In plant biology, abscisic acid (ABA) is one of the main five classes of plant hormones (the others being auxins, cytokinins, gibberellins, and ethylene). It is an inhibitory hormone in plants that helps a plant adapt to stress. So, unlike other plant hormones, it's not beneficial as an additive.

While not widely sold as a plant additive, it's still important to be aware of ABA, just in case you do come across it in a product's ingredient list. Here are the top 10 things you should know about abscisic acid and its role in horticulture.

Abscisic Acid Does Not Mean Much in Terms of Ph

Abscisic acid is one of the main classes of plant hormones, and although it is an acid, its role in plants is not directly related to regulating pH. It’s more complicated than that (of course!).

Abscisic Acid is Named After What it Does

Abscisic acid was characterized in the early 1960s and is named after its role in the process of abscission. Abscission is the shedding of leaves over winter by deciduous plants.

Abscisic Acid is a Family of One

Unlike some other plant hormones, which exist in a myriad of related chemical forms, there is essentially only one abscisic acid (ABA).

Abscisic Acid Has Many Functions in Plants

Abscisic acid's effects on plant growth and development are many, including regulation of the opening and closing of stomata, stimulation or inhibition of root development, dormancy of buds and seeds, protection from dehydration, and many others.

It Starts at the Roots

Abscisic acid is part of the apical dominance system. As auxin moves down from the plant apex, ABA moves up from the roots to work in synergy to maintain the dormancy of lateral buds.

Abscisic Acid Helps Plants Deal with Stress

Sometimes called the stress hormone, ABA is involved in many plant responses to unfavorable conditions such as drought, extreme cold, high soil salinity, and others.

Abscisic Acid Does Not Play Well with Others

Abscisic acid is also known for its “anti” effects in relation to other hormones. For example, auxin inhibits abscission, ABA promotes it; gibberellins promote elongation, ABA inhibits it.

Abscisic Acid Keeps Plants Tough

Stomata close to limit transpiration when ABA binds to receptors on stomatal guard cells, triggering a cascade of events leading to loss of guard cell turgor.

Fungi Make Use of Abscisic Acid, Too!

Some plant pathogenic fungi also produce ABA. Perhaps this helps the fungus by suppressing plant defenses.

Abscisic Acid May Help Plants Heal Themselves

On the other hand, it is also thought that ABA stimulates the activation of genes important in plant wound responses.