Question

A characteristic symptom of interveinal chlorosis occurring first in the older leaves is due to the deficiency of -
(A)
(B)
(C)
(D)

• A. Potassium
• B. Magnesium
• C. Calcium
• D. Iron

Hint:

Older Leaves + Interveinal Chlorosis = Magnesium (\(Mg\)).
Younger Leaves + Interveinal Chlorosis = Iron (\(Fe\)).
This "Mobile vs. Immobile" logic is the most important concept in plant mineral nutrition questions.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question requires identifying a specific nutrient deficiency based on two diagnostic clues:
1. The type of symptom: Interveinal chlorosis (yellowing between the green veins).
2. The location: Occurring first in older leaves.
Detailed Explanation:

• Role of Magnesium (\(Mg\)):
Magnesium is the central atom of the chlorophyll molecule, essential for photosynthesis.
It also acts as a cofactor for many enzymes involved in phosphate metabolism and protein synthesis.

• Deficiency Logic:
Magnesium is a highly mobile element within the plant.
When the supply is deficient, the plant breaks down chlorophyll in older leaves to mobilize the Magnesium and transport it to the younger, developing leaves (the metabolic sinks).
Because chlorophyll is lost primarily from the tissue between the vascular bundles (veins), the veins remain green while the rest of the leaf turns yellow. This is "interveinal chlorosis."

• Comparison with other elements:
Iron (\(Fe\)): Also causes interveinal chlorosis, but because Iron is immobile, the symptoms appear first in young leaves.
Calcium (\(Ca\)): Immobile; causes tip hook/necrosis in young tissues.
Potassium (\(K\)): Causes marginal chlorosis/necrosis in older leaves, not typically interveinal chlorosis.

Step 2: Final Answer:
Interveinal chlorosis in older leaves is the classic signature of Magnesium deficiency.