Question

Which of the following is not true about potassium nutrition in plants ?

• A. Potassium plays an important role in formation of starch and translocation of sugar.
• B. Potassium activates number of enzymes in plant.
• C. Potassium is involved in opening and closing of stomata in plant.
• D. Potassium is the main constituents of protein and chlorophyll in plant.

Hint:

Potassium is often called the "regulatory element" or "traffic cop" of plants because it is highly mobile and regulates physiological processes (osmosis, enzyme activation, stomatal movement) without being incorporated into any permanent structural compound.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Potassium (\(K^{+}\)) is a primary macronutrient that, unlike nitrogen and phosphorus, does not form a structural component of organic compounds in plants.
Instead, it exists primarily as a free ion in cell sap, regulating osmotic potential and enzymatic activity.

Step 2: Detailed Explanation:
Let us analyze each statement to identify the incorrect one:
- Statement (A): Potassium is highly involved in carbohydrate metabolism.
It promotes the synthesis of starch and facilitates the loading and translocation of sugars (sucrose) from source leaves to sink organs (tubers, roots, and grains), making this statement true.
- Statement (B): Potassium acts as a vital cofactor and activator for over 60 different plant enzymes involved in respiration, photosynthesis, and protein synthesis, making this statement true.
- Statement (C): Potassium regulates the turgor pressure of guard cells surrounding the stomata.
The active transport of \(K^{+}\) ions into guard cells causes water to enter via osmosis, opening the stomata, while its efflux leads to closure, making this statement true.
- Statement (D): Nitrogen, sulfur, carbon, hydrogen, and oxygen are the main structural constituents of proteins, while magnesium forms the central atom of the chlorophyll molecule.
Potassium does not enter into the chemical structure of proteins or chlorophyll, making this statement false.
Therefore, Statement (D) is not true regarding potassium nutrition.

Step 3: Final Answer:
The incorrect statement is Option D.