Influence of seasonal and ontogenic parameters on the pattern of key terpenoid indole alkaloids biosynthesized in the leaves of Catharanthus roseus

Abstract

Catharanthus roseus is known for its anticancer bisindole alkaloids, vinblastine and vincristine that are derived from the condensation of monomeric terpenoid indole alkaloids (TIAs), catharanthine and vindoline. The in planta content of TIAs varies with seasons and ontogeny making it difficult for growers to define the optimal parameters for harvesting for specific TIAs. Here, specific leaf TIAs were profiled in the plant at frequent intervals throughout the year covering various seasons under North-Indian conditions. Higher bisindole alkaloid content was observed during summer (June; average day temperature ≥ 40 °C), whereas vindoline content was higher in winter and spring (mid-December to mid-April). Further, the plant was analyzed for variation in ontogenic localization of TIAs in the leaves. The monomeric TIAs were present maximally in the top-level leaf-pairs, whereas the bisindole alkaloids were present maximally in the middle-level leaf-pairs. Analysis of relative abundance of individual TIAs in the total alkaloid pool indicated a clear partitioning between vindoline on one hand and bisindole alkaloids on the other. qRT-PCR-based expression analysis of 10 pathway genes (tdc, str, sgd, t16h, omt, t3o, t3r, nmt, d4h, dat) involved in the biosynthesis of key TIAs, like vindoline, indicated that the transcript abundance of all the genes, except sgd, was significantly higher in winter as compared to summer. Also, upon moving down from the top to the lower level leaf-pairs, the transcript abundance of all the genes decreased significantly. This study defines the seasonal and ontogenic parameters for harvesting of C. roseus leaves for optimal recovery of specific TIAs.