Fertilisation in plants

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.

Porogamy - entry through the micropyle.
Chalazogamy - entry through the Chalaza
Mesogamy - entry through the middle part or the integuments 
Steps leading to fertilization
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
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)
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.
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
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.

Dr. T. Annie Sheron
Annie Sheron
Kakatiya Government College

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 Germination of the pollen grain: Stigma function is to provide place of lodging and germination of the pollen grain after pollination. T ypes of stigmas- Wet stigmas Secrete exudates like water and other nutrients In the form of droplets on the stigma. E xudates 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. 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. 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. 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.