Pollination and Double Fertilization

• Pollination and double fertilization are fundamental processes in the sexual reproduction of flowering plants (angiosperms).
• Pollination is the transfer of pollen grains from the anther (male part) to the stigma (female part) of a flower, enabling fertilization and subsequent production of seeds.
• Double fertilization is a unique characteristic of angiosperms, involving two fertilization events within the ovule, resulting in the formation of both the embryo and the endosperm.

Pollination

• Pollination is the process by which pollen grains are transferred from the male reproductive organ (anther) to the female reproductive organ (stigma) of a flower, or from the male cone to the female cone in gymnosperms.
• Pollination is essential for fertilization, which leads to the production of seeds and fruits.
• Pollination can occur through various agents, including wind, water, insects, birds, and other animals.
  • Self-pollination: The transfer of pollen grains from the anther to the stigma of the same flower or another flower on the same plant.
  • Cross-pollination: The transfer of pollen grains from the anther of one flower to the stigma of a flower on a different plant of the same species.
• Agents of pollination include:
  • Wind pollination (anemophily): Common in grasses, trees, and other plants with inconspicuous flowers that produce large quantities of lightweight pollen.
  • Water pollination (hydrophily): Occurs in aquatic plants, where pollen is dispersed by water currents.
  • Insect pollination (entomophily): Common in flowering plants that attract insects with colorful petals, fragrance, and nectar.
  • Bird pollination (ornithophily): Common in plants with brightly colored, tubular flowers that produce nectar, attracting birds like hummingbirds and sunbirds.
  • Animal pollination (zoophily): Involves various animals, such as bats, rodents, and other mammals, that transfer pollen while foraging for food.

Process of Double Fertilization

• Double fertilization is a complex process unique to angiosperms (flowering plants) that involves two fertilization events within the ovule.
• It results in the formation of both the embryo and the endosperm, the latter serving as a food source for the developing embryo.
• The process begins with the arrival of a pollen grain on the stigma of a flower.
• The pollen grain germinates to form a pollen tube, which grows down through the style and into the ovary, eventually reaching the ovule.
• The ovule contains the embryo sac, which typically consists of seven cells: the egg cell, two synergid cells, three antipodal cells, and a central cell containing two polar nuclei.
• The pollen tube carries two sperm cells.
• Upon reaching the embryo sac, the pollen tube releases the two sperm cells.
• One sperm cell fertilizes the egg cell, forming a diploid zygote, which develops into the embryo.
• The other sperm cell fuses with the two polar nuclei in the central cell, forming a triploid (3n) endosperm nucleus.
• This process results in the formation of the endosperm, a nutrient-rich tissue that provides nourishment to the developing embryo.
• The ovule develops into a seed, containing the embryo and endosperm, surrounded by a protective seed coat.
• Double fertilization ensures that the endosperm develops only when fertilization has occurred, providing a nutritional advantage to the developing embryo.
• The endosperm can be consumed by the embryo during seed development or remain present in the mature seed to support germination and early seedling growth.
• Double fertilization is a key innovation in the evolution of angiosperms.
• It contributes to their reproductive success by providing a reliable mechanism for nourishing the developing embryo and ensuring efficient seed development.
• The process of double fertilization is essential for the production of viable seeds and the continuation of plant life cycles in flowering plants.