It is also called dormin, or abscisin II. Chemically it is a sesquiterpene (C15H20O4), synthesized from neoxanthin and violaxanthin.

ABA synthesis takes place in the plastids and shares process steps with those of other isoprenoids, such as gibberellins. Neoxanthin and violaxanthin (and antheraxanthin), through a series of reactions, give rise to xanthosine, which when oxidized produces ABA.

The ABA carries out different functions in the plant. The main one is the induction of stomatal closure due to water stress. ABA induces the closing of stomata, reducing plant transpiration and stimulating the synthesis of proteins that help in drought stress resistance. ABA can be synthesized in the root and distributed by the xylem when it detects water deficiency, preparing the plant before the symptoms reach the leaves.

It also intervenes in the response to wounds, inducing the synthesis of protease inhibitors preventing infections.

Additionally, ABA induces bud dormancy, controls seed’s embryonic development, stimulates the synthesis of storage proteins and inhibits germination. It also inhibits vegetative development.

For example, before a water deficit, ABA inhibits plant growth, acting on the extensibility of the cell wall.

Finally, ABA´s function which gives rise to its name, is the abscission of leaves and fruits through the induction of ethylene synthesis.

ABA’s mode of action is still not determined, but its response is mediated through the inhibition of the expression of certain genes.

From an agricultural point of view, ABA is applied in order to improve the plant’s tolerance against water stress, but its sensitivity to UV radiation limits its application. It is also used to accelerate the de-greening of non-climacteric fruits and to prevent apical rot in tomatoes.