Pollination

Pollination

Pollination is the process by which pollen is transported from the male to the female part of the reproductive system.
Pollination is the main reproduction mechanism of plant species belonging to Gymnosperms and Angiosperms.
There are two types of pollination, namely: self-pollinating or self-pollinating and cross-pollination or heterogeneous pollination.
– The first occurs when the pollen passes directly from the anther of a flower to the stigma of the same flower. The plants that use this system are called autogamous.
– The second is obtained when the pollen is transported from the anther of a flower to the stigma of the flower of a different individual of the same species. The plants that use this system are called allogame.
On the other hand, depending on the system or transport vehicle pollen undergoes pollination, it is defined in different ways:
entomogama or entomophilous pollination, obtained through insects;
– zoogama pollination, obtained through various types of animals, such as reptiles, mammals, molluscs, etc .;
ornithogam or ornithophilous pollination, obtained by transporting pollen through birds;
anemogama or anemophila pollination, obtained by transporting pollen through the wind;
hydrogama or hydrophilic pollination, obtained by water;
artificial pollination, which is the transport of pollen through humans.
A special pollination process is also self-pollination. This mechanism occurs when the pollen falls from the anthers on the stigmas of the same flower. However, self-pollination is only possible in hermaphrodite flowers, but is often prevented by physical or chemical barriers. Self-pollination is frequent in short-lived annual plants and is even required in cleistogamous species (plants with flowers that do not hatch).
However, since self-pollination does not allow for increased genetic variability (a very important factor for life), plant species adopt various precautions to avoid it.

Angiosperms have evolved particular mechanisms to avoid self-pollination. One of these is the production of unisexual flowers on individuals of different sexes (dioecious species). Other mechanisms are known in species with hermaphrodite flowers and in the monoecious ones. One of the most frequent is the maturation of the gynaeceum and androcean at different times: phenomena defined respectively proterogiria and proterandrìa.
One of the most implemented mechanisms to avoid self-pollination is self-incompatibility, that is the characteristic of many plant species that are unable to produce zygotes with its own pollen. Self-incompatibility is genetically controlled in many species by multiple alleles of a gene called S. Both gametophytic self-incompatibility and sporophytic self-incompatibility are recognized.
Another form of pollination within the same plant is geitonogamy; this mode occurs when the pollen of a flower’s anther is transported to the stigma of another flower of the same plant, which is therefore called self-fertile.
In cross-pollination instead the pollen of a plant is transported on the stigma of a flower of another individual of the same species.
Pollination is a necessary factor for the propagation and continuation of life and represents an important factor for the qualitative and quantitative aspects related to agricultural production.
In fact, in agriculture, pollinators promote a richer and better production and in some cases make it possible (without them we would not have cherries, apples, melons and courgettes). Pollinators can be wild, like bumblebees, or bred by humans, like bees.
In this sense the modern use of biocides (insecticides, herbicides, etc.) represents a great danger for the continuation of life itself on Earth, as it affects the continuous and constant depletion of insects, fauna and pollen transmission factors.




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