Abscisic acid (ABA) is a plant hormone that plays a critical role in various physiological processes related to plant growth, development, and stress responses. It is often referred to as the “stress hormone” because of its involvement in plant responses to environmental stresses. Here are key points about abscisic acid (ABA):

• Drought Response: ABA is perhaps best known for its role in the plant’s response to water stress, particularly drought conditions. When a plant experiences water scarcity, ABA levels in the plant increase. ABA helps the plant conserve water by reducing transpiration (the loss of water vapor through the stomata) and promoting stomatal closure, which limits the loss of water.
• Seed Development and Dormancy: ABA also plays a role in seed development and dormancy. It inhibits germination in seeds, helping them remain dormant until conditions are favorable for growth. When seeds experience sufficient moisture, ABA levels decrease, allowing germination to proceed.
• Stomatal Regulation: ABA regulates the opening and closing of stomata (small openings on leaves and stems) in response to changes in environmental conditions. It helps control gas exchange, water loss, and CO2 uptake, thereby affecting photosynthesis.
• Response to Environmental Stress: ABA is involved in various stress responses, including responses to salinity (high salt levels in the soil), extreme temperatures, and pathogen attacks. It helps plants adapt to and cope with adverse environmental conditions.
• Leaf Senescence: ABA contributes to the regulation of leaf senescence, the aging and eventual death of leaves. It is part of the plant’s mechanism for recycling nutrients from aging leaves back to other parts of the plant.
• Role in Fruit Ripening: ABA can also be involved in fruit ripening, where it influences the breakdown of chlorophyll and the development of pigments and flavors in fruit.
• Commercial Applications: ABA is sometimes used in agriculture and horticulture to control fruit ripening and improve the post-harvest quality of fruits and vegetables.