfertilizedeggwithintheembryosacfromthecelloutsidethe
embryosac,
IV.Theapomixisareoftwotypes-obligatethatonlyproduceapomicticembryoandfacultative
producingbothapomicticandnormalembryos,
V.Thephenomenonwherethesubstitutionofsexualprocessoccursbyasexualprocessisknownas
apomixisandtheplantsarecalledapomicticplants.
VI.Apomixisoftwotypes-Non-recurrentandRecurrent

7. NON-RECURRENT APOMIXIS
Here,theseed/plantdevelopsfromunfertilizedeggcelloranyotherunfertilizedhaplodcellofthe
embryosac,
Theeventofnormalsexualprocessoccursgivingtheformationofnormalembryosacxbut
fertilizationdoesnottakeplaceduetothefollowingreasons-
Absenceofpollentube,
Inabilityofthetubetodischargeitscontents,
Noattractionbetweenmaleandfemalegamete,
Earlydegenerationofthemalegametenuclei,
Maturationofthemalegameteandtheeggwithoutdesiredsynchronizationforfertilization.
Itmayleadthetwofates-
•Haploidparthenogenesis-Here,thehaploid(n)embryodevelopsfromanunfertilizedeggcellofthe
embryossaclikeOrchismaculata,Cephalantheradamasonium.
•HaploidApogamy-AnyothercelloutsidetheembryosacmayformhaploidembryobasinLilium
maratagon,Erythraeacentarium–twopro-embryosdevelop,onefromfertilizedeggandanother
fromsynergidcell.

8. RECURRENT APOMIXIS
Here, the meiotic event does not take place either in somatic cell or the meiocyte cell fails to undergo
meiosis, thereby produces the embryo sac with diploid cell only.
Thediploidcellsdirectlygiverisetodiploidembryocalledapospory.
Theaposporymaybetwotypes-
GenerativeApospory-Thediploideggcelldevelopsintoembryowithoutfertilizationasexhibitonly
inPartheniumargenatum,
SomaticApospory-Thediploid(2n)cellofnucellusorintegumentdevelopsdirectlyintodiploid
embryosacandthediploidembryoisdevelopedfromtheunfertilizedeggcellasfoundinAllium,
Meliss,Crepisetc.
AGAMOSPORY
Plantsthathaveseedhabitforpropagationbutnotthroughnormalsexualcycle,
Theembryosmaydevelopfromthediploidsporophyticcelloftheovulesuchasnucellusor
integuments,
Diplospory,aposporyandadventivesembryony–allareincludedinthisgroup.

9. AGAMOSPORY
•CHARACTERS:
Theplantswhichhasseedhabitpropagationbutnotthroughcompletenormalsexualcycle,either
meiosisorsyngamyorbothareeliminated,
Thisincludestheembryoswhichmaydevelopfromcelloftheunreducedfemalegametophyteor
directlyfromthediploidsporophytic(2n)celloftheovulesuchasnucellusorinteguments(outeror
inner),
Diplospory,aposporyandadventiveembryony–allareincludedwithinthiscategory.
•DIPLOSPORY
Here,theMMC(MegasporeMotherCell)differentiatesintosexualovules,butitdoesnotenterinto
meiosis,
Itproducestheembryosdirectlybymitoticdivision,
Allthecellswithintheembryosacarediploidandtheembryosareformedfromthosecells.

10. ADVENTIVE EMBRYONY
Here,thegametophyticgenerationiscompletelyeliminated,
Itisveymuchclosetovegetativepropagation,\Theplantshereretainedtheseedhabit,
Thediploidembryoisdevelopedfromanydiploidcelloutsidetheembryosacbutmaturesinto
embryowithintheembryosac,Zygoticembryosdegeneratesorcompeteswithapomicticembryos,
Thiskindofembryosarefoundincitrus,mangoandmanyotherangiospermplants.

11. POLYEMBRYONY
•Polyembryonyisatypeofapomixiswhereinautonomousdevelopmentofsupernumerary
embryostakesplaceintheseedandconsequentlygeneticallysimilarprogeniesaredeveloped.
Supernumeraryembryosareproducedindifferentfrequenciessinglet,duplet,triplet,quadruplet,
quintuplet,sextupletandsoon.
•Amongdifferenttypesofpolyembryony,nucellarembryonic(2n)isthemostcommon.However
formationofmultipleembryosfromcleavageofpro-embryoshasalsobeenobservedinsome
plantspecies.
•Thedegreeofpolyembryonyisinfluencedbypollensourceandenvironmentalfactors;howeverit
iscontrolledbyadominantgenehavingheterozygousallele(Pp).Morphologicallyzygotic
embryosareusuallylargerthantheotherembryos;howevermorphologicalidentificationof
nuclearseedlingsispracticallydifficultduetotheavailabilityofveryfewmorphologicalmarkers.
Ontheotherhand,biochemicalandmolecularmarkersarereliabletoolstodistinguishzygotic
andnucellarseedlings

12. POLYEMBRYONY RESEARCH
•PolyembryonywasfirstreportedbyLeeuwenhoekincitrusasearlyas1719andthedifferent
casesofpolyembryonywerestudiedbyBraunin1859.
•In1878Strasburgerdemonstratedtheformationofpluralembryosinmanygeneraof
angiosperms.
•In1901,Earnstsummarizedtheworksdoneinpolyembryonyandclassifiedthevariousmeansby
whichadventitiousembryosarederived.
•FollowingErnst’swork,itsoonbecameapparentthatpolyembryonyisnotanabnormalfeature,
whichitwasconsideredearlier,butratheradesirablecharacter.About255generabelongingto
153familiesarereportedtoexhibitpolyembryony(Carman1997).

13. POLYEMBRYONY -TYPES

14. POLYEMBRYONY
•Polyembryonyisofbroadlyoftwotypes-
A.TRUEPOLYEMBRYONY -Whenthemanyembryosaredevelopedinthesameembryosac,itis
calledtruepolyembryony.
B.FALSEPOLYEMBRYONY -Whenmorethanoneembryosdevelopintheembryosacinsidethe
ovule,itiscalledfalsepolyembryony.
•Polyembryonymaydevelopseedsbyoneofthefollowingmethods.
1.CLEAVAGEPOLYEMBRYONY -Whenmorethanoneembryodevelopbythecleavageofzygote,
itiscalledcleavagepolyembryony.Thisiscommonlyfoundingymnosperms.Inangiosperms,itis
foundinNymphetadvena,Nicotianarustica,Erythroniumamericanumetc.
2.EmbryofromtheotherembryosacintheovuleasfoundinCitrussp.
3.Embryofromnucellusi.e.AdventivesEmbryosdevelopfromthecellsofnucelluswhichpenetrate
theembryosacasfoundinMangiferaindicaofAnacardiaceae.
4.EmbryofromendospermasfoundinBalanophorasp.OfBalanophoraceae.
5.EmbryosfromsynergidsasfoundinSagittariasp.OfAlismataceae.
6.EmbryosfromantipodalcellsasfoundinUlmusamericanaofUilmaceae.

15. IMPORTANCE OF POLYEMBRYONY
Polyembryonyhavegreatdegreeofimportanceinhorticultureandplantbreeding,
Nucellerembryosaresupposedtobefreefromthediseases,
Propagationoffruittreeslikecitrus,mangocanbefacilitatedbythisprocess,
Theapplicationofadventiveembryonyisveryimportantfortheproductionofgeneticallyuniform
seedlingsoffruittrees,
Itcanbeusedforthedevelopmentofhomozygousdiploid,
Artificialproductionoftheseembryosfromtheeggsorsynergids.

16. THANKS TO VISIT THE PAGE
•REFERENCES:
•Google for images,
•Different WebPages for the study material.
•A Textbook of Palynology-Bhattacharya, Majumder and Bhattacharya
•Plant Breeding and Biometry-Kar and Halder,
•A text Book of Botany (Vol. II)-Hait, Bhattacharya & Ghosh
•Disclaimer:ThisPPThasbeendesignedforacademicpurposes.Theauthordoesnotclaimanykind
offinancialinterestinthisregard.Itisanendeavortoreachtheunreachedacademicfraternity.