Question -
Answer -
Nodule formation involves a sequence of multiple interactions between Rhizobium and roots of the host plant. Main stages in the nodule formation are:
(i) Rhizobia multiply and colonise the surrounding of roots and get attached to epidermal and root hair cells (Figure a).
(ii)The root hair curl and the bacteria invade the root hair.
(iii)An infection thread is produced carrying the bacteria into the inner cortex of the root (Figure b and c).
(iv)The bacteria get modified into rod-shaped bacteroids and cause inner cortical and pericycle cells to divide. Division and growth of cortical and peri cycle cells lead to nodule formation.
(v) The nodule thus formed, establishes a direct vascular connection with the host for exchange of nutrients (Figure d).
(vi)The nodule contains all the necessary biochemical components, such as the enzyme nitrogenase and leghaemoglobin. The enzyme nitrogenase catalyses the conversion of atmospheric nitrogen to ammonia, the first stable product of nitrogen fixation.