Topeltviljastumine

Topeltviljastumine is a unique biological process that occurs in flowering plants, a defining characteristic of angiosperms. It involves the fusion of two male gametes with two different cells within the ovule. This process was first discovered by Sergei Navashin in 1898.

The process begins when a pollen grain lands on the stigma of a flower. It then germinates and grows a pollen tube down through the style towards the ovary. Within the ovary, the ovule contains the female gametophyte, which typically has eight nuclei. The pollen tube carries two sperm nuclei. Upon reaching the ovule, the pollen tube penetrates the embryo sac. One sperm nucleus fuses with the egg cell, forming a diploid zygote. This zygote will develop into the embryo of the new plant.

Simultaneously, the second sperm nucleus fuses with the central cell, which usually contains two polar nuclei. This fusion results in a triploid primary endosperm nucleus. The endosperm serves as a nutritive tissue for the developing embryo, providing it with essential food reserves. Therefore, topeltviljastumine results in the formation of both the embryo and the endosperm, ensuring the successful development and propagation of the plant species. This dual fertilization event is crucial for the reproductive success of most flowering plants.