Influence of Filtered and Unfiltered Solar Radiation on the Growth Pattern and Secondary Metabolite Synthesis in Catharanthus roseus (L.) G. Don - A Preliminary Study

Abstract

Catharanthus roseus (L.) G. Don is an important medicinal plant known for the production of biologically active indole alkaloids and other secondary metabolites. This preliminary study evaluated the influence of different solar-radiation regimes on plant growth, epicuticular wax accumulation and vincristine content in C. roseus. Seedlings were grown for 50 days under three light environments: ambient high solar radiation, ambient low solar radiation produced by 40-50% light filtration, and UV-B-filtered solar radiation. Growth responses were assessed using shoot length, leaf area, fresh weight and dry weight, while epicuticular waxes and alkaloids were analysed using spectrophotometric, thin-layer chromatographic and high-performance liquid chromatographic methods. Plants grown under filtered radiation showed improved vegetative growth compared with plants exposed to ambient high solar radiation. In contrast, open daylight conditions were associated with earlier flowering. Total epicuticular wax content was highest under ambient high solar radiation, with values of 345.6 +/- 28 ug/g fresh weight, followed by ambient low solar radiation at 309.6 +/- 42 ug/g fresh weight and UV-B-filtered radiation at 291.6 +/- 32 ug/g fresh weight. Wax-class analysis indicated variation in free fatty acids, primary alcohols, secondary alcohols, aldehydes, beta-diketones, wax monoesters and alkanes among treatments. HPLC analysis detected vincristine in leaf extracts from all three light environments. Vincristine content was 820.4 +/- 18 ug/g leaf dry weight under ambient high solar radiation, 830.4 +/- 32 ug/g leaf dry weight under ambient low solar radiation and 316.2 +/- 27 ug/g leaf dry weight under UV-B-filtered radiation. These findings suggest that light quality and quantity influence growth and secondary metabolite accumulation in C. roseus, with UV-B exclusion reducing vincristine accumulation under the conditions of this study.