Question

Purple orange colour of older leaves is due to the deficiency of

• A. Nitrogen
• B. Phosphorus
• C. Potassium
• D. Calcium

Hint:

Associate the color ______Purple______ directly with ______Phosphorus______ (both start with the letter ______P______).
This purplish pigmentation on older leaves is due to the accumulation of anthocyanin pigments under low-phosphorus stress.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Essential plant nutrients perform specific structural and physiological roles.
When any of these nutrients are deficient, plants exhibit characteristic visual symptoms.
The location of the symptom (older vs. younger leaves) depends on the mobility of the nutrient within the plant vascular system.

Step 2: Detailed Explanation:
Phosphorus (P) is a highly mobile nutrient within the plant.
When a deficiency occurs, the plant translocates phosphorus from older, mature tissues to actively growing younger tissues at the shoot apex.
Therefore, deficiency symptoms of phosphorus appear first on the ______older leaves______.
Physiologically, phosphorus deficiency impairs energy transfer (ATP synthesis) and sugar metabolism.
This metabolic disruption leads to an abnormal accumulation of sugars in the leaves, which triggers the synthesis of anthocyanin pigments.
Anthocyanins produce a highly characteristic dark green color that quickly turns into a distinct ______purple, bronze, or orange-purple coloration______ on the margins and undersides of the older leaves.
In contrast, Nitrogen deficiency causes uniform yellowing (chlorosis) of older leaves.
Potassium deficiency causes marginal burning or scorching of older leaves.
Calcium is immobile, so its deficiency symptoms appear on younger leaves as tip hook or distorted growing tips.

Step 3: Final Answer:
The purple-orange coloration of older leaves is caused by the deficiency of phosphorus, which corresponds to option (B).