Plants are the 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.
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 fuse with the egg cell and other fuses with two polar nuclei which results 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 a triple fusion. Eventually, the primary endosperm nucleus develops into primary endosperm cell (PEC) and then into endosperm. 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 zygote into the upper terminal cell and lower basal cell. The basal cell develops into suspensor which helps in nutrition transport to growing embryo. The terminal cell develops into proembryo. Further embryonic development into seed takes in an interval of time.
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