Question

The function of leghemoglobin in the root nodules of legumes is
A) Oxygen removal
B) Inhibition of nitrogenase activity
C) Expression of nif gene
D) Nodule differentiation

Answer 1

Leghemoglobin (also haemoglobin or legoglobin) is an oxygen-carrying phytoglobin found in the nitrogen-fixing root nodules of leguminous plants like soybean and alfalfa. As Leghemoglobin sounds similar to haemoglobin the function of it is also similar to the haemoglobin in the blood of the human body.

Complete solution:
As we look through the choices,
A) Oxygen removal is the correct answer because leghemoglobin is the red-coloured pigment found in the root nodules of leguminous plants. So, it combines with oxygen and thus helps in oxygen removal from root nodules. Thus, helping to scavenge the limited free oxygen in the cell and deliver it to mitochondria for respiration. Therefore it is responsible both for buffering oxygen concentration and for delivery of oxygen to mitochondria.
B) Inhibition of nitrogenase activity is the incorrect answer because the function of leghemoglobin is to aid nitrogen fixation in the root nodules of leguminous plants. Hence it cannot inhibit nitrogenase activity.
C) Expression of nif gene is also an incorrect answer because nif genes are genes encoding enzymes involved in the fixation of atmospheric nitrogen into a form of nitrogen available to living organisms where expression of nif gene is controlled by NifA protein.
D) Nodule differentiation is also incorrect because differentiation of nodules is caused by the symbiotic relationship of the plant with nitrogen-fixing bacteria.
Therefore the main function can hence be considered as creating an oxygen free environment by removing oxygen so that nitrogen can occur.

Hence choice - A . oxygen removal is correct answer.

Note:
Even though leghemoglobin carries oxygen, the main function of leghemoglobin in the root nodules of legumes plants is to remove the oxygen so as to fix nitrogen. Thus it creates an oxygen-free environment by carrying away the oxygen to mitochondria.