title: Ecologically relevant UV-B dose combined with high PAR intensity distinctly affect plant growth and accumulation of secondary metabolites in leaves of Centella asiatica L. Urban.
abstract: We investigated the effects of environmentally relevant dose of ultraviolet (UV)-B and photosynthetic active radiation (PAR) on saponin accumulation in leaves on the example of Centella asiatica L. Urban. For this purpose, plants were exposed to one of four light regimes i.e., two PAR intensities with or without UV-B radiation. The experiment was conducted in technically complex sun simulators under almost natural irradiance and climatic conditions. As observed, UV-B radiation increased herb and leaf production as well as the content of epidermal flavonols, which was monitored by non-destructive fluorescence measurements. Specific fluorescence indices also indicate an increase in the content of anthocyanins under high PAR; this increase was likewise observed for the saponin concentrations. In contrast, UV-B radiation had no distinct effects on saponin and sapogenin concentrations. Our findings suggest that besides flavonoids, also saponins were accumulated under high PAR protecting the plant from oxidative damage. Furthermore, glycosylation of sapogenins seems to be important either for the protective function and/or for compartmentalization of the compounds. Moreover, our study revealed that younger leaves contain higher amounts of saponins, while in older leaves the sapogenins were the most abundant constituents. Concluding, our results proof that ambient dose of UV-B and high PAR intensity distinctly affect the accumulation of flavonoids and saponins, enabling the plant tissue to adapt to the light conditions.
authors.affiliation: Institute of Crop Science and Resource Conservation - Horticultural Science, University of Bonn, Auf dem Hügel 6, 53121 Bonn, Germany.
authors.forename: Viola
authors.initials: V
authors.lastname: Müller
authors.forename: Andreas
authors.initials: A
authors.lastname: Albert
authors.forename: J
authors.initials: J
authors.lastname: Barbro Winkler
authors.forename: Christa
authors.initials: C
authors.lastname: Lankes
authors.forename: Georg
authors.initials: G
authors.lastname: Noga
authors.forename: Mauricio
authors.initials: M
authors.lastname: Hunsche
mesh_terms: D028041:Centella / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D055669:Ecological and Environmental Phenomena; D006027:Glycosides / Q000378:metabolism; D010788:Photosynthesis / Q000528:radiation effects*; D018515:Plant Leaves / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D006027:Glycosides
keywords: Flavonoid; Fluorescence measurements; Light intensity; Oxidative stress; Saponin; Spectral quality