DOUBLE
FERTILIZATION
Definition-
Double fertilization is a complex fertilization mechanism of flowering plants
which involve the joining of female gametophyte with two male gametes
Process of Double
fertilization:-
Double fertilization is the characteristic features of
Flowering plants (angiosperm) and discovered by Nawaschin in 1898.
1. The transference of pollen grains takes place to the
stigma of same flower or different flowers.
2. Pollen grain becomes turgid and swollen by absorbing
stigmatic fluid and the inner wall (intine) of pollen grain is stretched and
comes out as pollen tube.
3. The nucleus of pollen grain divides to form 2 daughter
nuclei (1 is larger called tube nuclei and 2nd is smaller called
generative nuclei) the generative nucleus divides to from two male gametes.
4. Now the pollen tube enters to ovule as Porogamy (through
micropyle end), Chalazogamy (through chalazal end) or Mesogamy (through integuments).
5. Now the pollen tube penetrates the embryo sac and the two
male gametes are discharged into it.
6. At this time the Embryo sac contain 8 haploid nuclei of
which 3 lie at chalazal end called antipodal cell, 3 at micropylr end called
egg apparatus ( 2 synergids and 1 is egg), and in the centre there is secondary
nucleus or definitive nucleus (2n).
7. Of the two male gametes one fuses with egg forming oospores
or zygote and the other move towards the centre and fuses with secondary
nucleus(2n) to form triploid (3n) endosperm nucleus. Such behavior is called
double fertilization.
8. The triploid cell will then develop into the endosperm a
nutrient rich tissue which provides nourishment to the developing embryo.
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