Fertilization, Double Fertilization

1. Name : Yasir ahmad
C.No : 64
Semester : 2nd
Department : agronomy
Assignment : 02
Subject : seed physiology
Course NO : agron 721
Submitted to : prof.dr.inamullah

2. fertilization
Fertilization is the process by which the male
gamete (sperm) from the pollen grain fuses with
the female gamete (egg cell) within the ovule to
form a zygote, which is the first cell of a new
plant. This process results in the formation of a
seed, which contains an embryo and a food
reserve tissue called endosperm. Fertilization in
plants is essential for the sexual reproduction
and propagation of the species.

4. DOUBLE FERTILIZATION
Double fertilization is a
unique process that
occurs in the
reproductive cycle of
angiosperms
(flowering plants). This
process involves the
fusion of two sperm
cells with two female
gametes to form a
diploid zygote and a
triploid endosperm.
This unique process of
double fertilization is
one of the key features
that distinguishes
angiosperms from
other plants.

5. Double fertilization
Double fertilization is a unique process that occurs in
flowering plants, and it is one of the defining features
of angiosperms. It involves the fusion of two sperm
cells from a single pollen grain with two different
female gametes within the ovule. One sperm cell fuses
with the egg cell to form a diploid zygote, while the
other sperm cell fuses with the central cell to form a
triploid endosperm. Double fertilization is essential for
the successful reproduction and propagation of
flowering plants, as it ensures that the developing
embryo has access to the energy and nutrients
required for growth and development.

6. Step1: Pollination
The process of double
fertilization begins with
pollination, which is the
transfer of pollen from the
anther of a flower to the stigma
of the same or another flower.
The anther is the male
reproductive organ that
produces and releases pollen,
while the stigma is the
receptive surface that captures
and recognizes the pollen.
Pollination can occur in
several ways, such as by wind,
water, or animal pollinators.

7. Step2: Pollen Tube Formation
Once a pollen grain lands on
the stigma, it germinates and
forms a pollen tube. The tube
grows down the style, which
is the long, narrow part of the
pistil that connects the
stigma to the ovary. The
process of pollen tube
formation is guided by
chemical signals released by
the female reproductive
tissues. The tip of the pollen
tube is highly specialized and
secretes enzymes that break
down the stigma and style
tissues, allowing the tube to
penetrate these tissues.

8. Step3: Male Gametophyte
Development
The male gametophyte
develops from the pollen grain
inside the pollen tube. The
pollen grain contains a
vegetative cell and a
generative cell. The vegetative
cell forms the pollen tube,
while the generative cell
divides to produce two sperm
cells. In most angiosperms,
the generative cell divides just
before or after the pollen grain
lands on the stigma, producing
two sperm cells that remain
attached.

9. Step 4: Entry of the Pollen Tube into the Ovule
Once the pollen tube
reaches the ovary, it
grows through the
micropyle, which is a
small opening in the
ovule's outer covering.
The pollen tube then
grows towards the
female gametophyte,
which is located inside
the ovule.

10. Step 5: Female Gametophyte Development
The female gametophyte,
also known as the
embryo sac, develops
within the ovule. The
process of female
gametophyte
development involves
the division of the
megaspore, which is a
specialized cell within
the ovule. The
megaspore undergoes
several rounds of
mitosis to form the
embryo sac, which
contains the female
gametes.

11. Step6: Fusion of Sperm andEgg
Once the pollen tube
reaches the female
gametophyte, one of the
sperm cells fuses with
the egg cell to form a
diploid zygote. The
zygote will develop into
the embryo of the plant.
The fusion of the sperm
and egg is known as
syngamy.

12. Step7: Fusion of Sperm and Central Cell
The second sperm cell
fuses with the central
cell, which contains
two polar nuclei, to
form a triploid
nucleus. This process
is known as triple
fusion. The central cell
is a specialized
structure that
develops within the
female gametophyte.
The triploid nucleus
that forms as a result
of the fusion will
develop into the
endosperm.

13. Step8: Endosperm Development
After triple fusion, the triploid
nucleus divides repeatedly to
form the endosperm, a
nutrient-rich tissue that
provides nourishment to the
developing embryo. The
endosperm is essential for
the growth and development
of the embryo, as it provides
energy, nutrients, and
hormones required for the
embryo to develop into a
mature plant. Endosperm are
divided into three main types
based on their development
pattern.

14. 1. Nuclear Endosperm
In this type of endosperm,
the nuclei divide without
cytokinesis, resulting in a
large multinucleate cell that
later undergoes
cellularization to form the
endosperm. This type of
endosperm is found in
plants like Arabidopsis
thaliana and tomato. Nuclear
endosperm is the most
common and is found in
about 56% families of
angiosperms.

15. 2. Cellular Endosperm
In this type of
endosperm, the nuclei
divide and cytokinesis
occurs, resulting in the
formation of individual
cells that make up the
endosperm. This type of
endosperm is found in
plants like maize and rice.
Cellular endosperms
occur in 25% families of
angiosperms.

16. 3. Helobial Endosperm
This type of endosperm
is found in aquatic
plants like water lilies
and consists of two
types of cells - large
peripheral cells with
dense cytoplasm and
smaller central cells
with more vacuolated
cytoplasm. The central
cells are surrounded by
the peripheral cells,
forming a double layer
of endosperm. Helobial
endosperms occur in
19% families of
angiosperms.

17. Step9: Embryo Development
After fertilization, the
zygote undergoes
several rounds of cell
division and
differentiation to form the
embryo. The embryo
develops within the ovule
and is surrounded by the
endosperm. The embryo
will develop into a
mature plant once the
seed is dispersed and
germinates under
appropriate conditions.

18. Step 10: Seed Development
The ovule that contains the
fertilized egg, endosperm,
and embryo, will develop
into a seed. The seed is a
protective structure that
encloses and protects the
developing embryo and
provides the means for the
plant to disperse and
germinate. The seed coat,
which is derived from the
integuments of the ovule,
protects the embryo from
environmental stresses and
also plays a role in seed
dormancy.

19. Conclusion
Double fertilization is a unique and complex
process that occurs in flowering plants. It
involves the fusion of two sperm cells with two
different female gametes, resulting in the
formation of a diploid zygote and a triploid
endosperm. This process is essential for the
successful reproduction and propagation of
flowering plants and ensures that the developing
embryo has access to the energy and nutrients
required for growth and development. The
process of double fertilization is highly regulated
and involves a range of interactions between the
male and female reproductive structures of the
plant.