Slide 1

• Topic: Reproduction in Flowering Plants - Development of Male Gametophyte
• Introduction to sexual reproduction in flowering plants
• Importance of male gametophyte development

Slide 2

• Stamen - the male reproductive organ in flowering plants
• Structure of stamen
  • Anther: Produces pollen grains
  • Filament: Supports the anther

Slide 3

• Development of male gametophyte occurs within the anther
• Anther consists of four pollen sacs that contain pollen mother cells (PMCs)
• PMCs undergo meiosis to form haploid microspores

Slide 4

• Process of microspore formation:
  1. Microspore mother cell (MMC) undergoes meiosis I.
  2. Meiosis I produces two haploid cells, each with 1n chromosomes.
  3. These cells are called dyads.
  4. Each dyad undergoes meiosis II to produce a total of four haploid microspores.

Slide 5

• Microspores are released into the anther locule
• Each microspore undergoes mitosis to produce a two-celled structure called a pollen grain
• Two cells within the pollen grain:
  • Tube cell: Gives rise to the pollen tube
  • Generative cell: Divides to form sperm cells

Slide 6

• Development of generative cell:
  1. Generative cell undergoes mitosis to produce two haploid sperm cells.
  2. These sperm cells are immotile and have a small size.

Slide 7

• Development of pollen grain:
  1. The cytoplasm of the microspore divides unequally to form a larger vegetative cell and a smaller generative cell.
  2. The cytoplasm of the generative cell separates into two haploid sperm cells.

Slide 8

• Structure of a mature pollen grain:
  • Exine: Outer layer composed of sporopollenin
  • Intine: Inner layer made of cellulose and pectin
  • Aperture: A small opening in the exine from which the pollen tube emerges

Slide 9

• Release of pollen grains from the anther
• Dehiscence: The process of anther opening to release the pollen grains
• Various modes of dehiscence:
  • Porous dehiscence
  • Longitudinal dehiscence
  • Transverse dehiscence

Slide 10

• Pollination: The transfer of pollen grains from anther to stigma
• Agents of pollination:
  • Abiotic agents (such as wind and water)
  • Biotic agents (such as insects, birds, and mammals)
• Types of pollination:
  • Self-pollination
  • Cross-pollination

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Slide 11

• Pollination mechanisms:
  • Wind pollination:
    • Flowers small, inconspicuous, and lack nectar
    • Enormous amounts of pollen produced
    • Examples: Grasses, corn, wheat
  • Insect pollination:
    • Flowers colorful, sweet-smelling, and produce nectar
    • Pollen grains are sticky or spiny
    • Examples: Roses, lilies, sunflowers

Slide 12

• Pollen-pistil interaction during pollination:
  • Pollination occurs when pollen grains land on the stigma of a compatible flower.
  • Germination of pollen grain on the stigma
  • Formation of the pollen tube through the style
  • Entry of two sperm cells into the embryo sac

Slide 13

• Germination of pollen grain:
  • Pollen grain absorbs moisture and swells
  • Pollen tube emerges through the exine aperture
  • Tube nucleus and generative nucleus move down the pollen tube

Slide 14

• Pollen tube growth and guidance:
  • Tip of the pollen tube secretes enzymes to penetrate the stigma and style
  • Chemical signals guide the pollen tube towards the ovule
  • Secretion of growth-promoting substances by the ovule

Slide 15

• Double fertilization:
  • Two sperm cells are discharged into the embryo sac
  • One sperm cell fertilizes the egg cell (syngamy)
  • The other sperm cell combines with the polar nuclei to form the endosperm (triple fusion)

Slide 16

• Syngamy:
  • Fertilization of egg cell by sperm cell
  • Formation of a diploid zygote (2n)
  • Zygote develops into an embryo

Slide 17

• Triple fusion:
  • Fertilization of the central cell’s two polar nuclei by a sperm cell
  • Formation of a triploid primary endosperm nucleus (3n)
  • Primary endosperm nucleus develops into endosperm tissue

Slide 18

• Development of the embryo:
  • Zygote undergoes embryogenesis to form a multicellular embryo
  • Formation of the suspensor: Provides nutrients to the developing embryo
  • Formation of embryonic axis: Gives rise to shoot and root systems

Slide 19

• Development of endosperm:
  • Primary endosperm nucleus undergoes mitosis to form endosperm cells
  • Endosperm provides nourishment to the developing embryo
  • Examples: Coconut water, corn kernel

Slide 20

• Summary:
  • Male gametophyte development occurs in the anther.
  • Pollen grains are released from the anther through dehiscence.
  • Pollination involves the transfer of pollen grains to the stigma.
  • Pollen grains germinate on the stigma and form a pollen tube.
  • Double fertilization results in the formation of both embryo and endosperm.

Slide 21

• Pollen grain germination:
  • Pollen tube grows towards the ovule
  • Chemical signals attract the pollen tube towards the micropyle
  • Tip of the pollen tube secretes enzymes to penetrate the micropyle

Slide 22

• Factors affecting pollination:
  • Availability of pollen and stigma receptivity
  • Environmental factors (temperature, humidity, light, etc.)
  • Structural adaptations in flowers
  • Synchrony of reproductive development between pollinators and flowers

Slide 23

• Mechanisms to prevent self-pollination:
  • Herkogamy: Physical separation of anther and stigma
  • Dichogamy: Temporal separation of anther and stigma maturation
  • Self-incompatibility: Recognition and rejection of self-pollen

Slide 24

• Advantages of cross-pollination:
  • Enhances genetic diversity
  • Increases chances of successful reproduction
  • Allows for greater adaptation to changing environments
  • Promotes the elimination of harmful genetic mutations

Slide 25

• Development of the pollen tube:
  • Pollen tube grows through the style towards the ovule
  • The tube nucleus and the generative nucleus move down the pollen tube
  • The tube nucleus degenerates before reaching the ovule

Slide 26

• Ovule development:
  1. Ovule starts as a small outgrowth from the placenta of the ovary.
  2. It differentiates into the integuments (protective layers) and the nucellus (the central mass).
  3. The nucellus gives rise to the female gametophyte or embryo sac.

Slide 27

• Structure of the ovule:
  • Micropyle: Small opening through which the pollen tube enters
  • Integuments: Protective layers around the nucellus
  • Megaspore mother cell: Develops into the embryo sac
  • Antipodal cells: Three cells at the opposite end of the embryo sac

Slide 28

• Development of female gametophyte (embryo sac):
  1. Megaspore mother cell undergoes meiosis to produce four haploid megaspores.
  2. Three of the megaspores degenerate, and the remaining one undergoes mitosis.
  3. Mitotic divisions produce seven cells with eight nuclei.

Slide 29

• Structure of mature embryo sac:
  • Egg apparatus: Consists of the egg cell and two synergids (guide pollen tube)
  • Central cell: Contains two polar nuclei (involved in triple fusion)
  • Antipodal cells: Three cells at the opposite end of the embryo sac
  • Vacuole: Fills up the central region of the embryo sac

Slide 30

• Summary:
  • Pollen grain germinates on the stigma and forms a pollen tube.
  • Various factors affect pollination, including availability of pollen and stigma receptivity.
  • Mechanisms to prevent self-pollination include herkogamy, dichogamy, and self-incompatibility.
  • Cross-pollination advantages include genetic diversity and adaptation to changing environments.
  • Ovule development leads to the formation of the female gametophyte or embryo sac.