Question

The pigment protein present in nodulated roots inhabited by Rhizobium is
A. Nitrate reductase
B. Hydrogenase
C. Leghaemoglobin
D. Plastocyanin

Answer 1

Hint: Root nodules of leguminous plants harbor Rhizobium bacteria. With the help of enzymes these bacteria convert atmospheric nitrogen into ammonium ions.

Complete Answer:
Let's discuss the option and find the correct answer.

Option A: Nitrate reductase in higher plants is proposed to be a homodimer. It is the enzyme which catalyzes the first step in reduction of nitrate to organic forms of nitrogen within the plant. Therefore, this is the incorrect option.

Option B: Hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen. Based on the metal content of their active site hydrogenases are differentiated into three distinct classes. Therefore, this is the incorrect option.

Option C: Rhizobium is symbiotic nitrogen-fixing bacteria present in the roots of leguminous plants. For the formation of root nodules in legumes roots this bacteria is responsible. The nodule contains a biochemical pigment protein called leg-haemoglobin. It functions as an oxygen scavenger. Therefore, this is the correct option.

Option D: Plastocyanin is a copper-containing protein that mediates electron-transfer. It is found in a variety of plants. It participates in photosynthesis. Therefore, this is the incorrect option.

Thus, the correct option is C) Leghaemoglobin.

Note: Rhizobium contains a nitrogenase enzyme which is sensitive to oxygen. These bacteria produce leghemoglobin pigment, which acts as a scavenger of oxygen and binds free oxygen. Thus, protecting the bacterial nitrogenase.