1. AN INTRODUCTION TO THE
EMBRYOLOGY OF ANGIOSPERMS
Dr. Harwinder Kaur
Department of Botany
Akal University, Talwandi Sabo
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
• Embryology is the study of the process of formation
of embryo in a fertilized ovule, i.e., the study of the
changes taking place in an ovule before and after the
fertilization. In case of angiosperms flowers are main
reproductive units.
(a) Micro- and mega-sporogenesis in the diploid
generation
(b) Micro- and mega- gametophytes in the haploid
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
• In Angiosperms, during
the sporophytic phase
meiotic division took
place for the formation
of spores, which are
haploid.
• Production of
microspores in anther
and megaspores in the
ovary is known as
sporogenesis
GAMETOGENESIS
• The spores germinate to
give rise to haploid
gametophyte, which yield
gametes.
• Two types of gametes are
produced, their
development is called
microgametogenesis and
megagametogenesis in
anther and 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
11. A. Anther primordium
B. Archesporial layer next to
the epid.
C. Mitotic div. in archesp layer
forms primary parietal layer
(PPL)and sporogenous cells
D. Division in the PPL (see
arrow) gives rise to 2
additional layers.
E. Inner PPL differentiates
into outer Tapetum. Outer
PPL differentiates into the
sec. parietal layer.
F. Additional mitotic division
of outer PPL gives rise to
Endothecium and Middle
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
14. Meiotic divisionsI
II
A Pachytene, D. Metaphase
B. Diplotene E. Anaphase
C. diakinesis F. Telophase
(cell plate not formed
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
17. Microgametogenesis
• Microgametogenesis is the process in plant
reproduction where a microgametophyte
develops in a pollen grain to the three-celled
stage of its development. In flowering
plants it 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.
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
• Megagametogenesis is 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.
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-nucleated str. 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 4th 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
31.
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 Flies Pollination 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
• The fusion of one of the two sperms with the egg cell ,
producing a diploid zygote , is known as fertilization .
The fusion of remaining sperm with the secondary
nucleus , leading to the formation of a triploid primary
endosperm nucleus , is terms as triple fusion .
• The endosperm nucleus produces endosperm through
repeated mitotic divisions . During seed development ,
endosperm provides nutrition to developing embryo .
The endosperm may become absorbed completely ,
example – in legumes , or it may form major portion of
seed , in monocots like maize, wheat,etc., and some
dicots, e.g. castor , Brassica spp. , etc.
36. Double Fertilization
• After landing on a receptive stigma, a pollen
grain produces a pollen tube that extends
between the cells of the style toward the ovary.
• Double fertilization results from the discharge
of two sperm from the pollen tube into the
embryo sac.
• One sperm fertilizes the egg, and the other
combines with the polar nuclei, giving rise to
the triploid food-storing endosperm (3n).
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 cases where
first division of the zygote is vertical (e.g.Lornthaceae,
Piperaceae).
40.
41.
42.
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
In a strict sense, embryology is confined to a study of the
embryo, but most botanists also include it under the events which
lead on to fertilization. In this presentation, an account of the
development of the male and female gametophytes and
fertilization is provided.
Embryology of angiosperms provide important data which come
up with the solution to the problems of systematic botany like
Number, position and character of germ pore in pollen grains;
development and structure of the ovule; type of fertilization; seed
coat development; special features of apomixis and
polyembryony etc. Now-a-days experimental embryology has
been explored to produce in vitro plants through tissue culture;
anther culture, pollen culture, embryo culture.
48. REFERENCES
Bhojwani, S.S. & Bhatnagar, S.P. 2015. The embryology of Angiosperms. Vikas
publiser house, New Delhi. Pp:1-376.
Maheshwari, P. 1950. An introduction to the embryology of angiosperms. McGraw
Hill publications in the Botanical Sciences Book Company Inc., New York & London.
Johri, BM. Embryology of angiosperms.1984, Pp:1-802
http://www.biologydiscussion.com/embryology/embryo-meaning-development-
and-modes-with-diagrams-botany/20796
Robert B. Goldberg, Genaro de Paiva, Ramin Yadegari. 1994.Plant Embryogenesis:
Zygote to Seed, Vol 266. Pp: 605-614.
