Nitric oxide and reactive oxygen species are two important signal molecules that play key roles in plant defense responses. Nitric oxide generation and oxidative burst and accumulation of reactive oxygen species are the early reactions of Taxus chinensis suspension cells to fungal elicitor prepared from the cell walls of Penicillium citrinum. In order to investigate the relationship and/or interactions of ni- tric oxide and reactive oxygen species in the elici- tor-induced Taxol biosynthesis of T. chinensis sus- pension cells, we treated the cells with nitric oxide specific scavenger 2-4-carboxyphenyl-4,4,5,5-tetra- methylimidazoline-1-oxyl-3-oxide (cPITO), nitric ox- ide synthase inhibitor S,S′-1,3-phenylene-bis(1,2-eth- anediyl)-bis-isothiourea (PBITU), membrane NAD(P) H oxidase inhibitor diphenylene iodonium (DPI), su- peroxide dismutases (SOD) and catalase. The results show that pretreatment of T. chinensis cells with cPITO and DPI inhibited not only the elicitor-induced nitric oxide biosynthesis and oxidative burst, but also the elicitor-induced Taxol production, suggesting that both nitric oxide and reactive oxygen species are involved in elicitor-induced Taxol biosynthesis. Fur- thermore, pretreatment of the cells with cPITO and PBITU suppressed the elicitor-induced oxidative burst, indicating that the oxidative burst might be dependent on NO. Application of nitric oxide via its donor sodium nitroprusside (SNP) triggered Taxol biosynthesis of T. chinensis cells. The nitric ox-ide-induced Taxol production was suppressed by DPI, showing that the oxidative burst is involved in NO-triggered Taxol biosynthesis. However, nitric ox- ide and the fungal elicitor induced Taxol biosynthesis even though the accumulation of reactive oxygen species wass completely abolished in T. chinensis cells. Our data show that nitric oxide may mediate the elicitor-induced Taxol biosynthesis of T. chinensis suspension cells through both reactive oxygen spe- cies-dependent and -independent signal pathways. Moreover, the results of our work show that the elici- tor- and nitric oxide-induced Taxol biosynthesis is inhibited by catalase, indicating that H2O2 from the oxidative burst might be the signal molecule involved in induced Taxol production of T. chinensis cells. Nitric oxide and reactive oxygen species are two important signal molecules that play key roles in plant defense responses. Nitric oxide generation and oxidative burst and accumulation of reactive oxygen species are the early reactions of Taxus chinensis suspension cells to fungal elicitor prepared from the cell walls of Penicillium citrinum. In order to investigate the relationship and / or interactions of ni- tric oxide and reactive oxygen species in the elici- tor-induced Taxol biosynthesis of T. chinensis sus- pension cells, we treated the cells with nitric oxide specific scavenger 2 -4-carboxyphenyl-4,4,5,5-tetra- methylimidazoline-1-oxyl-3-oxide (cPITO), nitric ox- ide synthase inhibitor S, The results show that pretreatment of T. chinensis cells with cPITO and p-hydroxy-isothiourea (PBITU), membrane NAD (P) H oxidase inhibitor diphenylene iodonium (DPI), superoxide dismutases DPI enabled not only the elicitor-induced nitric o xide biosynthesis and oxidative burst, but also the elicitor-induced Taxol production, suggesting that both nitric oxide and reactive oxygen species are involved in elicitor-induced Taxol biosynthesis. Fur- thermore, pretreatment of the cells with cPITO and PBITU suppressed the elicitor-induced oxidative burst, indicating that the oxidative burst might be dependent on NO. Application of nitric oxide via its donor sodium nitroprusside (SNP) triggered Taxol biosynthesis of T. chinensis cells. The nitric ox-ide-induced Taxol production was suppressed by DPI, showing that the oxidative burst is involved in NO-triggered Taxol biosynthesis. However, nitric ox ide and the fungal elicitor induced Taxol biosynthesis even though the accumulation of reactive oxygen species wass completely abolished in T. chinensis cells. Our data show that nitric oxide may mediate the elicitor-induced Taxol biosynthesis of T. chinensis suspension cells through both reactive oxygen spe-cies-dependent and -indepe ndent signal pathways. Moreover, the results of our work show that the elici- tor- and nitric oxide-induced Taxol biosynthesis is inhibited by catalase, indicating that H2O2 from the oxidative burst might be the signal molecule involved in induced Taxol production of T. chinensis cells.