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The actin cytoskeleton has proven to be critical in assisting pollen tube growth. [21] In terms of spatial distribution, actin filaments are arranged into three different structures within the pollen tube. [21] Each unique arrangement, or pattern, contributes to the maintenance of polarized cell growth characteristic of the pollen tube.
During germination, the tube cell elongates into a pollen tube. In the flower, the pollen tube then grows towards the ovule where it discharges the sperm produced in the pollen grain for fertilization. The germinated pollen grain with its two sperm cells is the mature male microgametophyte of these plants. [2]
The best studied mechanisms of SI act by inhibiting the germination of pollen on stigmas, or the elongation of the pollen tube in the styles. These mechanisms are based on protein-protein interactions, and the best-understood mechanisms are controlled by a single locus termed S, which has many different alleles in the species population.
Hydrolytic enzymes are secreted by the pollen tube that digest the female tissue as the tube grows down the stigma and style; the digested tissue is used as a nutrient source for the pollen tube as it grows. During pollen tube growth towards the ovary, the generative nucleus divides to produce two separate sperm nuclei (haploid number of ...
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]
(Typically when pollen encounters a receptive stigma, a series of changes occur which ultimately lead to the growth of a pollen tube down the style, allowing for the formation of the zygote.) Empirical investigation has demonstrated that these barriers act at many different developmental stages and species can have none, one, or many barriers ...
When pollen competition occurs, the competitive ability is determined by differences between tube growth rate or the time it takes for germination to occur. [4] Pollen completion is increased when pollen is not limiting and when pollen is in abundance relative to the number of ovules present in the ovary, but this does not guarantee pollen ...