Triterpenoid saponins in Aralia elata subjected to combined nutrient availability and light quality

Abstract

Combined light spectra and nitrogen (N) availability may modify contents of triterpenoid saponins (TSs) in leaves of Aralia elata (Miq.) Seem. In this study, A. elata seedlings were raised under light-emitting diode spectra in red- (26.6% red, 59.9% green, and 13.5% blue) and green-colours (12.6% red, 84.6% green, and 2.9% blue) both at a photosynthetic photon flux density of about 77.4 µmol m-2 s-1. N availability was employed at low and high rates of 30 and 90 mg kg-1, respectively. Aralosides-A and -VI did not show any responses to either light or N treatments (ranges of 1.98‒3.75 mg g-1 and 0.21‒1.41 mg g-1, respectively). Compared to the green light, the red light resulted in greater growth but lower foliar N assimilation and aralosides-B (~0.7 mg g-1) and -V concentrations (~16 mg kg-1). The high N availability resulted in greater growth, biomass, foliar chlorophyl and protein concentrations but lower N assimilation and TS concentrations. We conclude that araloside B can be taken as an objective TS harvested in A. elata food-used leaves as a bioactive compound that can be adjusted by light and N manipulations.