Question

For nitrogen fixation, the pigment useful is

• A. Nitrogenase.
• B. Haemoglobin.
• C. Myoglobin.
• D. Leghaemoglobin.

Answer 1

Answer: (D)

Leghaemoglobin.

Plants cannot consume atmospheric nitrogen directly, because in atmosphere nitrogen occurs in stable diatomic form. The atmospheric nitrogen needs to be converted into plant usable forms like nitrate, nitrite and ammonium ion. This process is called as nitrogen fixation.

Rhizobium is a microaerobic bacteria, which occurs in root nodules of legume plants in symbiotic association. Rhizobium bacteria nodule is pink coloured due to presence of a bacterial pigment called as leghaemoglobin. This pigment binds excess oxygen present in nodules. Free oxygen is harmful for the nitrogenase enzyme of Rhizobium. Rhizobium bacteria reduces atmospheric nitrogen into ammonium ions using reducing power obtained from host plant.