Question

Explain the role of pink pigment in the root nodule of legume plants. What is it called?

Answer 1

Hint: The nodules of the roots help in nitrogen fixation with the help of bacteria called rhizobia. The atmospheric nitrogen is changed into ammonia by rhizobia. This ammonia is further used in the formation of nucleotides and amino acids.

Complete answer:
The oxygen-carrier and hemoprotein which are found in the root nodules of the leguminous plants. This is known as leghemoglobin. This is symbiotic haemoglobin and helps in the nitrogen fixation of the legumes. It
provides an ample amount of oxygen to the bacteria for respiration. Leghaemoglobin helps in the protection of the nitrogenase enzyme from getting denatured. It occurs within the cytoplasm of the cell. It is red to pink in colour. It also contains iron, that is it is iron-containing haemoglobin. As it is a respiratory pigment, it helps in the oxygen supply to the bacterial cells. As nitrogenase is sensitive to oxygen supply so the supply of oxygen needs to be adequate and continuous. Lb facilitates oxygen diffusion to the symbiotic
bacteria. The young nodules are incapable of fixing nitrogen to the plant. They are grey or white at this stage. As soon as the nodules start growing in size, the nitrogen fixation ability is developed in them. This also gradually leads to the red or pink colour of the nodules.

Note: Most of the nodules are present in the centre of the taproots. Generally, the ability to fix nitrogen to the nodules are lost annually as the plant feeds the fruit and its parts. Leghaemoglobin or Lb has a similar structure as that of haemoglobin.