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In order for fertilization to occur, there is rapid tip growth in pollen tubes which delivers the male gametes into the ovules. A pollen tube consists of three different regions: the apex which is the growth region, the subapex which is the transition region, and the shank which acts like normal plant cells with the specific organelles.
In vitro double fertilization is often used to study the molecular interactions as well as other aspects of gamete fusion in flowering plants. One of the major obstacles in developing an in vitro double fertilization between male and female gametes is the confinement of the sperm in the pollen tube and the egg in the embryonic sac.
After the pollen tube enters the gametophyte, the pollen tube nucleus disintegrates and the two sperm cells are released; one of the two sperm cells fertilises the egg cell (at the bottom of the gametophyte near the micropyle), forming a diploid (2n) zygote. This is the point when fertilisation actually occurs; pollination and fertilisation are ...
The pollen enters a pollen chamber close to the nucellus, and there it may wait for a year before it germinates and forms a pollen tube that grows through the wall of the megasporangium (=nucellus) where fertilisation takes place. During this time, the megaspore mother cell divides by meiosis to form four haploid cells, three of which degenerate.
In plants with SI, when a pollen grain produced in a plant reaches a stigma of the same plant or another plant with a matching allele or genotype, the process of pollen germination, pollen-tube growth, ovule fertilization, or embryo development is inhibited, and consequently no seeds are produced.
Pollen itself is not the male gamete. [4] It is a gametophyte, something that could be considered an entire organism, which then produces the male gamete.Each pollen grain contains vegetative (non-reproductive) cells (only a single cell in most flowering plants but several in other seed plants) and a generative (reproductive) cell.
Pollen tube attrition is the failure of a pollen tube that is caused by inhibiting tube growth before fertilization can occur. This phenomenon is another way through which CSI can act. This is accomplished by failing a higher proportion of self-pollen tubes which will end up favoring fertilization by outcross pollen. [8]
The pollen tube releases two sperm nuclei into the ovule. In gymnosperms, fertilization occurs within the archegonia produced by the female gametophyte. While it is possible that several egg cells are present and fertilized, typically only one zygote will develop into a mature embryo as the resources within the seed are limited.