Question

How do nitrogen fixing bacteria and the plants they associate with come together?

Answer 1

The nitrogen fixing bacteria (rhizobia) attracted by the sugars , amino acids etc released by the host legum, multiply and colonise the surroundings of roots and get attached to epidermal and root hair cells. The root hairs curl and the bacteria invade the root - hair. An infection thread is produced, carrying the bacteria into the cortex of the root. Bacteria initiate nodule formation in the cortex of the root,. Then the bacteria released from the thread into the cortical cells of the host stimulate the host cells to divide. Thus leads to the differentiation of specialiaed nitrogen fixing cells. The nodule thus formed establishes a direct vascular connection with the host for exchange of nutrients.