Question

How many times higher concentration of Molybdenum (Mo) in the root nodules of legumes than their leaves ?

• A. 10 times
• B. 15 times
• C. 20 times
• D. 25 times

Hint:

Molybdenum (Mo) is required in the smallest quantity among plant essential micronutrients, but it is indispensable for nodulation. Remember: Mo in nodules $\approx 10\times$ Mo in leaves.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the relative fold-concentration of the micronutrient Molybdenum (Mo) present in the active root nodules of leguminous plants compared to their foliar tissue (leaves).

Step 2: Key Physiological & Biochemical Role of Molybdenum:

• Role in Nitrogen Fixation: Molybdenum is a critical metallic cofactor of the nitrogese enzyme complex (specifically the Mo-Fe protein subunit) responsible for converting atmospheric nitrogen ($N_2$) into biological ammonia ($NH_3$).

• Enzyme Constituent: It is also an essential component of the nitrate reductase enzyme.

• Accumulation Site: Due to high nitrogese enzyme synthesis inside symbiotic bacteroids within root nodules, legumes translocate significant amounts of Mo to the nodules.

Step 3: Detailed Explation:

• Experimental plant physiology studies demonstrate that Molybdenum content in leguminous root nodules is approximately 10 times higher than that found in non-nodular vegetative tissues like leaves.

• In Mo-deficient soils, symbiotic nitrogen fixation decreases drastically before visible deficiency symptoms appear on the leaves.

• Maintaining adequate Mo levels ($0.1--1.0$ ppm in dry tissue) ensures high functiol activity of bacteroid nitrogese in nodules.

Step 4: Fil Answer:
The concentration of Molybdenum in root nodules of legumes is about 10 times higher than in their leaves. Thus, option (A) is correct.