The plastid is a cellular Organite having a clean DNA, it is known as semi-autonomous. A plastid has a membrane interns and an external membrane which form the envelope plastidiale. One meets it in the cells eucaryotes of all the chlorophyllian plants (algae and plants). It is certainly the fruit of the evolution of a Symbiose between a vegetable cell and a photosynthetic Bactérie (=théorie of the Endosymbiose).

Genetic material

DNA plastidial slightly differs from the DNA of the cellular core and DNA mitochondrial. In particular by a stronger presence for the couple Guanosine - Cytosine.

The content of DNA is higher in the plastids than in the Mitochondries.

The DNA plastidial circular measurement between 0,04mm and 0,3 mm length.

Types of plastids

One distinguishes from many types of plastids, of which 6 are interconvertibles between them:

• the Proplaste not differentiated S, or plastids.
• the Chloroplast S, where the Photosynthèse takes place; they contain Chlorophylle.
• the chromoplastes. They contain pigments other than the Chlorophylle: Carotenoid S (of which xanthophylls or lycopene).
• the Leucoplast S, without pigment.
• the amyloplastes are used with storage of the grains as Amidon.
• the étioplaste S, at the plants which miss light.

A plastid can change type. It is the process of interconversion plastidiale. For example: a leucoplast of Potatoes can be transformed into chloroplast with the light; a chloroplast of Citron becomes chromoplaste during the maturation of the fruit.

There exist also the Oléoplaste S, the Protéoplaste S,…

Moreover, one finds a plastid vestigial at some Apicomplexa (such as the protozoon Plasmodium falciparum , agent of the Malaria), the Apicoplaste, surrounded by two double membrane S , it is not capable of photosynthesis.

Comparison

Proplaste

• Plastid
• Chloroplast and étioplaste
• Chromoplaste
• Leucoplast
• Amyloplaste
• Statolithe
• Oléoplaste
• Protéinoplaste

References

• Henri Camefort, Morphology of the vascular plants: cytologie.anatomie.adaptations , Doin, 1996, 2nd ED. (the 7th pulling), 432 p., p.32-49
• {{pdf}} course of DEUG on line.

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