1997 WWLPT Biology Institute: Life Cycles: Reproduction & Embryological Development

Gametogenesis and Fertilization in Angiosperms

Gametogenesis in Angiosperms occurs in the anthers and the ovules of the flower. In the anther, diploid microspore mother cells undergo meiosis to produce 4 haploid microspores. The nucleus in each of these microspores divides once by mitosis to produce a pollen grain with two haploid cells. This pollen grain is the male gametophyte. One of the cells of the pollen grain contains the tube nucleus which enables the pollen tube to grow down the style of the flower to the ovule. The other cell of the pollen grain, the generative cell, divides mitotically to form 2 haploid sperm.

Meanwhile, in the ovule of the ovary, the megaspore mother cell divides meitotically to produce 4 haploid megaspores. Three of these 4 megaspores disintegrate. The fourth megaspore undergoes 3 cycles of mitosis to produce the female gametophyte, consisting of 7 cells with a total of 8 haploid nuclei. The central cell contains 2 polar nuclei. Three cells are found at each end of the large central cell. The middle cell located near the micropyle, a small opening in the ovule is the egg.

During pollination, a pollen grain lands on the stigma where the pollen will germinate producing a pollen tube that grows through the style to the egg in the ovule. One of the 2 sperm arising from the generative cell will fertilize the egg resulting in a 2n zygote. The other sperm fertilizes the 2 polar nuclei, each haploid, resulting in a triploid (3n) endosperm, a nutritive tissue for the embryo. A seed coat, which is not a product of fertilization, forms around the endosperm. The result is a seed composed of the seed coat, the nutritive endosperm, and the embryo.






Germination of Pollen Tube

Gametogenesis and Fertilization Home Page
Gametogenesis and Fertilization in Angiosperms
Gametogenesis and Fertilization in Mammals
Laboratory Exploration: Pollen Tube Germination
Supplemental Activities on Gametogenesis and Fertilization