Lecture on Flower Reproduction and Plant Breeding

Introduction to Flowers

• Flowers provide pleasure with their variety of shapes and colors.
• Used to brighten homes, gardens, and city streets.
• Flowers are the reproductive organs of plants.
• Scientists breed flowers to create new, valuable plant varieties.

Flower Structure and Reproduction

General Structure

• Flowers have three sepal, three petals, and six stamens.
• Stamens produce pollen.
  • Each stamen is attached by a filament.
  • Enlarged sack at tip: anther.
  • Inside anther: four microsporangia.
  • Microsporangium nourished by tetum (layer of surrounding cells).

Formation of Pollen Grains

• Diploid sparite cells in microsporangium undergo meiosis.
• Creates four haploid microspore cells (tetrad).
• Kos layer replaced by sporopollenin.
• Microspore nucleus divides by mitosis forming a pollen grain.
• Pollen accumulates nutrient reserves and enters resting state.
• Anther releases pollen when mature and dry through endothecium.

Female Reproductive Parts

• Center of flower: three fused carpels with stigma and style.
• Base of carpel: ovary with small megasporangium.
• Ovule formation:
  • Diploid sparite cell divides to form four haploid megaspore cells.
  • Results in forming embryo sac (female gametophyte).

Pollination Process

• Transfer of pollen to stigma is pollination.
• Can occur by wind, insects, or animals.
• Pollen grain absorbs water, swells, and forms a pollen tube.
• Pollen tube contains tube nucleus and generative cell.
• Generative cell divides to form two sperm cells.

Fertilization

• Pollen tube reaches ovules via canal.
• Penetrates megasporangium releasing sperm.
  • One sperm fertilizes egg cell (zygote).
  • Second sperm fuses with polar nuclei (primary endosperm cell).

Post-Fertilization Development

• Ovary contains many ovules, each requiring fertilization.
• Style supports numerous pollen tube growths.
• After fertilization, flower parts wither, ovary remains.
• Two fertilized cells in ovule:
  • Primary endosperm divides, forms tissue.
  • Zygote divides to form basal and apical cells.

Seed and Fruit Formation

• Embryo receives nutrients, forms seed leaf (cotyledon).
• Seed coat forms from integuments.
• Ovary transforms into a fruit.
• Fruit releases seeds which germinate to form new plants.

Diversity and Importance of Flowering Plants

• Flowers facilitate efficient reproduction.
• Wide variety of flowering plants across diverse environments.
• Human breeding has developed many plants for food.
• Flowering plants contribute to a colorful world.