Question

Which one of the following hormones is inducing stomatal closure to avoid the loss of turgor during water deficit in plants?

• A. IBA
• B. IAA
• C. GA
• D. ABA

Hint:

ABA is commonly referred to as the "stress hormone" because of its rapid synthesis in response to environmental stresses like drought, salinity, and cold.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Under water-deficit stress, plants must minimize transpiratiol water loss to maintain leaf turgor and prevent dehydration.
This process is mediated by stress-induced phytohormones that act on guard cells.

Step 2: Detailed Explation:
Abscisic Acid (ABA) is the primary stress hormone in plants:
- When soil moisture is depleted, roots sense the water deficit and synthesize ABA, which is transported through the xylem to the leaves.
- In the guard cells, ABA triggers an efflux of potassium ions (\(K^+\)) and anions, causing water to leave the guard cells by osmosis.
- The loss of turgor in the guard cells causes the stomatal pore to close, reducing transpiration and conserving water.
- In contrast, Indole-3-butyric acid (IBA) and Indole-3-acetic acid (IAA) are auxins involved in rooting and cell elongation, while Gibberellic acid (GA) promotes stem elongation and germition.
Thus, ABA is the hormone responsible for inducing stomatal closure under water-deficit stress.

Step 3: Fil Answer:
Abscisic acid (ABA) is the hormone that induces stomatal closure during water deficit.
Hence, the correct option is (D).