Abscisic acid (ABA) is the primary hormone that mediates plant responses to stresses such as cold, drought, and salinity. Single-cell microinjection experiments in tomato were used to identify possible intermediates involved in ABA signal transduction. Cyclic ADP-ribose (cADPR) was identified as a signaling molecule in the ABA response and Mras shown to exert its effects by way oi calcium. Bioassay experiment is showed that the amounts of cADPR in Arabidopsis thaliana plants increased in response to ABA treatment and before ASA-induced gene expression.