Effects of exogenous salicylic acid on accumulation of camptothecin and gene expression in Camptotheca acuminata

Camptotheca acuminata Decne (Nyssaceae) is major natural source of camptothecin, an anticancer drug widely used for clinic therapy. Previous works have shown that many plant hormones or elicitors could regulate camptothecin biosynthesis, but few reports have examined sustainable effects of these plant hormones on plants for producing camptothecin. In this work, seedlings obtained from in vitro rapid propagation were used for investigating the sustainable effect of salicylic acid (SA) on transplanted C. acuminata tissues, especially leaves, for camptothecin biosynthesis. Our results indicate that exogenous SA could continuously induce the expression of iridoids pathway genes in C. acuminata leaves for promoting camptothecin production. High expression of iridoids pathway genes still could be observed in bioactive young leaves 180 days after seedlings had been transplanted to soil. In C. acuminata, iridoids pathway genes are expressed at very low levels or are not detectable in old leaves, resulting in decreasing production of camptothecin with leaf development. Interestingly, the expression of these genes could be detected clearly in old leaves of transplanted C. acuminata pretreated with 10 μmol·L –1 of SA during the in vitro rapid propagation phase, which indicates the particular function of SA for a sustainable effect on maintaining relatively high expression levels of iridoids pathway genes for camptothecin biosynthesis.