Abscisic Acid is a naturally occuring plant hormone involved in plant growth and stress response. It is produced partially via the mevalonic pathway in
chloroplasts and other plastids. The production of ABA is accentuated by stress, including water loss or freezing temperatures. The activation of ABA can occur by one of two methods: 1) an ABA-glucose ester can form by attachment of glucose to ABA, or 2) the oxidation of ABA can occur to form phaseic acid and dihydrophaseic acid.
The transport of ABA can occur in both xylem and phloem tissues and it can also be translocated through paranchyma cells. Some functions of ABA include: Stimulating the closure of stomata, Inhibition of shoot growth, induction of seeds to synthesize storage proteins, inhibition of the affect of gibberellins, and the induction of gene transcription in response to wounding (especially for proteinase inhibitors).