The nodosities are small blisters being formed on the roots of many species of Plante S, in particular the Fabacée S, under the action of Bactérie S of the kind alive Rhizobium in Symbiose with the plant. In this symbiotic association, the plant provides the carbonaceous substances and the bacteria the nitrogenized substances synthesized starting from the atmospheric nitrogen . This Symbiose makes it possible the plant to fix atmospheric nitrogen thanks to the enzyme Nitrogénase synthesized by the bacterium and of which the plants eucaryotes are deprived.

Stages of the development

• On the level of a root of seedling of soya

The activities coordinated of légumiseuse and a bacterium of the kind Rhizobium depend on the chemical reactions between the two symbiotic partners.

First stage: the infection

The roots secrete chemical substances of the flavonoïde type and isoflavanoïdes, which attracts the bacteria of the type Rhizobium of the vicinity. In answer, the bacteria synthesize and emit factor of coring, known as factors '' nod ''. Under their action, the hairs absorbents change their direction of growth and form a structure in stick of shepherd, who locks up rhizobiums. The bacteria can thus penetrate in the bark (cortical parenchyma), via an infectious net. At the same time, the root starts to answer the infection by a division of the cells of the bark and pericycle of the central cylinder. The blisters containing the bacteria bud in the cells of the bark starting from the end of the ramified infectious net.

Second phase: development of nodosity

The growth continues in the infected areas of the bark and the Péricycle, until these two masses of cells amalgamate and form nodosity. The bacteria cause invaginations of the plasmic Membrane which will amalgamate with the apparatus of Golgi, which allows the projection of the bacterium towards the Cortex racinaire.

Third stage: maturation of nodosity

Nodosity continues its growth, whereas the conducting fabric connecting nodosity to the Xylème and the Phloème of the central cylinder develops. This conducting fabric brings to nodosity the Glucides and other organic substances necessary to the cellular Métabolisme. It transports also the nitrogenized compounds produced in nodosity towards the central cylinder, which will distribute them in all the plant.

See too

• biological Fixing of the nitrogen