Fertilization in Flowering Plants:

• Unique and essential process in angiosperms.
• Involves fusion of male and female gametes, forming a zygote and endosperm.
• Begins with pollination and ends with seed development and fruit formation.

Entry of Pollen Tube into Ovule:

• Critical step in fertilization.
• Pollen germination and tube growth.
• Micropyle entry, penetration, and guidance by synergid cells.
• Leads to egg cell and central cell fertilization.

Double Fertilization:

• Unique to angiosperms.
• Two sperm cells from pollen fuse with different female gametophyte cells.
• Forms a diploid zygote and triploid endosperm.
• Essential for seed development.

Development of the Endosperm:

• Nourishing tissue for embryo.
• Originates from the triploid nucleus.
• Involves mitotic divisions, cellularization, and nutrient accumulation.
• Functions as a nutrient reserve for embryo growth.

Stages in Cellular Endosperm Development:

• Initiation of endosperm with a triploid nucleus.
• Mitotic divisions leading to syncytium.
• Cellularization forming individual cells.
• Cell expansion, nutrient accumulation, and maturation.
• Nutrient reservoir for embryo.

Stages in Helobial Endosperm Development:

• Triploid primary endosperm nucleus formation.
• Free nuclear divisions, forming a coenocyte.
• Cell wall formation within the coenocyte.
• Cell expansion, nutrient accumulation, and maturation.
• Nutrient reservoir for embryo.
• Fate of helobial endosperm varies among grass species.

Steps in development of Embryo in Dicot Plants:

1. Fertilization: It begins with the fusion of sperm and egg cells, forming a diploid zygote and initiating embryo development.

2. Zygote Division: The zygote divides into the terminal cell (forms most of the embryo) and the basal cell (involved in suspensor formation).

3. Suspensor Formation: The suspensor connects the embryo to maternal tissues, aiding nutrient uptake.

4. Embryo Proper: It includes the radicle (embryonic root), hypocotyl, cotyledons (usually two), and plumule (embryonic shoot).

5. Storage Reserves: Nutrient storage occurs in cotyledons or other regions, supporting seedling growth.

6. Maturation: Prepares the embryo for dormancy inside the seed.

7. Seed Coat Formation: Provides protection to the embryo.

8. Dormancy: Many dicots enter dormancy within the seed until suitable germination conditions.

9. Germination: Resumption of growth under favorable conditions.

Steps in development of Embryo in Monocot Plants:

1. Fertilization: Same as dicots, forming a zygote and initiating embryo development.

2. Zygote Division: Divides into apical cell (forms most of the embryo) and basal cell (involved in suspensor).

3. Suspensor Formation: Multicellular suspensor connects embryo to maternal tissues.

4. Embryo Proper: Includes radicle, cotyledon(s) (usually one), and plumule.

5. Storage Reserves: Nutrients accumulate in cotyledon(s) or other regions.

6. Maturation: Prepares the embryo for dormancy.

7. Seed Coat Formation: Protects the embryo.

8. Dormancy: Enter dormancy within the seed.

9. Germination: Resumption of growth under favorable conditions.

Steps in development of Seed:

1. Fertilization: Begins with pollination and double fertilization, forming a seed.

2. Ovary Enlargement: The ovary grows and develops into the fruit.

3. Seed Development: The embryo and endosperm (if present) develop within the ovule.

4. Pericarp Development: The fruit’s ovary wall undergoes changes.

5. Fruit Growth: The fruit enlarges as cells divide or expand.

6. Fruit Ripening: Complex biochemical changes alter color, texture, and flavor.

7. Dispersal: Mechanisms (wind, animals, water) distribute mature seeds.

8. Germination: Seeds sprout when conditions are favorable.

Steps in seed Germination:

1. Imbibition: Seeds absorb water, activating enzymes.

2. Activation of Enzymes: Water activates enzymes that break down stored nutrients.

3. Radicle Emergence: The embryonic root emerges first, followed by the shoot.

4. Growth of Plumule: The shoot elongates and develops into leaves and stems.

5. Cotyledon Function: In dicots, cotyledons provide nutrients until photosynthesis begins.

6. Photosynthesis: Seedling becomes self-sufficient through photosynthesis.

7. Establishment: Seedling grows into a mature plant.

Steps in development of Fruits:

1. Fertilization: Fruit development starts with ovule fertilization.

2. Ovary Enlargement: The ovary grows and becomes the fruit.

3. Seed Development: Embryo and endosperm form within the ovule.

4. Pericarp Development: The fruit’s ovary wall changes.

5. Fruit Growth: The fruit enlarges due to cell division or expansion.

6. Fruit Ripening: Biochemical changes alter color, texture, and flavor, attracting animals.

7. Dehiscence or Indehiscence: Fruits may split open or remain closed at maturity.

8. Seed Dispersal: Various mechanisms disperse seeds (wind, animals, water).

Apomixis:

1. Asexual Reproduction: Seeds produced without fertilization, resulting in genetic clones.

2. Types of Apomixis: Agamospermy, apospory, and parthenogenesis are different forms.

3. Clonal Offspring: Offspring are genetically identical to the parent plant.

4. Reproductive Advantages: Apomixis can be advantageous in specific environments.

5. Common in Some Plant Families: Found in grasses, dandelions, and certain citrus species.

6. Applications in Agriculture: Studied for crop improvement and genetic stability.

7. Seed Production: Apomixis allows for predictable seed production.

8. Genetic Diversity: Apomixis does not contribute to genetic diversity.