Question

Element associated with urease activity

• A. Ni
• B. Mo
• C. Fe
• D. Co

Hint:

Nickel was the last element to be officially added to the list of essential plant micronutrients (by Dalton et al. in 1987), primarily due to its role in urea metabolism.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Certain trace elements serve as essential metallic cofactors for specific plant and microbial enzymes. Without these metal ions, the enzymes cannot undergo the conformational changes required to catalyze biochemical reactions.

Step 2: Detailed Explanation:
- Nickel (Ni) is an essential micronutrient for plants and microbes because it is the central metallic cofactor in the urease enzyme.
- Urease catalyzes the hydrolysis of urea into ammonia and carbon dioxide: \[ \text{CO(NH}_2)_2 + \text{H}_2\text{O} \xrightarrow{\text{Urease}} 2\text{NH}_3 + \text{CO}_2 \]
- In the absence of adequate nickel, urease activity is impaired, leading to toxic accumulations of urea in leaf tips and causing necrotic tip burn.
- Molybdenum (Mo) is associated with nitrogenase and nitrate reductase.
- Iron (Fe) is associated with catalase, peroxidase, and cytochromes.
- Cobalt (Co) is essential for cobalamin (Vitamin $\text{B}_{12}$) synthesis in nitrogen-fixing bacteria.

Step 3: Final Answer:
The element associated with urease activity is Nickel (Ni).