The Slides contains are Female Reproductive part of Flower (Carpels/Pistils), Structure of Ovule, Types of Ovules, Microsporogenesis, Megasporogenesis, Structure of Pollen Grain, Structure of Embryo Sac

1. Sexual Reproduction in
Flowering Plants
Part - II
Presented by:
ShashankTripathi

2. Female reproductive part of Flower: The Pistils
• The Gynoecium represents the female
reproductive part of the flower.
• Gynoecium may consist of a single
Carpel (Monocarpellary) or may have
more than one carpel (Multicarpellary).
• If there are more than one carpels, we
use term Pistil at the place of Carpel.
• If, there are more than one carpels if they
may be fused together (syncarpous) or
free (apocarpous)

3. Female reproductive part of Flower: The Pistils
• Each Pistil has following 3 parts:
An ovary (where the ovules are
produced;),
a style (a tube on top of the ovary), and
a stigma (which receives the pollen
during fertilization).

4. Structure of a Megasporangium (Ovule):
• An Ovule has following Parts:
o Funiculus: It is the stalk to which the body of ovule is
attached with the Placenta.
o Integument: Each ovule has one or two protective
envelopes called integuments.
o Nucellus: The integument encloses a large
parenchymatous tissue known as nucellus. This is the
central part of an ovule, that encloses embryo sac.
o Micropyle: There is a small opening at the apex of the
integument called the micropyle.
o Chalaza: This is the basal part of ovule found opposite
to the micropyle.
o Embryo Sac: In center of the nucellus is situated the
female gametophyte known as embryo-sac which
develops from a functional megaspore.

5. Types of Megasporangium (Ovule):
• 1. Orthotropous or atropous ovule (ortho-
straight, tropous - turn): The body of the ovule is
erect or straight. The hilum, chalaza and the
micropyle lie in a straight line e.g. Polygonum.
• 2. Anatropous ovule (ana - backward or up,
tropous - turn): The body of the ovule becomes
completely inverted during the development, so, that
the micropyle lies very close to the hilum (e.g.,)
Gamopetalae members.
• 3. Hemi-anatropous or hemitropous ovule: The
body of the ovule is placed transversely at right
angles to the funicle. The micropyle and chalaza lie
in one straight line e.g. Ranunculus.

6. Types of Megasporangium (Ovule) Contd…:
• 4. Campylotropous ovule (kampylos -
curved): The body of the ovule is curved or
bent round so that the micropyle and chalaza
do not lie in the same straight line. e.g.
Leguminosae.
• 5. Amphitropous ovule: The curvature of the
ovule is very much pronounced and the
embryo sac also becomes curved e.g.
Allismaceae and Butomaceae.
• 6. Circinotropous ovule: The nucellus and
the axis are in the same line in the beginning
but due to rapid growth on one side, the ovule
becomes anatropous. The curvature continues
further and the micropyle again points
upwards (e.g.) Opuntia.

7. Gametogenesis in Flowering Plants:
• In flowering Plants Gametogenesis takes
place in two stages:
oSporogenesis
oGametogenesis
Gametogenesis
In Male Plants
Microsporogenesis
Microgametogenesis
In Female Plants
Megasporogenesis
Megagametogenesis

8. Microsporogenesis:
• The formation of microspores inside the microsporangia (or
pollen sacs) of seed plants from Microsporocytes or PMCs.
• Cells of the sporogenous tissues of Anther are capable to give
rise a Pollen Tetrad i.e., cluster of 4 pollens. So, they are called
as Pollen Mother Cells (PMCs).
• The nuclei of these Pollen Mother Cells undergoes Meiosis to
form a Cluster of 4 Nuclei. These clusters of nuclei are called
Pollen Tetrads as soon as they develop a cell wall around them.
• The arrangement of pollen grain in a tetrad is affected by
cytokinesis during meiosis. It is of following types:
Simultaneous type, Where, cytokinesis occurs only at the
end of meiosis II. This results in the production of four
cells by cell wall formation between the four nuclei.
Successive type, where, cytokinesis occurs twice – once at
the end of meiosis I, forming two cells and then again at the
end of meiosis II to form four cells.

9. Arrangement of Pollens in Pollen Tetrads:
• In different species the arrangement of Pollens in a
tetrads may be different.
• It can be-
Linear- E.g.,
T-Shaped- E.g.,
Decussate- E.g.,
Isobilateral- E.g.,
Tetrahedral-E.g.,
• Pollen tetrads of most of the plants are tetrahedral
in arrangement.
• As the anthers mature and dehydrate, the
microspores dissociate from each other and develop
into pollen grains.
• Inside each microsporangium several thousands of
microspores or pollen grains are formed that are
released with the dehiscence of anther.

10. Dehiscence of Anther and Release of Pollen Grains:
• It consists of the following stages:
 Expansion of the epidermis and endothecium
cells and deposition of U‐shaped wall
thickenings inside the latter.
 Enzymatic opening of the septum between
two locules.
 Mechanical rupture of the tapetum.
 Mechanical opening of the stomium by the
centripetal force of the highly turgescent
epidermis and endothecium.
 Outward bending of the locule walls by the
centrifugal force of the dehydrating epidermis
and endothecium.

11. How a Pollen looks like??
• Pollen grains are generally
spherical.
• Architecture, i.e., sizes, shapes,
colors, designs of Pollens varies
species to species.
• They are about 25-50
micrometers in diameter.

12. How a Pollen looks like??
• A pollen is provided with two coats:
Exine or Extine- It is outer tough,
cutinized layer called exine or extine. The
exine is often sculptured or provided with
spines, warts, etc.
› Exine is made up of Sporopollenin which
is highly resistant to temperature and acids
and alkalis.
Intine- The inner wall of the pollen grain
is called the intine. It is a thin and
continuous layer made up of cellulose and
pectin.
• The cytoplasm of pollen grain is
surrounded by a plasma membrane.

13. How a Pollen looks like??
• When the pollen grain is mature it contains two
cells-
 Vegetative Cell
Generative Cell
• The vegetative cell is bigger, has abundant food
reserve and a large irregularly shaped nucleus.
• The generative cell is small and floats in the
cytoplasm of the vegetative cell.
• It is spindle shaped with dense cytoplasm and a
nucleus.

14. Microgametogensis :
• Formation of gametes in the flowering plants take place inside the Pollen
grain.
• It takes place by the Mitotic division in Generative cells
• In over 60 per cent of angiosperms, pollen grains are shed at this 2-celled
stage.
• In such plants the generative cells divide mitotically after shading on the
stigma of the flower and become 3-celled in which two cells are male
gametes while third one is vegetative cell.
• In the remaining species, the generative cell divides mitotically to give
rise to the two male gametes before pollen grains are shed (3-celled
stage).

15. Megasporogenesis:
• Megasporogenesis is formation of megaspore
that is female gametophyte from the MMC.
• In the case of Angiosperms it is known as
Embryo sac.
• Megasporogenesis take place inside the ovule.
• During the Megasporogenesis one hypodermal
cell of the nucellus becomes differentiated from
the other by its bigger size, dense cytoplasm and
conspicuous nucleus, called archesporial cell.
• The archesporial cell functions as Megaspore
mother cell (MMC).
• The megaspore mother cell is diploid (2n),
which undergoes meiosis I and then Meiosis II
forms four haploid (n) megaspores

16. Megasporogenesis:
• These Megaspore tetrads are arranged in a linearly one above other.
• Unlike Microsporogenesis, Megaspore tetrads are mostly linear in arrangement
of Megaspores.
• Among these 4 Megaspore tetrads 3 gets degenerated and only one remain
functional.
• The functional megaspore gets nutrition from nucellus and enlarges to serve as
the function of female gametophyte.
• This type of embryo sac development is very common in angiosperms and is
known as ordinary type or normal type or Polygonum type embryo sac
development.
• This type is also known as monosporic type, because, out of four megaspores,
only one remains functional and forms the embryo sac.

17. Megagametogenesis:
• So, inside the female gametophyte there
is a single nucleus that undergoes a
mitotic division to give rise 2 nuclei.
• Among these two on emigrate to
chalazal end and one towards micropylar
end.
• Again both the nuclei divides
successively to give rise 4-4 cells at both
the ends.
• From these cells on from each ends
migrates towards center again and fuses
with each other, to give rise polar nuclei
or central cell.

18. Megagametogenesis:
• There is a characteristic distribution of the cells
within the embryo sac.
• Three cells are grouped together at the micropylar end
and constitute the egg apparatus. The egg apparatus,
in turn, consists of two synergids and one egg cell.
• The synergids have special cellular thickenings at the
micropylar tip called filiform apparatus, which play
an important role in guiding the pollen tubes into the
synergid.
• Three cells are at the chalazal end and are called the
antipodals.
• The large central cell, as mentioned earlier, has two
polar nuclei.
• Thus, a typical angiosperm embryo sac, at maturity,
though 8-nucleate is 7-celled.

19. Thank You!!!!