What is double fertilisation? Describe the process in brief.
Double fertilization is a major characteristic of flowering plants. In this process, two male gametes fuse with one female gamete wherein one male gamete fertilizes the egg to form a zygote, whereas the other fuses with two polar nuclei to form endosperm.
Double fertilization gives stimulus to the plant that results in the development of the ovary into fruit and ovules into seed. The fusion of haploid male and female gametes restores the diploid condition of the plant.
Process of double fertilisation:
- After successful pollination, the pollen grain germinates on the stigma to form the pollen tube.
- The pollen tube carries in the cytoplasm two male gametes and one tube nucleus into the ovary.
- The pollen tube enters the ovary mostly through the micropyle region, near the egg apparatus. This movement is guided by the filiform apparatus.
- Inside the ovary, the pollen tube absorbs water and bursts open, releasing the two male gametes and the tube nucleus.
- The tube nucleus degenerates, and the two male gametes prepare for fusion.
- One of the male gamete fuses with the egg cell to form the diploid zygote.
- The other male gamete fuses with the diploid secondary nucleus to form the primary endosperm nucleus (PEN).
- The zygote develops to form the new plant, while the PEN develops to form the endosperm, which provides nourishment to the developing embryo.