Which PGR is known for its role in plant responses to biotic and abiotic stresses?

Abscisic acid

The correct answer is Option (3) - Abscisic acid

Plant growth regulators (PGRs) are categorized into two main groups: plant growth promoters and plant growth inhibitors.

Plant growth promoters are responsible for activities that promote growth, including cell division, cell enlargement, pattern formation, tropic growth, flowering, fruiting, and seed formation. There are three major types of plant growth promoters: auxins, gibberellins, and cytokinins.

On the other hand, plant growth inhibitors play essential roles in inducing plant responses to various factors such as wounding, biotic and abiotic stresses, dormancy, and abscission. Abscisic acid is a well-known plant growth inhibitor. Ethylene, while primarily considered a growth inhibitor, also plays a role in certain growth promotion activities.

These two categories of PGRs help regulate and balance plant growth and responses to environmental cues.

In natural environments, plants frequently face a combination of abiotic stresses like drought, salt, heat, or cold, along with biotic stresses from both necrotrophic and biotrophic pathogens. Understanding how plants respond to these stresses and the points where different response pathways intersect is crucial. Calcium sensors are often considered the initial responders to external stimuli, initiating downstream signaling processes. Abscisic acid (ABA) is a key plant hormone that regulates stress responses. It interacts with the jasmonic acid (JA) and salicylic acid (SA) signaling pathways, helping the plant allocate its resources to either mitigate the effects of abiotic stresses or defend against pathogens.