Role of Phytohormones in Plant Responses to Acid Rain

Acid rain (AR) is considered one of the major abiotic hazards to agriculture due to rapid economic and industrial growth worldwide. Acid rain hampers the growth, development, photosynthesis, antioxidant defense, and molecular processes in plants. Plants suffer from oxidative stress under elevated levels of AR exposure because of rate-limiting antioxidant capacity. Acid rain also affects endogenous hormone homeostasis; hence, hormonal supplementation under such circumstances may strengthen plant defense in order to combat the stress generated by environmental threats. Moreover, various signaling molecules and plant growth regulators modulate vital physiological, biochemical, and molecular processes in plants to cope with environmental stresses. In the current book chapter, we highlight that melatonin (an indoleamine low molecular weight molecule), glutathione (free thiol tripeptide), and abscisic acid (isoprenoid plant hormone) act as significant growth regulators, bio-stimulators, and antioxidants to enhance growth, photosynthetic activity, and oxidative stress tolerance by reducing reactive oxygen species (ROS) accumulation under AR stress conditions. However, there is a research need to increase our understanding of the impact of phytohormones on basic life functions and develop new approaches to advance plant cultivation and industrial agriculture in AR conditions.