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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]
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 ...
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.
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.
The growth of the pollen tube is controlled by the vegetative (or tube) cytoplasm. 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.
When a pollen grain lands close enough to the tip of an ovule, it is drawn in through the micropyle ( a pore in the integuments covering the tip of the ovule) often by means of a drop of liquid known as a pollination drop. The pollen enters a pollen chamber close to the nucellus, and there it may wait for a year before it germinates and forms a ...
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 stigma is variable in shape, feathery in the case of grasses, head-shaped in Citrus, lobed in Cucurbita, petaloid in Canna and even inverted umbrella-shaped in the case of Sarracenia. It has structural peculiarities that allow the germination of pollen and the development of the pollen tube that will reach the ovules.