Double fertilization is a unique and crucial process in flowering plants, involving two sperm cells and two female gametes, ultimately leading to both embryo and food source development.
It was discovered by Nawaschin in the liliaceous plants like Lilium and Fritillaria.
Pollen grains, carrying two male gametes, which lands on the stigma, the sticky landing pad atop the flower. After a pollen grain has reached the surface of the stigma, The pollen grain germinates, sending a microscopic tube (pollen tube) down the style, the long passage to the ovary.
Chemicals released by the ovule guide the pollen tube towards the micropyle, a tiny opening. It is termed as porogamy. But in some cases, it is found to enter through chalaza, known as chalazogamy and in some plants by piercing the integuments, called mesogamy.
The two non-motile male gametes penetrates the stigma and forms a pollen tube reaching the ovule. The watery synergid contents nourish the tube, which bursts releasing the gametes. This pollen tube-mediated delivery is siphonogamy.
Inside the ovule, one gamete fuses with the egg, forming a diploid zygote (syngamy) for embryo development.
The other fuses with two central nuclei, forming a triploid endosperm nucleus (triple fusion) for nutrient storage.
This unique two-fertilization process combines genetic diversity (syngamy) with nutritional provisioning (triple fusion) for successful seed development.
Here, both the male gametes participate and therefore, it is described as or called double fertilization.