Abstract
Vinblastine (VBL) and vincristine (VCR) are produced exclusively and in small amounts in Catharanthus roseus. These secondary metabolites (terpenoid indole alkaloids) have immense medicinal value. In this study, the impact of different concentrations of salicylic acid (SA), indoleacetic acid (IAA), or tryptophan (TRP) on the biosynthesis of VBL and VCR in C. roseus plants was investigated. Using quantitative real-time PCR, gene expression levels of the transcription factor ORCA3 and expression levels of genes encoding the catalytic enzymes strictosidine synthase (STR), tryptophan decarboxylase (TDC), and desacetoxyvindoline 4-hydroxylase (D4H) were studied. Treatment with 0.5 mg L-1 IAA significantly increased the gene expression of ORCA3, STR, and D4H, compared to the control; however, there was no effect on TDC. Production of VBL and VCR was qualitatively and quantitatively analyzed by HPLC using the corresponding reference standards. The maximum production of VCR and VBL, 146.23 and 311.09 mu g mL(-1), respectively, was achieved with 0.5 mg L-1 IAA. In addition, compared to the control plants, spraying C. roseus plants with 0.5 mg L-1 IAA resulted in the maximum dry weight, maximum content of photosynthetic pigments (Chl a, b and carotenoids), enhanced activity of antioxidant enzymes (catalase, superoxide dismutase, ascorbate peroxidase), and phenylalanine ammonia-lyase. This study demonstrated the concentration-dependent induction effect of IAA in the biosynthesis of VCR and VBL. Therefore, IAA can be used to compensate for the low production of VCR and VBL under natural conditions.