Abscisic acid – Definition & Detailed Explanation – Botanical Glossary

I. What is Abscisic Acid?

Abscisic acid (ABA) is a plant hormone that plays a crucial role in regulating various physiological processes in plants. It is a sesquiterpenoid compound that was first discovered in the 1960s and has since been extensively studied for its effects on plant growth and development. ABA is synthesized in various plant tissues, including leaves, roots, and seeds, and is involved in responses to environmental stresses such as drought, salinity, and cold temperatures.

II. What are the Functions of Abscisic Acid in Plants?

Abscisic acid has a wide range of functions in plants, including regulating seed dormancy and germination, stomatal closure, and responses to environmental stresses. ABA is also involved in the regulation of plant growth and development, including leaf senescence, root growth, and fruit ripening. Additionally, ABA plays a role in mediating plant responses to biotic stresses such as pathogen attack and herbivory. Overall, ABA acts as a key signaling molecule that helps plants adapt to changing environmental conditions.

III. How is Abscisic Acid Synthesized in Plants?

Abscisic acid is synthesized through a complex pathway that involves several enzymatic reactions. The precursor for ABA biosynthesis is a carotenoid compound called zeaxanthin, which is converted into ABA through a series of enzymatic steps. The key enzymes involved in ABA biosynthesis include 9-cis-epoxycarotenoid dioxygenase (NCED) and abscisic aldehyde oxidase (AAO). ABA synthesis is tightly regulated by environmental cues such as water availability and light intensity, which influence the expression of genes encoding ABA biosynthetic enzymes.

IV. What are the Effects of Abscisic Acid on Plant Growth and Development?

Abscisic acid has diverse effects on plant growth and development, depending on the concentration and timing of its application. At low concentrations, ABA promotes seed dormancy and inhibits seed germination, while at higher concentrations, it induces stomatal closure and reduces transpiration. ABA also regulates root growth by inhibiting cell division and elongation in the root tip. Additionally, ABA plays a role in leaf senescence and fruit ripening by promoting the breakdown of chlorophyll and the synthesis of ethylene, respectively.

V. How is Abscisic Acid Involved in Plant Responses to Stress?

Abscisic acid plays a crucial role in mediating plant responses to environmental stresses such as drought, salinity, and cold temperatures. In response to water deficit, ABA accumulates in plant tissues and triggers stomatal closure to reduce water loss through transpiration. ABA also regulates the expression of stress-responsive genes that help plants cope with adverse conditions. In addition, ABA promotes the accumulation of osmoprotectants such as proline and sugars, which help plants maintain cellular turgor and survive under stress.

VI. What are the Practical Applications of Abscisic Acid in Agriculture and Horticulture?

Abscisic acid has several practical applications in agriculture and horticulture, including improving crop yield and quality under stressful conditions. ABA can be used as a foliar spray to enhance drought tolerance in crops such as maize, wheat, and rice. By promoting stomatal closure and reducing water loss, ABA helps plants conserve water and maintain photosynthetic activity during periods of water scarcity. ABA can also be applied to promote fruit ripening and improve post-harvest shelf life in fruits such as tomatoes and bananas. Overall, the use of ABA in agriculture and horticulture offers a promising strategy for enhancing plant productivity and resilience to environmental stresses.