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Pollen tube elongation is an integral stage in the plant life cycle. The pollen tube acts as a conduit to transport the male gamete cells from the pollen grain—either from the stigma (in flowering plants) to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms.
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.
Microgametogenesis is the process of the formation of the male gametophyte. During pollination, the female gametophyte communicates with the pollen tube to ensure that it comes in contact with the ovule. [6] When contact is made, the pollen tube grows through the micropyle opening into a synergid cell, that dies when this occurs.
The pollen is carried to the pistil of another flower, by wind or animal pollinators, and deposited on the stigma. As the pollen grain germinates, the tube cell produces the pollen tube, which elongates and extends down the long style of the carpel and into the ovary, where its sperm cells are released in the megagametophyte.
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.
If the pollen is compatible it will germinate and begin to grow. [5] The ovary releases chemicals that stimulates a positive chemotropic response from the developing pollen tube. [6] In response the tube develops a defined tip growth area that promotes directional growth and elongation of the pollen tube due to a calcium gradient. [5]
The mechanisms involved in pollen formation and development of the pollen tube are important for pollen selection as well as protein composition of the pollen. [3] Pollen surface proteins are produced in the sporophytic tissue of the anther and have expressed higher levels of purified selection with an increase in adaptive evolution from the ...
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 ...