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Pollen tube elongation is an integral stage in the plant life cycle. The pollen tube acts as a conduit to transport the male gamete cells from the pollen grain—either from the stigma (in flowering plants) to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms.
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.
One prime example of chemotropism is seen in plant fertilization and pollen tube elongation of angiosperms, flowering plants. [4] Unlike animals, plants cannot move, and therefore need a delivery mechanism for sexual reproduction. Pollen, which contains the male gametophyte is transferred to another plant via insects or wind. [5]
Since most plants carry both male and female reproductive organs in their flowers, there is a high risk of self-pollination and thus inbreeding. Some plants use the control of pollen germination as a way to prevent this self-pollination. Germination and growth of the pollen tube involve molecular signaling between stigma and pollen.
The pollen tube is an excellent model for the understanding of electrotropism and plant cell behavior in general. [6] They are easily cultivated in vitro and have a very dynamic cytoskeleton that polymerizes at very high rates, providing the pollen tube with interesting growth properties. [7]
The B requirement is much higher for reproductive growth than for vegetative growth in most plant species. Boron increases flower production and retention, pollen tube elongation and germination, and seed and fruit development. [12] A deficiency of B can cause incomplete pollination of corn or prevent maximum pod-set in soybeans. [12]
Antibiotic use was not associated with an increased risk of cognitive impairment and dementia in healthy older adults, according to a recent study.
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.