Reproduction in lower and higher plants notes part 3

Microsporogenesis-

1. Process of formation of Microspores by meiosis from MMC- Microspore Mother Cell

2. Pollen grain- Non-motile with single nucleus.

3. Pollen wall, double layered - Sporoderm

4. Pollen wall-

• Exine (outer wall)
• Intine (inner wall)

Exine (outer wall)

• Thick
• Composed of non- biodegradable sporopollenin
• Protective layer
• Smooth or variously sculptured, spiny
• Presence of thin areas germ pores for emergence of pollen tube

Intine (inner wall)

• Thin
• Cellulose and pectin
• Forms pollen tube
• Smooth

5. Pollen Viability : It is the ability of pollen grain to germinate and develop male gametophyte.

• Depends on environment factors – Temperature and humidity.
• It lasts for few minutes (Grasses, Wheat, Rice) to months (Members of Rosaceae, Solanaceae, Fabaceae, Leguminosae)

6. Development of male gametophyte :

• It is considerably reduced.
• Develops in flower.
• Pollen grain (n) is first cell of gametophyte.

7. Pollen grain-

1. First mitotic division → 2 unequal cells →

1. Vegetative cell
2. Generative cell

Vegetative cell

• Larger, Naked
• Rich in food
• Irregular nucleus

Generative cell

• Smaller, thin walled
• Dense cytoplasm
• Floats in cytoplasm of Vegetative cell

2. Second mitotic division → In generative cell → equal cells

• Two non-motile male gametes produced
• Either occur in pollen grain or in pollen tube.

3. Pollen grains are shed in either two celled stage or three celled stage.

• Pollen grains are lodged on stigma of pistil.

Structure of Anatropous ovule (Most common type)

1. Anatropous Ovule:

Ovule are preset in ovary.

• Uniovulate – Mango, Wheat, Rice.
• Multiovulate – Tomato, Lady’s finger. 

3. Parts of ovule :

• Funiculus : Stalk by which ovule is attached to placenta.
• Hilum : Point of attachment.
• Anatropous ovule : Curved ovule, where micropyle is near stalk.
• Nucellus : Parenchymatous tissue that forms body of ovule.
• Integuments : Outer and inner two protective coverings
• Micropyle : Narrow opening at apex.
• Chalaza : Base of ovule.
• Female gametophyte or embryo sac remains embedded in nucellus.
• Oval, elongated, multicellular 7 celled structure.