Question

Leghaemoglobin helps in
A. Nitrogen fixation
B. Protecting nitrogenase from Oxygen
C. Destroy bacteria
D. Transport of food in plant

Answer 1

Hint: Nitrogen fixation is a process in which the environmental nitrogen (N2) is converted to ammonia by the action of enzyme nitrogenase in leguminous plants, symbiotically associated with the Rhizobium bacteria.

Complete answer:
- In the roots of leguminous plants, a nodule is formed after a number of events. These events comprise of accumulation of the Rhizobium bacteria around the root hair, secretion of certain chemicals and Nod factors, curling of the root hair, bacterial invasion, formation of an infection thread, and ultimately nodule formation in the inner cortex.
- The nodule thus formed contains all the biochemical components required for nitrogen fixation like nitrogenase and a red-pink colored pigment called leguminous hemoglobin or leg-hemoglobin (LHb)
- It is pink in color due to the presence of leg-hemoglobin pigment in which haem is a bacterial product whereas the globin is a plant product. It can thus be referred to as a symbiotic pigment and it is present in the cytoplasm of the nodule or bacterial surface.
- The enzyme nitrogenase is highly sensitive to molecular oxygen and only works in anaerobic conditions. It is the function of leg-hemoglobin to provide anaerobic conditions by acting as an oxygen scavenger.

Therefore, the answer is (B) Protecting nitrogenase from oxygen.

Note:-
- Rapid cell division resulting in nodule formation is called “Hyperplasia”
- Legume-Rhizobium alone can fix 25-60 kg of nitrogen per hectare annually.
- Rhizobium and Frankia have an aerobic free-living life in the soil. However, during nitrogen fixation, they become anaerobic to provide a functional environment for the enzyme nitrogenase.
- Uprooted common pulse plants show spherical outgrowths before flowering on the root, which are actual nodules.