Abscisic acid is known as:
Abscisic acid designated as stress hormone and growth inhibitor originates from carotenoid pathway, cleavage of 9 cis violaxanthin and neoxanthin by NCED dioxygenase to xanthoxin then converted by ABA2 short chain dehydrogenase and AAO3 aldehyde oxidase to ABA. Under drought salinity cold endogenous levels rise sharply triggering PYR PYL RCAR receptor family that sequesters PP2C phosphatases ABI1 ABI2 releasing SnRK2 kinases OST1 to phosphorylate targets including bZIP transcription factor ABI5 inducing late embryogenesis abundant LEA genes, anion channel SLAC1 causing stomatal closure reducing transpiration, and enzymes for osmolyte synthesis proline betaine. ABA antagonizes gibberellin by stabilizing DELLA repressors enforcing dormancy and preventing precocious germination vivipary. In tissue culture ABA 1-10 micromolar improves somatic embryo quality preventing secondary embryogenesis, induces desiccation tolerance for synthetic seed storage, synchronizes maturation and enhances acclimatization by promoting cuticular wax deposition. Catabolism via CYP707A hydroxylases maintains homeostasis fine tuning stress response and developmental transitions crucial for embryo physiology.
Ref: Cutler et al., Annu Rev Plant Biol 2010 ABA signaling; NCBI NBK541119 ABA.