The document discusses fertilization in plants, detailing the process of double fertilization where two male gametes participate in forming a zygote and an endosperm. It explains various types of fertilization based on pollen tube entry into the ovule and outlines the step-by-step events leading to fertilization, including pollen germination, pollen tube movement, and the roles of synergids. Additionally, it covers concepts like polyspermy and heterofertilization, emphasizing the genetic differences between the endosperm and embryo.

1. KAKATIYA GOVERNMENT COLLEGE, HANAMKONDA
WARANGAL(URBAN) DIST. TELANGANA STATE
DEPARTMENT OF BOTANY
Prepared by
Dr. T. Annie Sheron
Assistant Professor of Botany
FERTILIZATION IN PLANTS

2. Plant fertilization is the union of male and female gametes (reproductive cells) to produce a zygote
(fertilized egg)
Plant fertilization is the union of male and female gametes
(reproductive cells) to produce a zygote (fertilized egg)
Double Fertilization
→Both the male gametes/sperms
participate in sexual reproduction.
→ Two male gametes fuse with one
female gamete wherein one male gamete
fertilizes the egg to form a zygote, whereas
the other fuses with two polar nuclei to
form an endosperm
Triple fusion is the fusion of the male gamete with two polar
nuclei inside the embryo sac of the angiosperm.

3. https://courses.lumenlearning.com/wm-biology2/chapter/double-fertilization/
Step wise events in Double Fertilization

4. Types of Fertilization (based on the path pollen tube entry into the ovule)
→ Porogamy - entry through the
micropyle.
→ Chalazogamy - entry through the
Chalaza
→ Mesogamy - entry through the
middle part or the integuments

5. steps leading to fertilization
Steps leading to fertilization
1. Germination of the pollen grain:
Stigma function is to provide place of lodging and germination
of the pollen grain after pollination.
Types of stigmas-
Wet stigmas
→Secrete exudates like water and other nutrients
→ In the form of droplets on the stigma.
→ Exudates made up of a mix of water, lipids, sugars,
amino acids, phenolic compounds.
→ Highly viscous and adhesive. Ex: Petunia, Zea etc.
Dry stigma
→ Do not secrete exudates Ex: Gossypium

6.  Germination of pollen may occur immediately or make take few
days/weeks.
 Exine imbibes water and swells up & Intine develop into pollen
tube and comes out of germpore.
• Monosiphnous - Campanulaceae, Cucurbitaceae, Malvaceae
• Polysiphnous - Althea rosea, Malva neglecta
• Branched - Asclepiadaceae and Orchidaceae
• Masses of pollinia – Grouped pollen
Many pollen tubes germinate simultaneously
Amentiferae, the pollen tube is
 Pollen tube carries two male gametes.

7. 2. Movement of pollen tube in the style:
‒ Pollen tube reaches the style through
stigmatic papillae.
 Solid/ closed tip of the pollen tube
secretes hydrolyzing enzymes-
pectinases. Ex: Dicots
 Hollow/open Monocots
 semi-solid /half closed
‒ Contents of pollen grains reaches the pollen
tube tip (Cap block)
‒ Unidirectional - enters through the
micropyle
‒ Entry into the embryosac - through filifrom
apparatus

8. 3. Pollen tube in the synergids:
‒ Entry only through micropyle. Guided by oburator
‒ Presence of chemotropic substances
‒ Collapse of one the synergids prior to entry of the pollen
tube.
‒ Discharge of pollen tube contents
(two male gametes, vegetative
nucleus and cytoplasm) into the
synergids.
‒ Disorganization of tube nucleus

9. 4. Double Fertilization & Triple Fusion:
‒ Both the male gametes are involved in
the fertilization.
‒ Fertilize two different components of the
embryo sac - Double Fertilization
‒ One fuses with the egg nucleus
(syngamy) -> Zygote(2n)
‒ second fuses with polar nuclei ->
primary endosperm nucleus (PEN).
‒ Involves fusion of three nuclei - Triple
fusion -> Endosperm(3n)

10. Polyspermy &Heterofertilization
Heterofertilization - Type of double fertilization in plants in
which endosperm and embryo are genetically different.
This happens when two different sperm nuclei from two
different pollen tubes happen to enter the same embryo sac.