Abscisic Acid: Definition, Meaning, Overview, Function

What Is Abscisic Acid In Plants?

Abscisic acid, ABA, is one of the phytohormones that play a vital role in regulating various physiological processes in plants. Sometimes referred to as 'stress hormone' owing to its involvement in plant responses to environmental stresses like drought, cold, and salinity. ABA acts both as an inhibitor of plant growth and as a modulator of abscission and dormancy.

Structure Of Abscisic Acid, Aba

• ABA is a sesquiterpenoid compound with a unique chemical structure.

• It is naturally dextrorotatory (+), and the synthetic ABA is a racemic mixture.

Why Is Abscisic Acid Called A Stress Hormone?

• ABA is considered a stress hormone because its synthesis is induced by various environmental stresses, including drought, water logging, and high salinity.

• It enables the plants to adapt to adverse external conditions by appropriately altering their internal environment.

Functions Of Abscisic Acid (Aba)

• Abscisic acid occupies a center-stage position in many developmental and physiological processes:

• Stomatal Closure: ABA promotes stomatal closure in the event of high salinity and water stress, thus reducing the loss of water through transpiration.ABA combines with other phytohormones—jasmonates, nitric oxide—and signalling molecules to trigger stomatal closure.

• Seed Dormancy: ABA induces dormancy in seeds, making them tolerant to desiccation and other growth-unfavorable conditions, hence facilitating their storage for a longer period.

• Root Growth and Modification: ABA helps in regulating the expression of genes and biosynthesis of lipids and storage proteins involved in maintaining root growth and water uptake under nitrogen deficiency and drought conditions.

• Signal Transduction: ABA is involved in the signal transduction pathway that comes into play in response to stress; ABA interacts in this process with other phytohormones like jasmonates and nitric oxide, which are signalling molecules.

• Dehydration and Osmoprotection: ABA induces the synthesis of dehydrins, osmoprotectants, and protective proteins that confer dehydration tolerance on plants.

• Long-Term Growth: ABA modulates long-term growth by influencing the expression of the stress-responsive genes in plants and controls the capacity of continued adaptation of the plant to stress.

Stress Hormones In Humans

• Stress hormones are those which get secreted during stress and emergency conditions.

• These hormones take on to launch a set of stress reactions, namely the "fight or flight" response.

Stress Hormones In Humans

The three main human stress hormones are:

• Adrenaline: Secreted by the adrenal medulla, it increases the rate of heartbeat, rate of respiration, alertness, dilation of pupils, piloerection, and sweating.

• Noradrenaline: It is also released from the adrenal medulla leads to increased alertness and prepares the body physically for an action.

• Cortisol: Produced by the adrenal cortex, it maintains water balance and blood pressure, has immunosuppressive effects, and leads to the regulation of gluconeogenesis, lipolysis, and proteolysis.

How Do Stress Hormones Work In A Stressful Situation?

Stress hormones induce several reactions to manage stress. They:

• Quick Response: Adrenaline and noradrenaline increase heart rate, breathing rate, arousal, pupil dilation, piloerection, and sweating. It also initiates the hydrolysis of glycogen and raises blood sugar.

• Slow Response: Cortisol slowly responds to the stressful condition. It maintains the balance of water and blood pressure, represses immunological response, and controls gluconeogenesis, lipolysis, and proteolysis.

Conclusion

ABA is a phytohormone involved in the acclimatization of plants under environmental stresses. Taking the role of a signal transducer, regulating stomatal closure, seed dormancy and root growth, ABA plays a very important role in the survival of plants. Students majoring in biology and agriculture would therefore find information on ABA functions and roles very important.

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