Which of the following is the latest addition to the list of essential nutrients?
Show Hint
Nickel (\(Ni\)) is the \(17^{\text{th}}\) and most recently added essential plant nutrient. It is required in very small amounts (micro/trace element) primarily for the activation of the urease enzyme.
Step 1: Understanding the Concept:
For an element to be classified as an essential plant nutrient, it must meet Arnon and Stout's criteria of essentiality (1939):
The plant cannot complete its life cycle in the absence of the element.
The element's function cannot be replaced by any other element.
The element must be directly involved in the plant's metabolism. Step 2: Detailed Explanation:
Let us review the history of the discovery of essential plant nutrients:
- For many years, the list of essential nutrients remained fixed at 16 elements (C, H, O, N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Mo, Cl).
- Chlorine (\(Cl\)) was established as essential by Broyer et al. in 195
- Nickel (\(Ni\)) was established as the 17th essential element by researchers P. H. Brown, R. M. Welch, and E. E. Cary in 198
- They demonstrated that nickel is a crucial component of the enzyme urease, which catalyzes the conversion of urea into carbon dioxide and ammonia.
- In the absence of nickel, plants accumulate toxic levels of urea in their leaves, leading to necrotic spots.
- In 2004, the Association of American Plant Food Control Officials (AAPFCO) officially added nickel to the list of essential plant elements.
- Let us evaluate other options: Selenium (\(Se\)) and Cobalt (\(Co\)): Are beneficial elements for some plant species but are not classified as universally essential for all higher plants. Step 3: Final Answer:
The correct option is (D).
