The pollination is the mode of reproduction privileged plants Angiospermes and Gymnospermes. It is about the process of transport of a grain of Pollen since the cheesecloth (male body) so that this one meets the bodies females of the same species, making possible the Fécondation.
ProcessDuring pollination, the Pollen is transported Anthère with the Stigmate of very the Fleur or another flower of the same species. Once on the mark, the grain of pollen emits a pollen tube which crosses the Style. This pollen tube conveys the male gamètes until the Ovule in order to fertilize it. There exist several strategies used by nature to disperse the pollen of a male anthère to a mark female.
Pollination can also be artificial in order to create Hybride S having the specific qualities inherited the two parents chosen by the hybridor.
Pollination by the animals ( the zoogamy )
The majority of the plants count on the animals to ensure their pollination. The plants which use the zoogamy develop floral bodies sometimes extremely complex in order to attract the pollinating ones.
The entomophilie (entomogamy)Characteristic of a plant which is made pollinate via an insect.
By exploring the flowers in the search of nectar, the Insecte S (enter others the bees, the butterflies, the Diptères or some coleopters) rub with the cheesecloth S, involuntarily collecting grains of pollen (up to 100.000) which they will give up thereafter in another flower. Each insect is often specialized to collect the pollen of one or some species in particular, with the result that pollen often profits from a transport targeted to another flower of the same species.
The ornithophilieWhen pollination is carried out via birds.
The birds with the long pointed nozzle the such hummingbirds are also of important visitors of the flowers. When their long frayed nozzle plunges at the bottom of the corolla in order to draw nectar there, their head rubs with cheesecloths and, inevitably, pollen adheres to their feathers.
The cheiroptérophilieWhen it is carried out via Chauves-souris.
Others Mammalian SSmall marsupials and some Rongeur S also take part in the pollination of several species.
Pollination by the wind (" the anémogamie" or " anémophilie")The simplest method, but the least effective, consists in producing massive quantities of pollen by hoping that the wind transports them to good port. The plant spends thus much of energy to produce pollen; on the other hand, it does not need to work complex structures like coloured flowers, odorous nectar or perfumes in order to attract the pollinating ones. Approximately 10% of the species rely on the wind to ensure their pollination, among which the Graminée S appear, one of the principal persons in charge of the Hay cold.
Pollination by water ( the hydrogamy )Some rare species of watery plants disperse their pollen in water. Their pollen is of very lengthened form, which makes it possible the currents to transport it of a plant to the other.
Marine speciesThe Zostère marinades ( Zostera marina ), present in France and along the east coast of the Canada (and which constitutes one of food of predilection of the Bernache S).
The American Vallisnérie ( Vallisneria americana ) also makes use of water to transport its pollen, but of indirect way. The plant forms at the bottom of water its male and female flowers on different individuals. It releases then its male flowers which go up to surface where they open. The female flowers, as for them, push to surface where they open in their turn, among the male flowers which float around. After the fecundation, which takes place in the air, the female flower is closed again and turned over to the bottom of water to mature its fruit.
Self-fertilization and the cross-fertilizationThe pollination perhaps of type allogame (the ovule is fertilized by pollen resulting from another plant) or autogame (the male bodies fertilize the bodies females of the same flower).
The majority of the plants with flowers being hermaphrodites, one could think that self-fertilization is for them the solution of the simplest reproduction. However, in many cases, they make very to escape from this type of pollination, which ensures certainly the continuation and the stability of the species, but the price from an impoverishment comparable with the Endogamie at the human ones. One thinks in particular that the plants autogames would be unable to adapt to new conditions, created in particular by climatic modifications. The strategy allogame can take very varied forms. It will be noted however that many flowers, for safety reasons, practice at the same time the cross-fertilization and self-fertilization, while others, apparently increasingly many, are exclusively autogames.
The strategy allogame
How to make so that an ovule is not fertilized by its own pollen? The plants use for that of the very diverse means, sometimes complementary (one will not quote here the plants Dioïque S, for whom the problem is inevitably solved since the male and female flowers are not on the same individual):
- the car-incompatibility. It is the most frequent case, encountered at the half of the angiospermes at which one sought this feature.
One currently distinguishes 3 types of car-incompatibility:
- gamétophytique : pollen carries only one Allèle, that carried by its Génome,
- sporophytic: pollen carries the two - or more - alleles carried by the father, however there exist relations of predominance between the alleles of the same species
- post-zygotic car-incompatibility which gathers all the mechanisms leading to the systematic death of the embryos resulting from car-fecundations or fecundations between related (this Is only the observation of the expression of the depression of consanguinity or of real genetic mechanisms?).
the Dichogamie (disjunction of the sexes):
- in time. The male and female sexual organs are not functional at the same time. In general, in fact the male bodies mature before the bodies females, phenomenon called Protandrie . The phenomenon is easily visible on the Géranium S, whose marks develop whereas cheesecloths already disappeared. The opposite phenomenon is called Protogynie (Hellébore, Magnolia).
- in space. the male and female bodies are laid out of such way that the insect cannot reach at the same time the anthères and marks.
- by hétérostylie. The flowers, all hermaphrodites, present various forms imposing the crossing. It is in particular the case of the common Primevère ( Primula vulgaris ), whose certain flowers have a long style and short cheesecloths, while others have on the contrary a short style and long cheesecloths.
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