Plants are universal producers. They are the source of food, oxygen, provides shelter etc. As plants are a vital element of life, their reproduction is also important. This is attained by fertilization, more precisely double fertilization. Let us have a brief discussion on double fertilization.
What is double fertilization?
Double fertilization is a complex fertilization mechanism of angiosperms which involves the fusion of a female gametophyte with two male gametes. One male gamete fuses with the female egg whereas the second sperm fuses with two polar nuclei to give rise to a triploid body that forms an endosperm.
Also Read: Angiosperms
Double Fertilization in Angiosperms
Angiosperms are flower-bearing plants surrounding us and these flowers are their reproductive units which include male and female reproductive organs. Each contains gametes – sperm and egg cells respectively.
Pollination helps the pollen grains to reach stigma via style. Two sperm cells enter the ovule-synergid cell. This proceeds to fertilization.
In angiosperms, fertilization results in two structures namely zygote and endosperm; thus fertilization is known as double fertilization.
By definition, double fertilization is a complex fertilization method where out of two sperm cells, one fuses with the egg cell and other fuses with two polar nuclei which result in diploid (2n) zygote and triploid (3n) primary endosperm nucleus (PEN) respectively.
Since endosperm is a product of the fusion of three haploid nuclei, it is called triple fusion. Eventually, the primary endosperm nucleus develops into the primary endosperm cell (PEC) and then into the endosperm.
The zygote becomes an embryo after numerous cell divisions.
Development of Embryo
Once fertilization is done embryonic development starts and no more sperm can enter the ovary. The fertilized ovule develops into a seed and ovary tissues develop as fleshy fruit which encloses the seed.
The first stage of embryonic development includes division of the zygote into the upper terminal cell and lower basal cell.
The basal cell develops into suspensor which helps in nutrition transport to the growing embryo. The terminal cell develops into proembryo. Further embryonic development into seed takes in an interval of time.
Significance of Double Fertilization
The significance of double fertilization is mentioned below:
Produces a food supply for the seed
An embryo is produced within the seed during the process of double fertilization. This procedure is also used as an additional food source by some plants.
Provides extra protection to the species
Double fertilization increases the life span of a flowering plant. There are two male gametes. Therefore the chances of them fusing with the female gametes are very high. The endosperm formed after fertilization stores nutrients. So, the plant does not have to allocate energy-intensive resources for the unfertilized egg.
When the embryo starts coming into shape, it starts conserving energy due to double fertilization. The essential supply is found in the seed itself.
Allows Rapid Seed Development
Since two male gametes are involved in double fertilization, the development of seed is more rapid as compared to other forms of reproduction. The nucleus of the endosperm divides quickly to structure the nutrient-rich tissue, which inturn enhances the development of embryo.
Also Read: Fertilization in Plants
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