Question

Chlorosis is caused by various factors like
(A) lack of light
(B) Iron Deficiency
(C) Magnesium Deficiency
(D) Excess of Calcium
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only
• B. (A), (B) and (C) only
• C. (B), (C) and (D) only
• D. (A), (B), (C) and (D)

Hint:

When evaluating causes of chlorosis, remember that it can be triggered by multiple pathways:
- Physical factors (lack of light),
- Direct nutritional deficiencies (iron, magnesium), and
- Soil chemistry imbalances (excess calcium causing iron lockouts).
All of these can lead to a reduction in chlorophyll levels.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Chlorosis is a condition where plant leaves produce insufficient chlorophyll, causing them to turn pale green, yellow, or white.
Because chlorophyll is the primary pigment used in photosynthesis, chlorosis can significantly reduce a plant's ability to manufacture carbohydrates and survive.

Step 2: Detailed Explanation:
Let us analyze each of the listed factors to see how they can cause chlorosis:
- (A) Lack of light: Chlorophyll synthesis requires light as a catalyst.
When plants are grown in prolonged darkness, they cannot produce chlorophyll, leading to pale, yellow leaves — a process known as etiolation or light-induced chlorosis.
- (B) Iron Deficiency: Iron is a crucial cofactor for the enzymes involved in the chlorophyll biosynthetic pathway (such as coproporphyrinogen oxidase).
A lack of available iron prevents plants from synthesizing chlorophyll, leading to interveinal chlorosis, where the veins remain green while the surrounding leaf tissue turns yellow.
- (C) Magnesium Deficiency: Magnesium is the central coordinating atom in the chlorin ring of the chlorophyll molecule.
Without sufficient magnesium, plants cannot produce the pigment, leading to chlorosis, which typically starts in the older leaves.
- (D) Excess of Calcium: High calcium levels, especially in calcareous soils with high calcium carbonate content, raise the soil pH.
This alkaline environment causes soluble ferrous iron (\( \text{Fe}^{2+} \)) to oxidize into insoluble ferric forms (\( \text{Fe}^{3+} \)), making it unavailable to plants.
This iron lockout leads to a condition known as "lime-induced chlorosis."
Since all four factors can cause chlorosis through physical, nutritional, or chemical pathways, they are all valid causes.
Therefore, the correct option is (D).

Step 3: Final Answer:
All the listed factors — lack of light, iron deficiency, magnesium deficiency, and excess of calcium — can cause chlorosis, making (A), (B), (C) and (D) the correct option.