Exercises
Why is abscisic acid also known as stress hormone?
Abscisic acid (ABA) is called the stress hormone because it plays a central role in mediating plant responses to various abiotic and biotic stresses:
1. Stomatal closure: ABA stimulates the closure of stomata, which reduces water loss through transpiration during conditions of water stress (drought). This is its most well-known stress response.
2. Stress tolerance: ABA increases the tolerance of plants to various kinds of stresses — drought, salinity, cold, and other adverse conditions — by triggering appropriate physiological responses.
3. Seed dormancy: ABA induces and maintains seed dormancy, helping seeds withstand desiccation and other unfavourable environmental conditions until favourable conditions return.
4. General growth inhibition: ABA acts as a general plant growth inhibitor and inhibitor of plant metabolism, slowing down processes when conditions are not suitable for growth.
Because its primary role involves protecting the plant from various stresses (especially water stress via stomatal regulation) rather than promoting growth, ABA is aptly called the stress hormone.
Answer: ABA is called the stress hormone because it stimulates stomatal closure to reduce water loss under drought, increases tolerance to abiotic stresses (drought, salinity, cold), induces seed dormancy to survive unfavourable conditions, and generally inhibits growth and metabolism during stress.