Role of abscisic acid in plant stress tolerance

The phytohormone abscisic acid (ABA) plays a regulatory role in many physio logical processes in plants. Different stress conditions such as water, dro ught, cold, light, and temperature result in increased amounts of ABA. The action of ABA involves modification of gene expression and analysis of resp onsive promoters revealed several potential cis- and trans-acting regulator y elements. The nature of ABA receptors is unknown. The precise role of ABA under both abiotic and biotic stress conditions, while unclear, is of curr ent interest in many laboratories in the world. Molecular mechanisms underl ying the role of ABA in stress tolerance in plants need to be understood.