Double Fertilization in Flowering Plants:
Double fertilization is a complex fertilization mechanism for flowering plants. This process involves the joining of a female gametophyte is called an embryo sac with two male gametes also called sperm. As a result of fertilization, the zygote (2n) is formed which grows into an embryo within the seed.
Process of Double Fertilization in Flowering Plants:
1. Transference of mature pollen grains from anther takes place to the stigma of the same flower or different flowers.
2. The pollen grain becomes turgid and swollen by absorbing sugary stigmatic fluid. The inner wall or intine of the pollen grain is stretched and comes out in the form of a pollen tube through the germ pore.
3. Prior to the formation of the pollen tube, the nucleus of the pollen grain divides to form two daughter nuclei of which the larger one is called the tube nucleus and the smaller one is called the generative nucleus.
4. The growth of the pollen tube is influenced by the sugary substances secreted by the stigma.
5. The pollen tube grows in length through the style, and the tube nucleus lies at the of the pollen tube. The generative nucleus which lies behind the tube nucleus now divides to form two male gametes.
6. The entry of the pollen tube within the ovule depends upon the types of the ovule and the point through which it enters within the ovule. Entry through the micropyle is called porogamy, and entry through the chalaza is called chalazogamy. If it enters through the integuments the process is called mesogamy.
7. After entering the ovule, it makes its way by destroying the nucellar tissue toward the embryo sac. The pollen tube penetrates the embryo sac, the tip of the pollen tube gets disorganized and the male gametes are discharged into it.
8. In a double fertilization process, involves the joining of a female gametophyte also called the embryo sac with two male gametes also called sperm. It beings when a pollen grain adheres to the stigma of the carpel, the female reproductive structure of a flower. The pollen grain then takes in moisture and begins to germinate, forming a pollen tube that extends down forward the ovary through the style.