Cytosolic Ca(2+) and jasmonate mediate signals that induce defense responses in plants. In this study, the interaction between Ca(2+) and methyl jasmonate (MJ) in modulating defense responses was investigated by monitoring ajmalicine production in Catharanthus roseus suspension cultures. C. roseus suspensions were treated with nine combinations of CaCl(2) (3, 23, and 43 mM) and MJ (0, 10, and 100 microM) on day 6 of growth. Increased Ca(2+) influx through the addition of extracellular CaCl(2) suppressed ajmalicine production in MJ-induced cultures. The highest ajmalicine production (4.75 mg/l) was observed when cells were treated with a low level of calcium (3 mM) combined with a high level of MJ (100 microM). In the presence of 3 mM CaCl(2) in the medium, the addition of Ca(2+) chelator EGTA (1, 2.5, and 5 mM) or Ca(2+) channel blocker verapamil (1, 10, and 50 muM) to MJ-induced (100 microM) cultures on day 6 also inhibited ajmalicine production at higher levels of the Ca(2+) inhibitors. Hence, ajmalicine production in MJ-induced C. roseus cultures depended on the intracellular Ca(2+) concentration and a low extracellular Ca(2+) concentration (3 mM) enhanced MJ-induced ajmalicine production.