Lecture Notes: Plant Development and Germination

Key Concepts

• Pollen Transfer and Fertilization

  • Completion of pollen transfer and fertilization marks the beginning of zygote and embryo development.

• Formation of the Zygote

  • Post-fertilization, a diploid zygote is formed, marking the start of the sporophyte generation.
  • Initial unequal cytokinesis results in a smaller daughter cell (embryo) and a larger daughter cell (suspensor).

• Roles of Embryo and Suspensor

  • Embryo: Develops into the future plant; most cytoplasm goes here for further division.
  • Suspensor: Provides a link to the nutrient supply; primarily vacuole-filled.

Developmental Axes

• Vertical Axis Formation
  • Established by unequal cell division.
  • The axis guides differentiation: shoot system grows upward, root system downward.
  • Influenced by sperm entry location and environmental signals (gravity, sunlight).

Apical Meristems and Tissue Systems

• Apical Meristems: Active division areas; one for upward growth, one for downward growth.
• Embryonic Tissue Systems: Protoderma, ground meristem, procambium.
  • Protoderm: Evolves into the dermal tissue (epidermis).
  • Ground Meristem: Develops into ground tissue (space filler).
  • Procambium: Transforms into vascular tissue in adults.

Embryo Growth and Structure

• Cotyledons: Initial seed leaves aiding in food utilization.
• Embryonic Tissue Differentiation: Parallel to animal germ layers.
• Embryo's Maturity: Includes development of shoot and root apical meristems.

Seed Development and Dormancy

• Seed Maturity: Formation of seed coat and fruit.
• Dormancy: Metabolic shutdown, water removal; awaiting suitable germination conditions.

Seed Germination

• Triggering Conditions: Vary by species (temperature, water, sunlight, etc.).
• Water Uptake: Essential for breaking seed dormancy.

Eudicots vs. Monocots Germination

• Eudicots:
  • Radical Emergence: Embryonic root grows downward.
  • Hypocotyl Development: Facilitates cotyledon emergence above ground.
  • Cotyledons: May or may not photosynthesize.
• Monocots:
  • Radical and Stem Protection: Sheaths (coleorhiza for radical, coleoptile for stem) protect from abrasive soil.
  • True Leaves First: Cotyledons remain enclosed.

Conclusion

• Post-germination growth leads to mature sporophyte development.
• Lifecycle completion: from zygote formation through seed maturation and germination to mature plant.