Plants growing under prolonged water stress condition develop the phenomenon of leaf area adjustment which is

Options

A. Shortening of plastochron
B. Reduction of leaf surface area
C. Shortening of internodal length
D. Shedding of older leaves

Answer

### Step-by-Step Solution:

1. **Understanding Water Stress in Plants**:
- Plants experience water stress when they are subjected to prolonged periods without adequate water supply. This can lead to physiological changes to conserve water.

2. **Phenomenon of Leaf Area Adjustment**:
- Under prolonged water stress, plants undergo a phenomenon known as leaf area adjustment. This involves modifications in the leaf structure to reduce water loss.

3. **Modification of Leaf Structure**:
- To adapt to water stress, plants develop thicker cuticles. A thicker cuticle acts as a barrier to water loss.
- Additionally, plants may develop sunken stomata. Sunken stomata are located in a way that reduces exposure to air, thereby minimizing transpiration.

4. **Role of Abscisic Acid**:
- The hormone abscisic acid (ABA) plays a crucial role during water stress. Its levels increase in response to water scarcity.
- Increased levels of ABA lead to the closure of stomata. Stomatal closure is a critical response that helps to reduce water loss through transpiration.

5. **Reduction in Leaf Surface Area**:
- The adjustments made by the plant, including thickening of the cuticle and stomatal closure, result in a reduction of the leaf surface area.
- A smaller leaf surface area leads to decreased transpiration, which is the process of water loss from the plant.

6. **Survival Under Stress Conditions**:
- By reducing leaf surface area and minimizing water loss, plants can survive longer under conditions of prolonged water stress. This adaptation is crucial for their survival in arid environments.

### Final Conclusion:
The phenomenon of leaf area adjustment in plants under prolonged water stress involves modifications such as thicker cuticles, sunken stomata, increased levels of abscisic acid leading to stomatal closure, and ultimately a reduction in leaf surface area to conserve water.

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