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Pollen tubes are an excellent model for the understanding of plant cell behavior. [19] They are easily cultivated in vitro and have a very dynamic cytoskeleton that polymerizes at very high rates, providing the pollen tube with interesting mechanical properties. [20] The pollen tube has an unusual kind of growth; it extends exclusively at its apex.
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.
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]
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.
The first of the cells (the generative cell) is small and is formed inside the second larger cell (the tube cell). The members of each part of the microspores separate from each other. A double-layered wall then develops around each microspore. These steps occur in sequence and when complete, the microspores have become pollen grains. [3]
Skin allergies frequently cause rashes, or swelling and inflammation within the skin, in what is known as a "weal and flare" reaction characteristic of hives and angioedema. [30] With insect stings, a large local reaction may occur in the form of an area of skin redness greater than 10 cm in size that can last one to two days. [31]
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Haematopoietic stem cell transplantation (HSCT) is the transplantation of multipotent haematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood. [ 10 ] [ 11 ] [ 12 ] It may be autologous (the patient's own stem cells are used), allogeneic (the stem cells come from a donor) or syngeneic (from an ...