Question

What do you understand by symbiotic nitrogen fixation? Describe the role of leghemoglobin in nitrogen fixation. Outline the process of nitrogen fixation as it takes place in a bacteroid inhabiting a legume nodule.

Answer 1

Hint: Symbiotic nitrogen fixation is the process of converting nitrogen into a suitable form (ammonia) for agriculture using bacteria. It is a part of a mutualistic relationship in which a niche is provided by the plants.

Complete answer:
Generally, the process of converting nitrogen into ammonia or other nitrogenous compounds is called Nitrogen Fixation.

- Nitrogen Fixation is the most essential process for making nitrogen-containing organic compounds such as proteins, amino acids, and nucleic acids.

- Atmospheric nitrogen (molecular dinitrogen) is generally not a reactive molecule, which is converted into a suitable form by using biological and non-biological processes.

- Nitrogen fixation occurs naturally in soil, air by using microorganisms, lightning respectively. Micro-organisms including cyanobacteria, Azotobacteraceae, rhizobia are employed in nitrogen fixation.

- Leghemoglobin is a pink-colored pigment found in the root nodules of leguminous plants, along with the enzyme nitrogenase. Leghaemoglobin acts as an Oxygen Scavenger mainly used to protect the nitrogenase enzyme (highly sensitive to oxygen) found in the leguminous plants.

- As hemoglobin acts as a carrier of oxygen in our body, Legume nodule acts as a carrier of oxygen to the bacterium it is named as leghaemoglobin.

- The best example of nitrogen fixation occurs in plants is the association between legumes and rhizobium. Mutualism is the process of the relationship between both organisms. Rhizobium helps in synthesizing a large number of energy molecules (ATP) for the conversion of ammonia like that legume helps rhizobia with its nutrients to the bacteroids, therefore rhizobia and legume are mutually dependent on each other.

Note: A legume is a plant or fruit or seed in the Fabaceae family used as grains or pulses for human consumption, green manure, livestock, etc..,
The German agronomist Hermann Hellriegel and the Dutch microbiologist Martinus Beijernick discovered the process of biological Nitrogen fixation.