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Lipids at the surface of the stigma may also stimulate pollen tube growth for compatible pollen. Plants that are self-sterile often inhibit the pollen grains from their own flowers from growing pollen tubes. The presence of multiple grains of pollen has been observed to stimulate quicker pollen tube growth in some plants. [2]
Pollen germination is facilitated by hydration on the stigma, as well as by the structure and physiology of the stigma and style. [2] Pollen can also be induced to germinate in vitro (in a petri dish or test tube). [13] [14] During germination, the tube cell elongates into a pollen tube.
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.
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 ...
When a pollen grain adheres to the stigma of a carpel it germinates, developing a pollen tube that grows through the tissues of the style, entering the ovule through the micropyle. When the tube reaches the egg sac, two sperm cells pass through it into the female gametophyte and fertilisation takes place. [8]
In angiosperms the ovule is enclosed in the carpel, requiring a specialised structure, the stigma, to receive the pollen. On the surface of the stigma, the pollen germinates; that is, the male gametophyte penetrates the pollen wall into the stigma, and a pollen tube, an extension of the pollen grain, extends towards the carpel, carrying with it ...
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.
Stigma can vary from long and slender to globe shaped to feathery. [4] Pollen is typically highly desiccated when it leaves an anther. Stigma have been shown to assist in the rehydration of pollen and in promoting germination of the pollen tube. [5] Stigma also ensure proper adhesion of the correct species of pollen.