Tuesday, August 3, 2010

Anthesis of Flowers

The process of flowering is called anthesis.


Before opening the flower bud is similar to the one-wintering buds. In the petals serve as protection. The opening of the flower bud can be achieved by various mechanisms:

* Reversible accumulation of ions. This has been clearly demonstrated to date just in Gentiana kochiana.
* Programmed cell death in defined areas of the petals.
* Loss of water a day and refilling during the night. This occurs for example in Silene Saxifraga, which is nachtblühend and the petals roll up on the day due to water loss.
* Differential growth of the outside and inside of the petals. In tulip petals, the inner side of the lower 10 ° C growth optimum than the outside, leading to an opening in the morning and closing in the evening.

An important factor for the spread of the petals is the increase of turgor, which usually is done by increasing the sugar concentration due to degradation of high molecular weight carbohydrates (starch such as roses, daylilies around fructans). This is accompanied by an expansion of the cell wall. The information on the role of plant hormones are contradictory in the literature. [15] The opening of the flowers is triggered by external factors. In nachtblühenden species often is the increased humidity in the evening the trigger. On increase in temperature are particularly Vorfrühlingsblüher (Snowdrop (Galanthus nivalis), crocus (Crocus spp.)). A third group reacts to light, such as the daisy (Bellis perennis). The opening and closing of long-lived flowers by day or night is done by the same mechanisms and is subject to an endogenous rhythm. The cell physiological and especially the genetic background of the flowers opening and closing are not well known until now.

The closing of the flowers can be achieved by differential growth or by reversible Turgoränderungen. In these cases, a repeated opening and closing is possible. Turgor by senescence leads to the permanent closure of the flower.

Herkogamie: When the ovary is caper about the stamina raised (here Capparis spinosa)

Pollination is the transfer of male pollen to the female organs of conception: the micropyle in gymnosperms, the scars in the angiosperms. The pollination is therefore not the same as fertilization. Pollination can this happen with the pollen of the same individual (self-pollination, autogamy), or with the pollen of another individual (cross-pollination, allogamy).

Self-pollination, however, the reduced genetic variability. There are various adaptations of plants to avoid self-pollination or self-fertilization:

* Herkogamie is the spatial separation of anthers and stigmas, so that a selfing is not possible. When caper (Capparis spinosa), the whole stamp is lifted by Gynophor, so the scar is above the anthers in the approach path of pollinating insects.
* Dichogamy is the temporal separation of the maturation of stamens and ovary. Accordingly, there are predecessors (Proterandrie) and vorweibliche flowers (Proterogynie). The simultaneous maturity called homogamy.

Dichogamy and Herkogamie can indeed prevent the pollination within a flower, but not from one flower to another of the same plant (Geitonogamie). Therefore, many species have developed other mechanisms to avoid:
Pollination by birds (Ornithophily), here by a Rufous Hummingbird
In Central Europe provides most of the honey bee pollination work

* Self-incompatibility: This is prevented by genetic factors, a self-fertilization. Often such incompatibility systems also morphologically recognizable (Heteromorphie) are: a well-known example is the heterostyly the primroses (Primula).

There are, depending on the type of pollinator three major adaptation syndrome: pollination by wind (Anemophily), water (hydrophilic) and animals (zoophilia). The gymnosperms are wind-pollinated primary, while the first angiosperms were probably tierbestäubt primary. Only secondarily have developed several times within the angiosperms wind and water pollination. The main features of each syndrome are:

* Anemophily: inconspicuous flowers reduced, organ number, or Monözie Diözie frequently, dense, often hanging inflorescences; little or no Pollenkitt; smooth pollen surface, scars with a large surface, one or few ovules per flower and no nectar.
* Hydrophilicity: inconspicuous flowers; Monözie Diözie or frequent, occurrence of air tissues; unwettable pollen walls, filamentous pollen grains, stigmas and large surface, or a few seeds per plant flowering.
* Zoophilia: The tierbestäubten plant is not flowering as a morphological unit in the foreground, but the flower as a functional unit. This often corresponds to the blossom of a flower (tulip), but often many flowers are united into a flower, which is then called Pseudanthium. Examples are all composites (such as the daisy) and Umbelliferae (carrot). Rare is the case that a flower is several flowers, as in the iris (Meranthium). The main features of zoophilic flowers are hermaphroditic flowers or pseudanthia; Angiospermie, bold color and / or smell, pollen and / or nectar as food supply, or Täuscheinrichtungen; pollen surface and heavily sculpted much Pollenkitt.

In the gymnosperms, the pollen grains reach the micropyle of the ovules. Usually they are drawn by pollination to drying of the drop in the pollen chamber. In the pollen chamber, depending on the clan, the sperm released and the pollen tubes germinate. Between pollination and fertilization may take up to six month (some cycads).

In the angiosperms the pollen grain reaches the stigma of the stamp. A special Pollenschlauchleitgewebe can reach the pollen tube from the stigma to the ovules. Does the overgrown pen only a single tissue so that pollen tubes can reach the stigma of a carpel of the ovules of another fruit leaf, called the whole of the vascular tissue Compitum.

Are the pollen tubes or sperm reached the egg, it comes to proper fertilization. In the angiosperms, in Gnetum and Ephedra there is a double fertilization: In the angiosperms of either sperm nuclei fuses with the egg and forms the zygote. The second fuses with the diploid embryo sac already core to the triploid Endospermkern from which arises the nutritive tissue (endosperm) of the seeds. In Ephedra, the second sperm nucleus fuses with the ventral canal cell of the archegonium, merge the two Gnetum in sperm cells with two Gametophytenzellen. Of the two resulting zygotes developed in each case usually only one.

After fertilization, the zygote develops into an embryo, the ovule to the seed and the flower to the fruit.

The flowers are used as sexual organs in plants always made new, in contrast to those of animals. The lifetime is accurately measured, since flowers consume large resources, and the scar is also a key entry point for pathogens. Already pollinated flowers were pollinated with non-compete unnecessarily to pollinator.

An important trigger for senescence (aging) is the pollination with pollen. This significantly reduced in most species, the life of the flower. In many plants, pollination triggers the formation of the plant hormone ethylene, which in turn triggers the senescence of the petals. Other species are insensitive to ethylene, their senescence mechanism is unknown. On organ-level crown die after pollination, from the stamens and pistil, while the ovary to fruit development. The decay is accompanied by a remobilization of the ingredients, similar to the senescence of leaves.

Source : http://de.wikipedia.org/wiki/Bl%C3%BCte

See Also: Sending Flowers, Online Florist, Florist

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