Double fertilization is the unusual reproductive process that flowering plants go through and there are two fertilization events, not one. The ovule (female reproductive part of plant) has a megaspore (mother) that is diplod (2n) but undergo meiosis to produce four haploid cells (n). Three of these degenerate and one megaspore is left. This remaining megaspore undergo mitosis to produce eight haploid nuclei, making a multinucleate structure called an embryo sac. Three antipodal cells form at the opposite side of the microphyle opening. Two synergids and the egg form near the microphyle opening and two polar nuclei remain together as a central cell. Before fertilizing, a pollen grain lands on the stigma and germinates to send a pollen tube down the style and the ovary. A haploid/generative cell travels down the tube and divides to produce two haploid sperm cells. The pollen tube digests through one of the synergids, the synergid degenerates, and one of the sperm cells fertilizes the egg. The second sperm fuses with both polar nuclei to make a triploid (3n) cell that later becomes the endosperm, the embryo's food supply.
Source:
information from: http://bcs.whfreeman.com/thelifewire/content/chp39/3902001.html
picture from: http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookflowersii.html
No comments:
Post a Comment