Effect Of Shading On Camptothecin Biosynthetic Key Enzymes TSB And TDC

Camptothecin (CPT) is an anti-cancer terpenoid indole alkaloid in Camptotheca acuminata. Tryptophan synthase (TSB) and tryptophan decarboxylase (TDC) are two key enzymes in camptothecin biosynthesis as they link primary and secondary metabolism. Effect of shading on camptothecin accumulation and key enzyme activities (TSB and TDC) in young leaves, mature leaves, bark and root of C. acuminata seedlings were studied, and correlations between activities of TSB, TDC and CPT content were discussed briefly. The results are as follows.(1) CPT content was increased by light shading (60% full sun light) and heavy shading (30% full sun light), CPT content of heavy shading was higher than that of light shading.(2) In seedlings without treatment, TSB activity had no difference in all examined tissues; TDC activity was highest in young leaves, the following were mature leaves, root and bark sequently.(3) During the period of shading, TSB activity firstly decreased, and then increased. In young leaves, mature leaves and bark, TSB activity of heavy shading was higher than that of light shading, however, in root, a reverse result was showed. TDC activity showed a similar regulation as TSB under shading treatment, whereas, no remarkable difference was displayed between light and heavy treatments.(4) In young leaves, mature leaves and bark, there was no obvious correlation between TSB activity, TDC activity and CPT content. In root, there were some correlations between TSB activity, TDC activity and CPT content, especially, the correlation was more obvious between TSB activity and CPT content in light shading.