Catharanthus roseus L. is an important medicinal plant producing several terpenoid indole alkaloids (TIAs) such as vincristine and vinblastine secondary metabolites with anticancer activity. The TIAs biosynthetic pathways are affected by biotic and abiotic stresses. In this study the effect of drought (7 days), salinity (150 mM NaCl), foliar spray of salicylic acid (10-5 M) and salicylic acid in combination with drought and salinity were investigated separately on the expression of

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... -doline-4-hydroxylase D4H and deacetylvindoline 4-O-acetyl transferase DAT, two late vincristine and vinblastine biosynthetic pathway genes. RNA samples were extracted from leaves and cDNAs were synthesized from all samples and used for analysis in Real time PCR. Data analysis based on Ct curves showed that the expression of these genes increased by the application of abiotic stresses. The maximum increases in the mRNA levels of D4H and DAT genes (537% and 440%, respectively) were noted in plants exposed to drought stress in comparison to the control condition. Also, the results showed that the effects of salinity, drought + salicylic acid and salinity + sali-cylic acid stresses were positive on the increase of D4H and DAT genes expression in comparison to the control plants. Salicylic acid treatment caused a slightly higher gene expression than in control and other treatments. Therefore, it can be concluded that the application of abiotic stresses has a significant role in increasing the expression of genes involved in the biosynthetic pathway of vincristine and vinblastine alkaloids.