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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.
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 ...
In this mechanism, self pollen germinates and reaches the ovules, but no fruit is set. [47] [48] LSI can be pre-zygotic (e.g. deterioration of the embryo sac prior to pollen tube entry, as in Narcissus triandrus [49]) or post-zygotic (malformation of the zygote or embryo, as in certain species of Asclepias and in Spathodea campanulata [50] [51 ...
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.
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.
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.
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 ...
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.