Abscisic acid (ABA) is an important plant hormone and one of the plant growth regulators. It is mainly involved in the response and regulation of plants to adversity. When abscisic acid was first discovered, it was mistakenly thought to be related to the falling of plant leaves and fruits. However, it is now known that ABA may not have a direct effect on the falling of plant leaves and fruits. It only causes premature aging of organ cells, and then stimulates the increase in ethylene production to cause shedding. The real initiator of the shedding process is ethylene rather than ABA. So let’s get to know abscisic acid together today!
What is abscisic acid?
Abscisic acid is an organic substance with a chemical formula of C15H20O4. It is a plant hormone that inhibits growth. It is named because it can cause leaves to fall off and is widely distributed in higher plants. In addition to causing leaves to fall off, it has other effects, such as causing buds to enter a dormant state and causing potatoes to form tubers. It also has an inhibitory effect on cell elongation. In 1965, it was confirmed that abscisic acid II and dormancy are the same substance, and they were uniformly named abscisic acid.
History of the discovery of abscisic acid
In 1961, W.C. Liu and H.R. Kearns isolated a substance crystal from mature cotton bolls that can accelerate the shedding of petioles after the explant leaves are removed, called “abscisic acid I”, but its chemical structure was not identified.
In 1963, Kazuhiko Ohkuma and F.T. Addicott et al. isolated another substance crystal that accelerates shedding from young cotton bolls, called abscisic acid II. In the same year, C.F. Eagles and P.F. Welling used chromatography to isolate an inhibitory substance from Eurasian maple leaves that can make growing seedlings and buds dormant, and they named it dormancy.
In 1965, Welling et al. compared the chemical properties of dormancy and abscisic acid II and proved that the two are the same substance, and the molecular formula is consistent with that proposed by Kazuhiko Ohkuma et al. in 1965. It is uniformly named abscisic acid. It is widely found in plants.
Hysical and chemical properties of abscisic acid
Abscisic acid is a 15-carbon sesquiterpene compound. Naturally occurring abscisic acid is a corresponding structure, especially the right-handed compound (S)-ABA. The physiological activity of (R)-ABA is the same as that of (S)-ABA in most cases. Its physiological activity depends on the following conditions:
- There is a free carboxyl group,
- There is a double bond at the α- or β-position on the cyclohexane ring,
- The double bond at C-2 is cis.
Experts have found that the natural abscisic acid of plants is a white crystalline powder, which is easily soluble in methanol, ethanol, acetone, chloroform, ethyl acetate and chloroform, etc., and is difficult to dissolve in ether, benzene, etc., with a water solubility of 3-5 g/L (20℃). Abscisic acid has good stability. After being placed at room temperature for two years, the content of active ingredients remains basically unchanged, but it should be sealed and stored in a dry, cool and dark place. The aqueous solution of abscisic acid is sensitive to light and is a strong light-decomposable compound.
Application of abscisic acid
Natural abscisic acid is listed as one of the five major plant hormones along with auxin, ethylene, gibberellin, and cytokinin, and plays an important role in plant growth.
(1) Inhibit growth and improve drought and cold resistance
ABA is a strong growth inhibitor that can inhibit the growth of the whole plant or isolated organs. The effect of ABA on growth is opposite to that of IAA, GA, and CTK. It inhibits cell division and elongation. It inhibits the elongation growth of organs such as coleoptiles, twigs, roots, and hypocotyls. At the same time, it can also induce plants to develop resistance to drought, cold, salt and other adversities by inhibiting growth. It is of great value for the development and utilization of medium and low-yield fields, afforestation, and greening of deserts.
(2) Inhibit seed germination
The accumulation of ABA after seed maturity can induce seeds to enter a dormant state, which is beneficial to the survival of seeds in non-growing seasons or under adverse conditions. It is also an effective inhibitor of seed germination, so it can be used for seed storage to ensure the storage quality of seeds and fruits.
(3) Regulating stomatal closure ABA can also cause rapid closure of leaf stomata.
There are two signal transduction pathways for ABA to regulate stomatal closure: promoting stomatal closure and inhibiting stomatal opening. Under water-deficient conditions, the ABA content in plant leaves increases, causing stomatal closure. This is because ABA promotes the outflow of potassium ions, chloride ions, and malate ions, which promotes stomatal closure. Spraying plant leaves with ABA aqueous solution can close stomata and reduce transpiration rate. Therefore, ABA can be used as an anti-transpiration agent. ABA inhibits the action of potassium ions and proton pumps, thereby inhibiting stomatal opening. ABA can be used to preserve flowers, regulate flowering period, promote rooting, etc., which has great application value in flower gardening.
(4) Inducing and improving stress resistance
Generally speaking, adversities such as drought, cold, high temperature, salinity, and waterlogging can rapidly increase ABA in plants and enhance stress resistance.
For example, ABA can significantly reduce the damage of high temperature to the ultrastructure of chloroplasts and increase the thermal stability of chloroplasts; ABA can induce the resynthesis of certain enzymes to increase the cold resistance, waterlogging resistance, and salt resistance of plants. Therefore, ABA is called stress hormone or stress hormone. The study of ABA and its response genes can reveal the molecular process of plant stress resistance physiological response, thus laying the foundation for the targeted enhancement of crop adaptability to the environment.
Abscisic acid has broad application prospects in agricultural production and can generate huge economic and social benefits. Because the optical configuration of natural abscisic acid in plants is only (+)-cis, trans-ABA, the traditional chemical synthesis method has extremely high production costs, so currently only developed countries such as Japan and the United States are used in large-scale agricultural production
Abscisic acid and S-inducing factor
Abscisic acid is actually S-inducing factor, which is a natural plant hormone produced artificially. At present, there are two manufacturers in the world that use similar microorganisms and different fermentation methods to industrially produce natural abscisic acid, Botrytis cinerea liquid fermentation and Botrytis cinerea continuous plate solid fermentation.
S-inducing factor: New physiological effects have been discovered. Including inducing drought resistance, cold resistance, frost resistance, salt and alkali resistance, and promoting rooting. Also known as the “growth balance factor” of plants
S-inducer is a key factor in balancing the metabolism of plant endogenous hormones and related growth-active substances. It has the ability to promote the balanced absorption of water and fertilizer by plants and coordinate metabolism in the body. It can effectively regulate the root/crown and vegetative growth and reproductive growth of plants, and plays an important role in improving the quality and yield of crops.
S-inducer is also the “stress resistance induction factor” of plants
S-inducer is the “first messenger” that starts the expression of stress resistance genes in plants, and can effectively activate the stress resistance immune system in plants. It has the ability to strengthen the source and enhance the comprehensive resistance of plants (drought resistance, heat resistance, cold resistance, disease resistance, salt and alkali resistance, etc.). It plays an important role in drought resistance and water conservation, disaster reduction and production protection, and ecological environment restoration in agricultural production.
S-inducer is a green and environmentally friendly product
S-inducer is a pure natural product contained in all green plants. The product is obtained through microbial fermentation with high purity and high growth activity; it is non-toxic and non-irritating to humans and animals. It is a new type of efficient and natural green plant growth active substance.
Precautions for using abscisic acid
- When using abscisic acid, the growth stage and type of the plant need to be considered, because different plants and growth stages may react differently to abscisic acid.
- The use of abscisic acid needs to be carried out under the guidance of professionals, and excessive use may have an adverse effect on plant growth.
- Abscisic acid cannot replace the effects of other growth regulators, so when using abscisic acid, the balance of other growth regulators needs to be considered.
Therefore, in the rational use of hormones, we advocate scientific compatibility, and apply them reasonably according to factors such as crop types, soil conditions, and growth cycles to avoid hazards such as reduced yields or total crop failures caused by blind fertilization. Let us work together to apply fertilizers scientifically and use drugs rationally to protect our food safety and soil environment!
