Influence Of Drought On Expression Of Camptothecin Biosynthetic Key Enzyme Genes In Camptotheca Acuminata Seedlings

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 biosynthetic pathway as they links primary and secondary metabolism. Effect of drought on camptothecin accumulation and key enzyme genes (TSB and TDC) transcripts in young leaves, mature leaves, and bark of C. acuminata seedlings were studied, and correlations between levels of TSB mRNA, TDC1 mRNA, TDC2 mRNA and CPT content were discussed briefly. The results are as follows.In the first four days of drought treatment, CPT content in young leaves increased, but not at day 2, and then decreased quickly by day 6 to a constant level. In mature leaves and bark, the amount of CPT decreased in response to drought.In seedlings without treatment, TSB was expressed at high levels in all tissues examined. In young leaves, roots, bark and mature leaves, TSB mRNA abundance decreased sequently. TDC1 expressed at high levels only in bark. In mature leaves and roots, it expressed at low levels. The expression of TDC2 was not detected at any tissues in untreated seedlings.In young leaves, TSB expression was induced slightly, and then decreased in response to water deficit. Changes of TSB mRNA abundance in mature leaves in response to drought were not obvious. Bark TSB transcript levels were induced transiently at day 2 after no watering, but there is no correlation between it and soil water content.In young leaves, the level of TDC1 transcripts increased gradually until the soil water content reached 25% and then decreased as the soil water content decreased. The steady-state levels of TDC1 mRNA in mature leaves and bark were transiently induced at day 4 or 5. TDC2 didn't express in all tissues examined until day 8 or 9, when the seedlings had been heavily wilted.