Fertilization in flower is a type of sexual reproduction, where the male and female gametes of the stamen and carpel fuse to form a zygote. In a flowering plant, pollen grains released from the anthers contain two sperm cells, which are the male gametes of the flowering plant. An ovary of a flower consists a megasporangium or ovule which includes a seven celled embryo sac. A three celled egg apparatus, a central cell and three antipodal cells are present within the embryo sac. The egg apparatus contains egg cells within the embryo sac, which is the female gamete of a flowering plant.
Thus, like human fertilization, plants also involves the combination of both male and female gametes to form a zygote. For the fertilization to occur, a process of pollination in flower is necessary. Without pollination, fertilization in the plants cannot be achieved.
Content: Fertilization in Flower
Definition of Fertilization in Flower
Fertilization in flower can define as a growth process of flower that involves the fusion of sperm cells carried by the pollen grains and the egg cells contained in an ovule to form a zygote. In flower, the male reproductive part refers to as “Stamen or Androecium”, and the female reproductive part refers to as “Carpel or Gynoecium”. The anther of the male reproductive part carries the male gametes or sperm cells within the pollen sacs of pollen grains or microsporangium. An ovule or megasporangium of the female reproductive part contains the female gametes or egg cells.
By pollination, the pollen grains reach to the top of the female reproductive part, i.e. Stigma. Then, through the pollen tube germination, the passage of sperm cells to the egg cells becomes possible, and fertilization occurs.
Process of Fertilization
A method of fertilization in flowering plant involves the following steps:
First, the anthers elevate by the help of its elongated filaments. Further, the anthers ultimately dangle out of the spikelet is the process refers as “Anthesis”. After Anthesis, pollination immediately occurs. During pollination, anther releases pollen grains that contains the sperm cells.
Then, the pollen grains are transferred to the sticky stigma via some pollinating agents like wind, water and insects. The stigma also receives the pollen grains in the flowering stage or when the spikelet opens.
Germination of Pollen grain
Under favourable conditions, the pollen that sticks to the stigma starts to germinate. On germination, a pollen grain forms a tube refers as “Pollen tube”. The pollen tube acts as a passage from the stigma to an ovule.
Penetration of the tube into the ovule
The pollen tube first penetrates the stigma and grows downwards from style to an ovule and finally the micropyle region of an embryo sac. The sperm cells carried by the pollen grain is released into the tube, which then penetrates through the wall of an ovule. Generally, it takes 15-16 minutes for the pollen tube to reach an ovule. The entry of pollen tube to embryo sac refers as “Pollen-pistil interaction”.
It involves the fusion of male and female gametes of the. The embryo sac contains seven cells, one egg cell, synergid, two polar nucleus and three antipodal cells. A pollen tube enters one of the synergids that surrounding the egg cell and discharges its sperm cells.
One sperm cell or male gamete fuses with the egg cell to form a diploid “Zygote”. The other sperm cell fuses with the two polar nuclei to develop a triploid primary endosperm cell. Thus, the fusion of the male gametes with an egg cell and polar nucleus refers as “Double fertilization”.
A zygote develops into an embryo, and a primary endosperm cell develops into a nutrient-rich endosperm by undergoing mitosis. The endosperm provides nourishment to the developing embryo. After completion of fertilization and all the developmental stages, the ovule transforms into a seed whereas ovary transforms into a fruit.
A process of fertilization in flowers is an important growth event that evolves new species by providing new genetic characters to the plant. Fertilization ensures diploidy of the zygote by the fusion of haploid sperm cell and egg cell. It is essential for the formation of seeds and fruits.