Double Fertilization

What is double fertilization? To begin with, angiosperms are capable of both asexual and sexual reproductions. Double fertilization is basically a fertilization process that involves combining the megagametophyte with two sperms. The process starts off with a pollen grain on the stigma and then the pollen grain will suck in nutrients and germinate, eventually formulating a pollen tube that will go into the ovary. At the end the pollen tube will release two sperm in the megagametophyte. The surviving megaspore undergoes three rounds of mitosis and then creates eight haploid nuclei. the eight nuclei share the same cytoplasm, thus creating an embryo sac. Inside the embryo sac, cell walls form between the nuclei. After three antipodal cells form opposite of the ovule, and three form near the micropyle, then two polar nuclei remain together in one large central cell. The egg cell and the single cell in partnership with the polar nuclei will take part in double fertilization. before this process truly can occur, the male gametes must travel into the female's reproductive organs. the generative cell then travels down the pollen tube and then behind the tube nucleus. the cell divides by mitosis to produce two haploid sperm cells. the pollen tube then reaches the micropyle in the ovule and releases sperm cells. the synergid degenerates and of the two sperm cells, the egg cell will be feritilized and a diploid zygote will be produced. the sperm mixes with the polar nuclei and then fertilizes them, creating a triploid cell. Zygote -> embryo, triploid cell -> endosperm = food supply of embryo.

There have been questions as to how double fertilization could produce twin sperm cells. Professor Nam of POSTECH reports that the discovery of a gene that has a big role in allowing the reproductive cells to divide to form twin sperm cells is actually true. the gene is called FBL17 and is required to spark the destruction of another protein that inhibits cell division.

Sources: http://www.science20.com/news_releases/fbl17_discovery_gene_behind_%E2%80%98plant_sex_mystery%E2%80%99
http://bcs.whfreeman.com/thelifewire/content/chp39/3902001.html
http://en.wikipedia.org/wiki/Double_fertilization