NCERT · Class 12 · Biology · Sexual Reproduction in Flowering PlantsDescribe the process of double fertilization in angiosperms with a neat sequential explanation of syngamy and triple fusion. What is the ultimate fate of the products formed during this process?

Introduction to Double Fertilization\nDouble fertilization is a unique and characteristic event occurring in flowering plants (angiosperms). It was discovered by S.G. Nawaschin in Lilium and Fritillaria. It involves two distinct fusion events occurring inside the embryo sac simultaneously.

Process of Pollen Tube Entry and Discharge\nAfter a pollen grain lands on a compatible stigma, it germinates to form a pollen tube that grows through the style and enters the ovule, usually through the micropyle. The pollen tube enters one of the synergids and discharges two male gametes into its cytoplasm.

Syngamy (First Fertilization)

• One of the male gametes moves towards the egg cell and fuses with its nucleus.
• This process of fusion between a male gamete and an egg cell is called syngamy.
• The result of syngamy is the formation of a diploid zygote ($2n$).
• The zygote subsequently develops into the embryo.

Triple Fusion (Second Fertilization)

• The second male gamete moves towards the central cell and fuses with the two polar nuclei located there.
• Since this fusion involves three haploid nuclei (one male gamete and two polar nuclei), it is termed triple fusion.
• The result is the formation of a triploid ($3n$) primary endosperm nucleus (PEN).
• The central cell becomes the primary endosperm cell (PEC) and develops into the endosperm, which provides nourishment to the developing embryo.

Significance and Fate of Products

• Zygote develops into the plant embryo.
• Primary Endosperm Nucleus (PEN) develops into the nutritive endosperm tissue.
• Ovules mature into seeds, and the ovary ripens into the fruit.