Question

The typical earliest symptom of Iron (Fe) deficiency in the crop plant is

• A. Interveinal chlorosis of older leaves
• B. Interveinal chlorosis of young leaves
• C. Necrotic spots on old leaves and fruits
• D. Leaf rosetting and the poor internode elongation

Hint:

To remember nutrient mobility:
Mobile nutrients (N, P, K, Mg) \( \rightarrow \) Deficiency appears first on older leaves.
Immobile nutrients (Fe, Ca, B, S) \( \rightarrow \) Deficiency appears first on younger leaves.
Since iron is immobile and required for chlorophyll, its deficiency causes interveinal chlorosis in young leaves.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Mineral nutrient deficiency symptoms depend on the physiological role of the nutrient and its mobility within the plant's vascular system.
If a nutrient is mobile, the plant can translocate it from older tissues to newer, actively growing tissues, so deficiency symptoms appear first on older leaves.
If a nutrient is immobile, it cannot be remobilized, so deficiency symptoms appear first on young, developing leaves.

Step 2: Detailed Explanation:
Let us analyze the physiological behavior of iron (Fe) in plants:
1. Physiological Role of Iron: Iron is required for chlorophyll biosynthesis, electron transport (as a constituent of cytochromes and ferredoxin), and several enzymatic reactions.
2. Mobility of Iron: Within the plant vascular system, iron is highly immobile.
Once incorporated into structural or metabolic components in mature leaves, it cannot be translocated to newly forming tissues.
3. Deficiency Symptom Development: When iron is deficient, the plant cannot synthesize chlorophyll in newly emerging tissues.
Because the vascular bundles (veins) retain their chlorophyll longer than the surrounding mesophyll cells, the young leaves develop a characteristic pattern of interveinal chlorosis (yellowing between green veins).
Since iron is immobile, this symptom appears first and most severely on the youngest leaves at the shoot apex.
- Interveinal chlorosis of older leaves (A) is typical of magnesium (Mg) deficiency, as magnesium is a highly mobile element.
- Rosetting and poor internode elongation (D) are typical symptoms of zinc (Zn) deficiency, which is caused by a reduction in auxin biosynthesis.

Step 3: Final Answer:
The typical earliest symptom of iron deficiency is interveinal chlorosis of the youngest leaves, corresponding to option (B).