New generation plant growth regulators (PGRs) refer to a group of naturally occurring or synthetic compounds, distinct from the five classical plant hormones (auxins, gibberellins, cytokinins, ethylene, abscisic acid), that play crucial roles in regulating plant growth, development, and especially, stress responses. They are often involved in complex signaling pathways and help plants adapt to challenging environmental conditions.

Different New Generation Plant Growth Regulators:

1. Brassinosteroids (BRs): Steroidal hormones found in all plant tissues.

2. Jasmonates (JAs): Lipid-derived signaling molecules.

3. Salicylic Acid (SA): A phenolic compound.

4. Polyamines (PAs): Low molecular weight aliphatic amines (e.g., putrescine, spermidine, spermine).

5. Strigolactones (SLs): Carotenoid-derived lactones.

Role in Mitigating Abiotic Stresses:
These new generation PGRs play significant roles in enhancing plant tolerance to abiotic stresses (e.g., drought, salinity, heat, cold, heavy metals):

• Brassinosteroids (BRs): Exogenous application can significantly enhance plant growth and photosynthesis under stress. They improve membrane stability, activate antioxidant defense systems, and regulate stomatal movement, helping plants withstand drought, salinity, and extreme temperatures. BRs are crucial in maintaining cellular homeostasis under adverse conditions.

• Jasmonates (JAs): Primarily known for their role in defense against biotic stress, JAs also confer tolerance to abiotic stress. They induce the expression of stress-responsive genes, regulate stomatal closure to reduce water loss during drought, and play a role in nutrient uptake under stress conditions.

• Salicylic Acid (SA): SA acts as a key signaling molecule that boosts the plant's antioxidant defense machinery, reducing oxidative damage caused by various stresses. It enhances thermotolerance (heat stress tolerance) and modulates physiological processes to cope with drought and heavy metal toxicity.

• Polyamines (PAs): These act as osmolytes, helping in osmotic adjustment and maintaining cell turgor under drought and salinity stress. PAs stabilize cell membranes and protect macromolecules (proteins, nucleic acids) from damage under various abiotic stresses, functioning as essential stress protectants.

• Strigolactones (SLs): While more recently discovered, SLs are known to modulate root architecture, enhancing nutrient and water acquisition efficiency, which is vital for stress resilience. They also play roles in plant architecture under nutrient deprivation.

These new generation PGRs are crucial for developing stress-tolerant crop varieties and for sustainable agriculture in a changing climate.