What are the steps involved in the formation of root nodule?
Nodule formation involves a sequence of multiple interactions between Rhizobium and the roots of the host plant. Stages in the nodule formation are summarised as follows: Steps in the development of root nodules: (a) When a root hair of a leguminous plant comes in contact with Rhizobium, it is deformed due to the secretion from the bacterium. (b) At the site of curling Rhizobia invades the root tissue and proliferate within root hairs. (c) Some bacteria enlarge to form membrane-bound structures, bacteroids which cannot divide. (d) The plants form the infection thread, made up of plasma membrane that grows inward, separating the infected tissue from the rest of the plant. (e) Cell division is stimulated in the infected tissue and more bacteria invade the newly formed tissues. (f) It is believed that a combination of cytokinin produced by invading bacteria and auxins produced by plant cells, promotes cell division and extension, leading to nodule formation.
