a. Legume plant and nitrogen-fixing bacteria, e.g., chickpea and Rhizobium or Leguminosae or Fabaceae plants and nitrogen fixing-Bacteria.
b.Steps in the formation of root nodules :
- Root hair of the leguminous plant curls upon contact with nitrogen fixing bacterium, which secretes chemicals.
- Nitrogen-fixing bacteria proliferate within curled root hair.
- The plant responds by forming an infection thread of the plasma membrane, which grows inward from the infected cell of the host, separating it from the rest of the plant.
- Cell division is stimulated in the infected tissue and more bacteria invade the newly formed cells, and a nodule is formed.
Auxin from leguminous plant cells and cytokinin from bacteria help in this cell division :
Physiological processes : Photosynthesis and respiration.