Rhizobium

The rhizobiums , or rhizobia ( Rhizobium ), are Bactérie S aerobes of the ground pertaining to the family of the Rhizobiaceae . These bacteria have the capacity to form a Symbiose with plants of the family of the Légumineuse S, of which the most known representatives are: pea, bean, soya, groundnut, clover, alfalfa,…

This symbiosis confers on the Fabacées, the single aptitude among the plants of field crop to nourish itself starting from the Azote of the air.

In condition limiting out of combined nitrogen, the rhizobiums will induce the formation of Nodosité S on the level racinaire or caulinaire of leguminous plants. These Nodosité S will represent true bodies of metabolic exchange between the Bactéries and the Plantes.

This symbiosis with reciprocal benefit will make it possible the bacteria to profit from a micro exceptionally favorable habitat; the Fabacées getting to them a contribution in carbonaceous substrates resulting from the Photosynthesis. In exchange, the Bactérie S will fix and reduce atmospheric nitrogen in Ammonium, directly assimilable by the plants hosts.

External bonds

  • Rhizobia taxonomy

Installation of symbiosis

The piliferous cells of the roots of Fabacées (Fabaceae) emit chemical substances of recognition (standard Flavonoïde S Isoflavonoïde S). These exsudats attracts the bacterium, which in return slackens Lipopolysaccharide S (LPS) coming from its membrane. These LPS have a specific antigenic structure, recognized by the plant. The bacterium “having shown white leg”, it can lyse the wall of the vegetable cell and there be introduced. There is formation of an infectious cord, which progressively ramifies its passage in other vegetable cells. In the cytoplasm, the bacteria are not free, they are gathered in blisters of sequestration. If the cell is Diploïde, it necroses and dies. If it is tetraploid on the other hand, there is formation of a Nodule.

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