Question

What is the function of the two male gametes produced by each pollen grain in Angiosperms?

Answer 1

Two male gametes are formed in the angiosperms that lead to double fertilization in them. It is a unique feature that takes place only in angiosperms. Thus, fertilization takes place twice in the same embryo sac.

Complete answer:
We all know that in angiosperms or flowering plants, specialized structures called flowers are the place where pollen grains and ovules are developed. Seeds are enclosed in the fruit. The angiosperm phylum is an exceptionally large group of plants and these plants usually occur in a wide range of habitats.

The male sex organ present in a flower is called a stamen. Each stamen consists of a slender filament with an anther at the tip. The anther on meiosis produces pollen grains that are involved in reproduction. The female sex organ in a flower is the pistil or the carpel is referred to as the female sex organ that is generally present in all kinds of flowers. This pistil consists of an ovary that contains one to many ovules. The embryo-sac formation is preceded by meiosis. The cells of an embryo-sac are generally haploid, which is n. Each embryo-sac has a three celled egg apparatus out of which one is an egg cell while the other two synergids, three antipodal cells and the remaining two are polar nuclei.

Pollen grain, after dispersal from the anthers, is carried by winds or various other agencies to the stigma of a pistil. The pollen grains are germinated on the stigma. The resulting pollen tubes that are formed during this process penetrate through the tissues of stigma and style and later reach up the ovule. The pollen tube that is formed now enters the embryo-sac in which two male gametes are discharged. As this process involves fusion two times so this event is called double fertilization which is a unique event that is generally found in angiosperms. The synergids and antipodals degenerate after fertilisation. During these events, the ovules develop into seeds and the ovaries develop into a fruit.

THE FUNCTION OF TWO GAMETE IS:
- After discharge from the pollen tube, one of the male gametes fuses with the egg cell to form a diploid oospore which is called syngamy.
- The second male gamete moves down to the centre of the embryo sac and fuses with the diploid secondary nucleus to form a triploid (3x) primary endosperm nucleus.

Note: The process of double fertilization was discovered by Nawaschin in Fritillaria and Lilium in the year 1898 but it was later confirmed by Guignard. The process of double fertilisation is characteristic of all angiosperms except few members due to a lack of hormones. In total 5 nuclei (2 male nuclei + one egg cell nucleus + 2 polar nuclei) are involved in double fertilization.