Micro and Megasporogenesis

1. DR. DILIP V. HANDE
PROFESSOR
DEPT OF BOTANY
SHRI SHIVAJI SCIENCE COLLEGE AMRAVATI
SEM- III

2. *
Flower- A modified
shoot-
Reproductive
structure of
angiosperms
2

3. *
A typical stamen-
• the long and slender stalk
called the filament
• the terminal bilobed structure
called the anther.
• Monothecous Hibiscus,
Dithecous brinjal
The proximal end of the filament
is attached to the thalamus or the
petal of the flower.
The number and length of
stamens vary.
3

4. *
Dithecous - anther is bilobed
with each lobe having two theca
A longitudinal groove runs
lengthwise separating the theca.
4

5. * 5

6. T.S. OF AN ANTHER
6

7. *
*Dithecous - bilobed nature
*The anther is a four-sided (tetragonal) structure - four
microsporangia located at the corners, two in each lobe.
*The microsporangia develop- pollen sacs. They extend
longitudinally ,are packed with pollen grains.
*Structure of microsporangium: In T.S. a typical microsporangium
appears circular in outline. It is generally surrounded by four wall
layers -- the epidermis, endothecium, middle layers and the
tapetum.
*The outer three wall layers perform the function of protection
and help in dehiscence of anther to release the pollen.
* The innermost wall layer is the tapetum. It nourishes the
developing pollen grains. Cells of the tapetum possess dense
cytoplasm and generally have more than one nucleus. Nucleus
divides – without cytoplasmic division- polyploidy
7

8. *
*When the anther is young, a group of compactly arranged
homogenous cells -the sporogenous tissue occupies the centre
of each microsporangium.
*The cells of the sporogenous tissue undergo meiotic divisions
to form microspore tetrads. ( haploidy)
8

9. *
Potential
pollen /
Potential
microspore
mother cell
Micro-
spore
Tetrad
Pollen
grains
Cells
of
sporangeous
tissue
Four cells
Haploid
Stay together
Tetrad cells
separates
Meiosis
Micro-
sporogenesis
Anthers
mature,
Dehydration
Dissociate
9

10. 10
*
*The pollen grains represent the male
gametophytes.
*sizes, shapes, colours, designs- different
species
*fossils because of the presence of
sporopollenin
*Cryopreservation(-196 0C ) used in crop
breeding
*Pollen food nutritional value –
performance of athletes and race horses
*Pollen Allergy, bronchial
*Afflictions, asthma, bronchitis eg
Parthenium
*Viability of pollen grains depends on
temperature and humidity. Viable from
few mins to several months
*– few mins (rice) to few months
(Solanacae), Rosaceae, Leguminoseae

11. 11
*Pollen grain wall- exine and intine
*Exine – thick hard ornamental, made up of sporopollenin
( most resistant organic material high temperature, acid, alkalies)
*Germ pore- circular aperture in exine- spropollenin absent.
Pollen tube emerges from germ pore
*The inner wall of the pollen grain intine- a thin and continuous
layer made up of cellulose and pectin.

12. 12

13. 13
The cytoplasm of pollen grain is surrounded by a plasma membrane. A
mature pollen grain – ( inside intine and exine )
During development from microspore mitosis – 2 cells
• vegetative cell / tube cell --bigger, has abundant -food reserve and a
large irregularly shaped nucleus.
• generative Cell -- small , spindle shaped with dense cytoplasm & a
nucleus. It floats in the cytoplasm of the vegetative cell.
60 % angiosperms, pollen grains are shed at 2-celled stage.
In others generative cell divides mitotically - the two male gametes
before pollen grains are shed (3-celled stage).

14. 14
*
*Pistil/gynoecium innermost whorl
*Carpel – stigma , style , Ovary
*Ovary many ovule ( megasporangia) attached to a tissue
inside ovary – placenta – ovarian cavity ( locules) –
*Placentation – recap
*number of ovules in an ovary may be one (wheat,
*paddy, mango) to many (papaya, water melon, orchids).
*Monocarpellary / multicarpellary
*Syncarpous ( pistils fused together) , aopcarpous ( free)

15. 15

16. 16
*
1. Funicle The ovule is attached to the placenta by means of a stalk called
funicle.
2. Hilum The body of the ovule fuses with funicle in the region called
hilum.(hilum - the junction between ovule and funicle)
3. Integuments Each ovule has one or two protective envelopes called
integuments.(inner and outer )
4. Micropyle The integuments leave small opening at one end called micropyle.-
this end is micropylar end.
5. Chalaza Opposite the micropylar end, is the chalaza, representing the basal
part of the ovule.
6. Nucellus Tissue encloses embryo sac
7. Embryo sac
(female
gametophyte)
An ovule generally has a single embryo sac formed from a megaspore
through reduction division.
* Nucleate and 7 celled.
1. Egg apparatus- at micropylar end. It has 2 synergids and an egg.
2. Filiform apparatus- synergids – special thickening at micropylar
end. It guides the pollen tube.
3. Antipodals- 3 in number twds chalazal end.
4. Two Haploid nuclei at polar end below egg appataus

17. 17
* (1) Orthotropous : The micropyle, chalaza
and funicle are in a straight line. This is the
most primitive type of ovule e.g., Piper,
Polygonum, Cycas. - A
*(2) Anatropous : The ovule turns at
180 angle. Thus it is inverted ovule.
Micropyle lies close to hilum or at
side of hilum e.g, found in 90% of
angiosperm families. B
* (3) Campylotropous : Ovule is curved more
or less at right angle to funicle. Micropylar
end is bend down slightly e.g., in members
of Leguminosae, Cruciferae. D
* (4) Hemianatropous : Ovule turns at 90
angle upon the funicle or body of ovule and
is at right angle to the funicle e.g.,
Ranunculus. C
* (5) Amphitropous : Ovule as well as
embryo sac is curved like horse shoe e.g,
Lemna, Poppy, Alisma. E
* (6) Circinotropous : The ovule turns at
more than 360 angle, so funicle becomes
coiled around the ovule e.g., Opuntia
(Cactaceae), Plumbaginaceae. F

18. *
Megaspore
mother cells
MMC
Deploid
Megaspore
haploid
Monosporic
development
Functional
megasopre
to Embryo
sac
Cells in the
nucellus
near
micropylar
region.
Four cells
Haploid
3 near
micropyle
degenerrate
1 functional
megaspore
Meiosis
Mega-
sporogenesis
Functional megaspore enlarges,
mitotic division 2 nuclei – move
opposite poles – 2 mitoic
division- 4 nuclei at each pole
Wall formation only after this
stage
Chalaza end – 3 form antipodals
Micropylar end – 3 form egg
apparatus
Remaining 2 nucei Polar nuclei
in large central cell.
18

19. 19
*
Megaspore
mother cells
MMC
Diploid

20. 20
Functional
megaspore
to Embryo
sac
Functional megaspore enlarges, mitotic division 2
nuclei – move opposite poles – 2 mitoic division- 4
nuclei at each pole
Wall formation only after this stage
Chalaza end – 3 form antipodals
Micropylar end – 3 form egg apparatus
Remaining 2 nucei Polar nuclei in large central cell.

21. 21
*

22. 22
*
*All events from deposition of pollen grains on stigma – entry
of pollen tube into the ovule -Pollen pistil interaction
*Identification of compatible (same species) or incompatible(
other species) pollen grains by stigma
*a dynamic process involving pollen recognition followed by
promotion or inhibition of the pollen.
*Reason – chemical interaction between pollen and stigma
*Compatible pollen accepted by stigma, initiates post
pollination events

23. 23
*
*Germination- formation of pollen tube through germ
pore- content move to pollen tube- through stigma, style
reaches ovary
*pollen grains - two-celled condition (a vegetative cell
and a generate cell)- the generative cell divides and
forms the two male gametes during the growth of pollen
tube in the stigma.
*three-celled condition, pollen tubes carry the two male
gametes from the beginning.
*Pollen tube, after reaching the ovary, enters the ovule
through the micropyle and then enters one of the
synergids through the filiform apparatus
*Interaction is important in plant breeding- for superior
plant development

24. 24
*
Pollen tube into
synergid
• the pollen tube releases the two male gametes into the
cytoplasm of the synergid.
Syngamy
• the pollen tube releases the two male gametes into the
cytoplasm of the synergid.
• Diploid Zygote formation - zygote develops into an embryo.
Triple fusion
3 haploid nucleus
fuse
• other male gamete moves towards the two polar nuclei located
in the central cell and fuses with them to produce a triploid
PEN This central cell forms
• primary endosperm cell (PEC) and develops into the endosperm

25. *
1
4
2
pollen is
transferred
3
After fertilization
flower withers
seeds disperse
and germinate
into new plant
seeds develop
in ovary
4

26. 1 Male gamete fuses
with the 2 polar nuclei
to form the triploid
endosperm nucleus
1 male gamete
fuses with the egg
nucleus to form the
diploid zygote
Double fertilization recap

27. 27
*
*After double fertilization events of endosperm and embryo
development, maturation of ovule(s) into seed(s) and ovary
into fruit, are collectively termed post-fertilisation events.
➢Endosperm development
➢Embryogeny
➢Seed formation
*Endosperm development : Primary Endosperm Cell (Triple
fusion) – Endosperm (3n)
*Endosperm – cells filled with reserved food material -main
source of nutrition for the embryo

28. *
•The endosperm nucleus
(3N) divides repeatedly
to form the endosperm
in endospermic seeds.
This endosperm acts as
a food store for the
developing seed
•e.g. maize
3N
endosperm
nucleus
2N Zygote

29. 29
*
Nuclear
• PEN successive nuclear divisions free nuclei. free-
nuclear endosperm. Nuclei free, the cw formation
afterwards.
Cellular
• First and subsequent divisions followed by cw
formation
Helobial
• In between above two
• Transvrse wall mycropylar and chalazal
chamber
Non persistant embryo in some seeds,& perisperm till germination

30. 30
Embryogeny - Embryo formation – similar in Mono cot and dicot
Embryo develops micropylar end sac where the zygote is situated.
First endosperm develops then zygote. Provision of nutrition taken care
Zygote – proembryo – globular
mature heart shaped embryo
1 st
divisio
n
Transverse division – 2 cells
Cell twds micropyle
embryo/terminal cell
Other – basal cell / suspensor
cell
Suspe
nsor
cell
Transverse division, 6-10 cells
forms suspensor
Terminal cell is swollen,
vesicular Haustorium
Lowermost – hypophysis to root
tip and root cap

31. 31
Embryo cell Vertical division at right angles to one another- 4 cells
then transverse division – 8 cells (octant)
Terminal four to plumule
Towds hypophysis to hypocotyle and radical
Proembryo Undifferntiated , globular
To heart shaped- then maturity

32. Dicot embryo consists of an
embryonal axis and two
cotyledons.
The portion of embryonal axis above
the level of cotyledons is the
epicotyl, which terminates with the
plumule or stem tip.
The cylindrical portion below the
level of cotyledons is hypocotyl that
*terminates at its lower end in the
radical or root tip. The root tip is
covered with a root cap.
32
*

33. *In the grass family the cotyledon is
called scutellum - situated towards
one side (lateral) of the embryonal
axis.
* At its lower end, the embryonal axis
has the radical and root cap enclosed
in an undifferentiated sheath called
coleorrhiza.
*The portion of the embryonal axis
above the level of attachment of
scutellum is the epicotyl. Epicotyl
has a shoot apex and a few leaf
primordia enclosed in a hollow foliar
structure, the coleoptile.
33
*

34. Endosperm
Food store
for
developing
embryo
Embryo
Plumule,
radicle,
cotyledons
Integuments, becomes the seed coat
*
Micropyle – pore-entry
Of oxygen, water during
germination

35. If all the
endosperm is
absorbed by
the developing
embryo the
seed is a non
endospermic
seed e.g. broad
bean, pea,
groundnut
*

36. If all the
endosperm is
not absorbed
by the
developing
embryo the
seed is an
endospermic
seed e.g.
Maize, wheat,
barley, castor,
sunflower
*

37. e.g. Broad Bean e.g. Maize
Plumule
Radicle
Cotyledon
Endosperm
Non–endospermic and Endospermic seed

38. *
38

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After fertilization
Integuments Seed coat
Micropyle Seed pore
Ovules seed
Ovary fruit
Wall of ovary pericarp

40. 40
True fruit False fruit Parthenocarpic
Fruit develops only from
the ovary.
Floral parts - the
thalamus also
contributes to fruit
formation. apple,
strawberry, cashew
fruits develop without
fertilisation.
Banana
Refer BASE Book for
details
Induced - application of
growth hormones-
auxins
Seedless Grapes
Dormany importance drying
Advantages of seed for formation BAsE module

41. 41
Non reccurrent
Normal embryo sac
production
Haploid egg/other cell to
embryo
Sterile plants, non recurrent
Recurrent
No meiosis
Diploid nuclei in embryo
Egg/ any cell (2n)
Adenttive/Saprophytic
budding
Embryo from nucellus/
integuments
Apomixis -- seed without fertilization, grasses
Hybrid apomixis discussion

42. 42
*
*More than one embryo in the seed
1. Zygote / proembryo into 2/more units -
then in embryo
2. Embryos from other part of embryo sac than
egg say synergids ( antipodals rare)
3. Cells of nucellus integuments – mango, citrus
4. Multiple embryosac in ovule- all fertilised

43. 43