Angiosperm Reproduction

  • Flowers are the prime region for sexual reproduction in plants.
  • Let’s dive a bit into the morphological features of a flower which is technically a modified shoot.
    • Calyx: Outermost whorl comprising of sepals.
    • Corolla: Th next whorl comprises petals.
    • Androecium: The whorl which comprises the male reproductive part.
    • Gynoecium: The innermost whorl which comprises the female reproductive part.
  • Angiosperms are the most developed and advanced plants in the plant kingdom. These are the seeded plants that show double fertilization and triple fusion.
  • Male reproductive whorl: Androecium
    • It consists of a whorl of the stamen.
    • A typical stamen comprises a long filament and a bilobed structure called the anther.
    • Characteristics of another:
    • It is bilobed and comprises two lobes.
    • Each lobe has two thecae called dithecous.
    • It consists of four microsporangia two in each lobe called tetrasporangiate.
  • Structure of Anther: It comprises four different layers.
    • Epidermis:
    • Outermost
    • Protective layer
    • Endothecium:
    • Hygroscopic
    • Helps in dehiscence of anther
    • Middle Layers:
    • Short-lived (ephemeral)
    • Parenchymatous
    • Tapetum:
    • Polyploid and multinucleate
    • Innermost
    • Forms callase enzyme
    • Formation of ubisch bodies
    • Formation of sporopollenin
  • Microsporogenesis: The formation and differentiation of microspores are called microsporogenesis. Microspore mother cells divide meiotically to produce pollen tetrads.
  • Structure of pollen grain:
    • It is generally spherical.
    • 25 - 50 micrometers in diameter.
    • Two-layered structure:
    • Exine:
      • Outer wall
      • Thick
      • Consists of an organic non-biodegradable substance called sporopollenin
    • Intine:
      • Thin, continuous, soft, and elastic
      • Inner layer
      • Consists of pectin and cellulose
    • Study of pollen grains: Palynology
    • Germ pore: The places where exine is absent or present in form of a very thin layer.
    • In dicots: Tricolpate (3 germ pore)
    • In monocots: Monocolpate (1 germ pore)
    • Pre-pollination changes:
    • Unequal division leads to the formation of a small nucleus called the generative nucleus and a large irregular-shaped nucleus.
    • Emasculation → Bagging → Cross-pollination → Re-bagging
    • Filiform Apparatus is the cellular thickening at the end of synergids.