1. Abscisic acid is one of the “classical” 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!).
  2. Abscisic acid was characterized in the early 60s and is named after its role in the process of abscission. Abscission is the shedding of leaves over winter by deciduous plants.
  3. Unlike some other plant hormones, which exist in a myriad of related chemical forms, there is essentially only one abscisic acid (ABA).
  4. Its 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.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. Some plant pathogenic fungi also produce ABA. Perhaps this helps the fungus by suppressing plant defenses.
  10. On the other hand, it is also thought that ABA stimulates the activation of genes important in plant wound responses.