An introduction to embryology of angiosperms

plant embryology in brief,

1. AN INTRODUCTION TO THE
EMBRYOLOGY OF ANGIOSPERMS
Dr.HarwinderKaur
DepartmentofBotany
AkalUniversity,TalwandiSabo

2. CONTENTS
•Introduction
•History
•Development of anther
•Anther wall layers
•Microsporogenesis & Microgametogenesis
•Male germ unit
•Megasporogenesis & Megagametogenesis
•Types embryo sacs
•Pollination
•Fertilization
•Endosperm development
•Seed development

3. INTRODUCTION
•Embryologyisthestudyoftheprocessofformation
ofembryoinafertilizedovule,i.e.,thestudyofthe
changestakingplaceinanovulebeforeandafterthe
fertilization.Incaseofangiospermsflowersaremain
reproductiveunits.
(a)Micro-andmega-sporogenesisinthediploid
generation
(b)Micro-andmega-gametophytesinthehaploid
generation
(c) The embryo and endosperm in the new sporophyte.

4. HISTORY
G. B. Amici (1824)
Wilhelm Hofmeister (1849)
Eduard Strasburger (1884)
Sergius Nawaschin (1898)
Panchanan Maheshwari (1963)
W.A. Jensen (1965-1975)
J. Heslop –Harrison (1986)
B.M. Johri (2015)

5. SPOROGENESIS
•InAngiosperms,during
thesporophyticphase
meioticdivisiontook
placefortheformation
ofspores,whichare
haploid.
•Production of
microspores in anther
and megaspores in the
ovary is known as
sporogenesis
GAMETOGENESIS
•Thesporesgerminateto
giverisetohaploid
gametophyte,whichyield
gametes.
•Twotypesofgametesare
produced, their
developmentiscalled
microgametogenesisand
megagametogenesisin
antherand ovary,
respectively

6. Androecium-collective
name for all stamens
In a flower.
Anther-for pollen
development
Filament-support, nutrient
transport , pollen dispersal
Wind-pollinated species-
filaments forms a flexible
swivel joint, causes anther
to flutter and shake out
pollen
Longitudinal section view
of a cherry flower

7. Stamen initiation
and emergence
diagrams
The cellular events of stamen initiation
involves -
•contributions from hypodermal layer in
some .
•with accompanying anticlinal activity
from protoderm and a little from outer
corpus.
A.Before emergence periclinal div. of corpus cells at stamen site.
B.An emergent stamen. Periclinal div of corpus cells but not the hypdermis.
C.Tangential div. of emergent stamen.
D.Emergent stamen with recent anticlinal div. of hypodermal cells and anticlinal and
periclinal div of corpus. E. adjacent section in hypodermal cells, F. predominance of
anticnal div. in hypodermis-derived cells.
corpus
hypodermal

8. Development of anther
protoderm
Hypoderm-found beneath protoderm and
becomes archesporial layer. Divides into:
1. Primary parietal cells
(outer)-differentiates into sporangial. outer
wall---endothecium and tapetum.
2. Primary sporogenous cells-
microsporocytes.
Sporangium
initiation is
restricted to four
separated areas
corresponding to
corners of the
developing anthers
hypoderm
microsporocytes

10. Magnified T. S. of one of the anther sporangium

11. A.Antherprimordium
B.Archesporiallayernextto
theepid.
C.Mitoticdiv.inarchesplayer
formsprimaryparietallayer
(PPL)andsporogenouscells
D.DivisioninthePPL(see
arrow)givesriseto2
additionallayers.
E.InnerPPLdifferentiates
intoouterTapetum.Outer
PPLdifferentiatesintothe
sec.parietallayer.
F.Additionalmitoticdivision
ofouterPPLgivesriseto
EndotheciumandMiddle
layer.
Anther wall layers

12. Glandular or secretory tapetum-
cells remain in their
the sac and later disintegrate and
absorbed by pollen
mother cells
Amoeboid or invasive
tapetum.
Flows amoeba-like into the sac
interior after callose dissolves
and engulfs the separated
microspores

13. TAPETUM

14. Meiotic divisionsI
II
A Pachytene, D. Metaphase
B. Diplotene E. Anaphase
C. diakinesis F. Telophase
(cell plate not formed
yet)
A.Late interphase in the dyad
B.Metaphase II E.tetrads
C.Anaphase II F. Post meiotic
D.Telophase II microspore
E
F
E
E
D
B
F
DC
C

15. Meiotic divisions in the microsporangium

16. Pollen grains

17. Microgametogenesis
•Microgametogenesisis the process in plant
reproduction where a microgametophyte
develops in a pollen grain to the three-celled
stage of its development. Inflowering
plantsit occurs with a microspore mother cell
inside the anther of the plant.

18. A.Microspore
B.Post-mitotic pollen grain with vegetative cell and
newly-formed generative cell.
C. Large central vacuole and generative cell appressed
to wall
V.CG.C Vacuole
G.C
.appressed
to wall

19. D. Pollen grain and generative cell have enlarged.
E. Generative cell in mitosis
F. Binucleate generative cell appressed to pollen wall

20. G. Two sperm cells still attached to each other but free from
pollen wall; pollen engorging but central vacuole
still present.
H. Mature engorged pollen grain with separated lenticular
sperm cells embedded in vegetative cell.

21. Male germ Unit
Computer-generated
three-dimensional
reconstruction of the
male germ unit
of rye (Secale cereale)
based upon serial
ultrathin sections.

22. Microsporogenesis-
formation of spores
called microspores
Microgametogenesis-
development of
microspore into the
microgametophyte or
the pollen grain
containing sperm cells

23. MEGASPOROGENESIS
•It is the formation of megaspores
•Megaspores are formed inside the ovule of seed
plants .
•A diploid cell in ovule called megasporocyte
•Megaspore mother cell undergoes meiosis and give
rise to 4 haploid megaspores
•In most plants only one of the megaspore develop
into megagametophyte & other 3 disintegrates .

24. Megagametogenesis
•Megagametogenesisis the development
of a megaspore into an embryo sac, which
is the gametophyte -though a highly
reduced one -stage in the life cycle of
vascular plants.

25. megasporogenesis
megagametogenesis

26. Types of embryo sac
Monosporic embryo sac
Polygonum Type: the embryo sac is formed by the chalazal
megaspore of the tetrad and is eight nucleate . The mature embryo
sac comprises a 3-celled egg apparatus , three antipodal cells and a
binucleate central cell.
Oenothera type: This type of embryo sac is derived from the
micropylar megaspore of the tetrad and is four nucleate. The
organisation of mature embryo sac is; an egg apparatus and is
uninucleate central cell.

27. BIOSPORIC EMBRYO SAC
Allium type: The embryo sac is derived from the
chalazal dyad cell.
Endymion type: The embryo sac is formed by the
micropylar dyad cell.

28. Adoxa type: The embryo sac is eight nucleate, formed after a single
post-meiotic mitosis, and its organisation is similar to polygonum
type.
Penaea type: as a result of two post-meiotic mitosis in the
coenomegaspore (16-nucleated).
Plumbago type: one post meiotic mitosis (8-nucleatedstr. Formed)
Mature embryo sac comprises:-1 egg cell, 4-nucleate central cell &
3-nuclei as peripheral cell.
Tetrasporic embryo sac

29. Peperomia type: Embryo sac is 16-nucleate.the organisation
of mature embryo sac is an egg apparatus comprising an egg
and only one synergid, six peripheral cells & a central cell
with 8 polar nuclei.
Drusa type: This type embryo sac is 16 nucleate. The mature
embryo sac comprises a normal egg apparatus(3-celled), two
polar nuclei , & 11 antipodal cells.
Tetrasporic embryo sac

30. After second meiosis, 3 megaspore nuclei fuse to form 3N nucleus
at CE and 4
th
nucleus N at the mature embryo.
Fritillaria type: 1+3 arrangement of megaspores, 4 Div. occur.
Plumbagella type:1+3 arrangement of megaspores, 3 Div. occur .
Tetrasporic embryo sac

32. Pollination
•In angiosperms, pollination is the transfer of
pollen from an anther to a stigma.
•Pollination can be by wind, water, or animals.
•Types: Self & Cross Pollination
•Anemophilly,Hydrophilly
•Entomophilly, Orinthophilly, Myrmecophilly,
Chiropterophilly, Malacophilly

33. Abiotic Pollination by Wind Pollination by Bees
Hazel staminate flowers
(stamens only)
Hazel carpellate
flower (carpels only)
Common dandelion
under normal light
Common dandelion
under ultraviolet light

34. Pollination by Moths
and Butterflies
Blowfly on carrion
flower
Pollination by FliesPollination by Bats
Moth on yucca flower
Long-nosed bat feeding
on cactus flower at night
Hummingbird
drinking nectar of
columbine flower
Pollination by Birds
Stigma
Anther
Moth
Fly egg

35. Fertilization
•Thefusionofoneofthetwospermswiththeeggcell,
producingadiploidzygote,isknownasfertilization.
Thefusionofremainingspermwiththesecondary
nucleus,leadingtotheformationofatriploidprimary
endospermnucleus,istermsastriplefusion.
•Theendospermnucleusproducesendospermthrough
repeatedmitoticdivisions.Duringseeddevelopment,
endospermprovidesnutritiontodevelopingembryo.
Theendospermmaybecomeabsorbedcompletely,
example–inlegumes,oritmayformmajorportionof
seed,inmonocotslikemaize,wheat,etc.,andsome
dicots,e.g.castor,Brassicaspp.,etc.

36. Double Fertilization
•Afterlandingonareceptivestigma,apollen
grainproducesapollentubethatextends
betweenthecellsofthestyletowardtheovary.
•Doublefertilizationresultsfromthedischarge
oftwospermfromthepollentubeintothe
embryosac.
•Onespermfertilizestheegg,andtheother
combineswiththepolarnuclei,givingriseto
thetriploidfood-storingendosperm(3n).

37. Stigma
Pollen
tube
2 31
2 sperm
Style
Ovary
Ovule
Micropyle
Pollen
grain
Polar
nuclei
Egg
Ovule
Polar
nuclei
Egg
Synergid
2 sperm
Endosperm
nucleus (3n)
(2 polar nuclei
plus sperm)
Zygote
(2n)

38. Ovule
Endosperm
nucleus
Integuments
Zygote
Zygote
Terminal cell
Basal cell
Proembryo
Suspensor
Basal
cell
Cotyledons
Shoot
apex
Root
apex
Suspensor
Seed
coat
Endosperm

39. Embryogeny in dicotyledons Acc. To classification of Johansen 1950
A.The apical cell of the 2-celled proembryo divides
longitudinally.
(1)The basal cell plays only a minor role or none in the
subsequent development of the embryo proper.(e.g.
Brassicaceae, Onagraceae,Ranunculaceae).
(2)The basal cell and apical cell both contribute to the
development of embryo.(e.g.Asteraceae,Vitaceae,
Violaceae).
B.The apical cell of the 2-celled proembryo divides
transversly. The basal cell plays only a minor or none in
the subsquent development of the embryo proper.
(3)The basal cell usually forms a suspensor.( e.g.
Linaceae,Solanaceae,Theaceae).
(4)The basal cell undergoes no further div.,& the
suspensor ,if present is always derived from the apical
cell.(e.g.Caryophyllaceae,Crassulaceae).
(5)The basal and apical cells both contribute to the
development of
embryo.(e.g.Boraginaceae,Chenopodiaceae).
(6) Johansen (1950) reported sixth type of embryogeny,
called Piperad type which includes those caseswhere
first division of the zygoteis vertical (e.g.Lornthaceae,
Piperaceae).

43. Endosperm Development
•Endosperm development usually precedes
embryo development.
•In most monocots and some eudicots,
endosperm stores nutrients that can be used
by the seedling.
•In other eudicots, the food reserves of the
endosperm are exported to the cotyledons.

44. Embryo Development
•The first mitotic division of the zygote splits
the fertilized egg into a basal cell and a
terminal cell
•The basal cell produces a multicellular
suspensor, which anchors the embryo to the
parent plant
•The terminal cell gives rise to most of the
embryo
•The cotyledons form and the embryo
elongates

45. Seed Development, Form, and
Function
•After double fertilization, each ovule develops
into a seed.
•The ovary develops into a fruit enclosing the
seed(s).

46. Figure 38.8
Seed coat
Radicle
Epicotyl
Hypocotyl
Cotyledons
(a) Common garden bean, a eudicot with thick cotyledons
(b) Castor bean, a eudicot with thin cotyledons
(c) Maize, a monocot
Seed coat
Endosperm
Cotyledons
Epicotyl
Hypocotyl
Radicle
Radicle
Hypocotyl
Epicotyl
Endosperm
Pericarp fused
with seed coat
Scutellum
(cotyledon)
Coleoptile
Coleorhiza

47. CONCLUSION
Inastrictsense,embryologyisconfinedtoastudyofthe
embryo,butmostbotanistsalsoincludeitundertheeventswhich
leadontofertilization.Inthispresentation,anaccountofthe
developmentofthemaleandfemalegametophytesand
fertilizationisprovided.
Embryologyofangiospermsprovideimportantdatawhichcome
upwiththesolutiontotheproblemsofsystematicbotanylike
Number,positionandcharacterofgermporeinpollengrains;
developmentandstructureoftheovule;typeoffertilization;seed
coatdevelopment;specialfeaturesofapomixisand
polyembryonyetc.Now-a-daysexperimentalembryologyhas
beenexploredtoproduceinvitroplantsthroughtissueculture;
antherculture,pollenculture,embryoculture.

48. REFERENCES
Bhojwani,S.S.&Bhatnagar,S.P.2015.TheembryologyofAngiosperms.Vikas
publiserhouse,NewDelhi.Pp:1-376.
Maheshwari,P.1950.Anintroductiontotheembryologyofangiosperms.McGraw
HillpublicationsintheBotanicalSciencesBookCompanyInc.,NewYork&London.
Johri,BM.Embryologyofangiosperms.1984,Pp:1-802
http://www.biologydiscussion.com/embryology/embryo-meaning-development-
and-modes-with-diagrams-botany/20796
RobertB.Goldberg,GenarodePaiva,RaminYadegari.1994.PlantEmbryogenesis:
ZygotetoSeed,Vol266.Pp:605-614.