Sunday, September 20, 2015

Double fertilization in Angiosperms


Fertilization in plants are fusion process of male gametes (sperm) and female gametes (ovum) that occurs at the base of the pistil to form embryo. There are two kinds of fertilization in plants, namely single and double fertilization. Single fertilization occurs in gymnosperms while double fertilization occurs in angiosperms (flowering plants).

Angiosperms experiencing double fertilization to form an embryo and endosperm (food reserves). The process occurs in two fertilization process, as follows:

  • Fusion of a sperm with ovum (egg) to form a zygote that will develop into an embryo.
  • Fusion of another sperm with polar nuclei to form the endosperm (food reserves).

Fertilization will be preceded first by the pollination process, the fall of pollen on the stigma. The nucleus in the pollen will divide to form two sperms and a tube cell nucleus. After a few moments, the pollen will germinate to form pollen tubes as the path to the embryo sac. There are embryo sac at the base of the pistil and is the site of fertilization. Sperms walk along the pollen tube to reach the embryo sac.

Double fertilization process

Tube cell nucleus would walk in front of sperms because of its role as a guide for both sperm. Having reached the embryo sac, a sperm will fertilize the ovum to form a zygote and another sperm will fertilize polar nuclei to form endosperm.

Eggs are haploid (n) will be fertilized by sperm that are haploid (n), so that it will produce a diploid zygote (2n). Polar nuclei will be fertilized by sperm to form the endosperm. Endosperm is triploid (3n), because it represents the union of two polar nuclei and a sperm that each is haploid.

Embryo will develop into a new individual plant, while the endosperm is a food reserve for the development of the embryo. Endosperm will be used as a first food source on seed germination process.

Double fertilization occurs only in angiosperms, while gymnosperms has a different process called single fertilization. Single fertilization does not produce the endosperm as food reserves.

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