Double Fertilization in Flowering Plants

Overview

• Flowering plants exhibit a unique reproductive process called double fertilization.
• Involves two fertilization events between male and female reproductive organs.

Female Reproductive Organ: Ovule Changes

• The ovule initially contains one reproductive cell called the megaspore or mother cell (diploid).
• Undergoes meiosis to produce four haploid megaspores.
  • Three megaspores degenerate, leaving one surviving megaspore.
• The surviving megaspore undergoes three rounds of mitosis to create eight haploid nuclei.
  • These nuclei share the same cytoplasm initially.
• The resulting structure is called the embryo sac.

Formation within the Embryo Sac

• Cell walls form between most of the nuclei:
  • Three antipodal cells form opposite the micropyle.
  • Three cells form above the micropyle: two are synergids and one is the egg cell.
  • Two central nuclei remain together in a large cell.
• The egg cell and the central nucleate cell participate in double fertilization.

Male Reproductive Organ: Pollen Transfer

• Pollen grain contains:
  • Tube cell: bulk of the pollen grain.
  • Generative cell: becomes sperm cells.
• Pollen grain lands on the stigma, germinates:
  • Tube cell grows down the style into the ovary.
  • Generative cell follows behind tube nucleus, divides by mitosis forming two haploid sperm cells.

Double Fertilization Process

• Pollen tube reaches micropyle, releasing sperm cells into embryo sac.
• First sperm cell fertilizes egg cell forming a diploid zygote (embryo origin).
• Second sperm cell fuses with central nuclei creating a triploid endosperm (food supply).

Unique Feature

• Double fertilization is characteristic of angiosperms (flowering plants).
• Gymnosperms, ferns, mosses do not exhibit this process.