Question

In root nodules of legumes, leghaemoglobin is important because it:-
A) Acts as a catalyst in transamination
B) Transport oxygen to the root nodule
C) Provide energy to the nitrogen fixing bacteria
D) Acts as an oxygen scavenger

Answer 1

Leghemoglobin's key roles are to promote the delivery of oxygen to the nitrogen-fixing bacteria and to shield the nitrogenase enzyme from oxygen inactivation.

Complete answer:
- The bacterial mechanism by which molecular N2 gas is transferred to reactive, biologically available sources of nitrogen is nitrogen fixation. The plants are not provided with atmospheric nitrogen.
- Atmospheric nitrogen is converted into ammonium compounds by nitrogen-fixing bacteria and made available to plants. Two kinds of bacteria, free-living and symbiotic, exist. Examples of free living bacteria that fix nitrogen include Azotobacter. Rhizobium is an example of a symbiotic nitrogen fixing bacteria.

Now, let us find the solution from the options-
- Rhizobium lives in the root nodules in a symbiotic relationship with legume plants and fixes atmospheric nitrogen. Leghaemoglobin present in the root nodules of legume plants. This functions like a scavenger for oxygen.
- Leghaemoglobin is a scavenger of oxygen that protects nitrogenase during fixation of nitrogen.
- Leghemoglobin is a carrier of oxygen and hemoprotein present in leguminous plants' nitrogen-fixing root nodules. In reaction to the roots being colonised by nitrogen-fixing bacteria, called rhizobia, these plants produce it, as a result of the symbiotic relationship between bacteria and plant.

Thus, the correct answer is option (D) Acts as an oxygen scavenger.

Note: Leghemoglobin has similar chemical and structural to haemoglobin and is red in colour, like haemoglobin. It was originally assumed that within symbiotic root nodules, the heme prosthetic unit for plant leghemoglobin was supplied by the bacterial symbiont.