Question

Given below are two statements
Statement I: In Rhizobium- legume symbiosis large and pink colored nodules are considered good for efficient nitrogen fixation
Statement II: Pink color of the nodules is due to the presence of leg-haemoglobin pigment
In light of the above statements, choose the correct answer from the options given below:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

Pink root nodules contain active leghemoglobin, which maintains microaerophilic conditions within the nodule to protect the oxygen-sensitive enzyme nitrogenase.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Leguminous plants form symbiotic relationships with Rhizobium bacteria.
The bacteria colonize host root hair cells and induce the development of specialized root structures called nodules, where atmospheric nitrogen is reduced to ammonia.

Step 2: Detailed Explanation:
Statement I Analysis: Root nodules can vary in size, number, and internal coloration depending on their physiological activity.
Large, robust nodules concentrated on the primary or tap root are generally indicative of a healthy symbiotic relationship.
When cut open, actively fixing nodules display a characteristic deep pink or reddish-brown internal coloration.
Green, white, or brown nodules indicate old, inactive, or ineffective symbioses. Thus, Statement I is true.
Statement II Analysis: The pink coloration of active nodules is due to the oxygen-binding metalloprotein leghemoglobin.
Leghemoglobin is synthesized through cooperation between the plant host (which produces the globin protein) and the bacterial symbiont (which synthesizes the heme group).
The enzyme nitrogenase, which catalyzes nitrogen fixation, is highly sensitive to free oxygen.
Leghemoglobin acts as an oxygen buffer, binding free oxygen to keep local concentrations low (protecting nitrogenase) while delivering oxygen to the bacteria for cellular respiration. Thus, Statement II is true.
Since both statements are true, the correct option is (A).

Step 3: Final Answer:
Hence, both Statement I and Statement II are true.