Nitric oxide (NO) mediates a signal pathway that is involved in many defense responses of plants to biotic and abiotic stresses such as the hypersensitive cell death and the activation of defense-related genes. To determine the role of NO in secondary metabolite production of plant cells, sodium nitroprusside (SNP) is utilized as the donor of NO to investigate its effect on the production of terpenoid indole alkaloids of Catharanthus roseus cell suspension cultures. The results showed that the production of ajmalicine, catharanthine, and total alkaloids of C roseus cells treated with 10.0 mmol/L SNP were 20.1, 24.2 and 51.3 mg/L, being 1.6-, 2.9- and 1.8-fold higher than those of untreated cells respectively. SNP-induced terpenoid indole alkaloid production of the cells was blocked by NO specific scavenger 2-4-carboxypheny1-4,4,5,5-tetramethylimidazoline-1-oxyl-3- oxide (CPITO), which indicated that the effects of the application of SNP were caused by NO released from it rather than SNP itself. SNP treatment also induced the activation of protein kinases in C roseus cell cultures. Pretreatment of the cells with protein kinase inhibitor K-252a suppressed SNP-induced terpenoid indole alkaloid production. The results strongly suggested that NO released from SNP triggered terpenoid indole alkaloid biosynthesis of C. roseus cells through a protein kinase-dependent signal pathway. (c) 2005 Elsevier Inc. All rights reserved.