What degree of light deficiency is suitable for saikosaponin accumulation by Bupleurum chinense DC.?

Abstract

Total saikosaponin yield in Bupleurum chinense DC. roots depends on the root biomass production and the saikosaponin content in roots, which are both affected by abiotic factors. Bupleurum chinense is relatively shade-tolerant. To test how total saikosaponin yield responds to light conditions, different light intensities (500, 200, and 50 μmol m−2 s−1) were established in artificial climate incubators. Responses of plant morphological and physiological characteristics and of saikosaponin synthesis to different light intensities were measured to find suitable light conditions for improving total saikosaponin yield. Among these light conditions, moderately low light intensity (MLI, 200 μmol m−2 s−1) produced plants with the highest leaf area, chlorophyll content, effective quantum yield of PSII (ΦPSII), photochemical quenching coefficient (qP), electron transport rate (ETR), maximum carboxylation efficiency (Vcmax), maximum electron transport rate (Jmax), and triose phosphate utilization rate (VTPU), which suggests a well-functioning photosynthetic apparatus capable of fully utilizing the limited light energy. Moreover, the plants had the highest root–shoot ratio, saikosaponin content, and total saikosaponin yield, which indicates that they allocated more resources to storage and defensive adaptations. Under extremely low light intensity (ELI, 50 μmol m−2 s−1), more energy was partitioned to photoprotection, and strong oxidation resistance developed, but saikosaponin accumulation and root biomass were lowest due to greatly reduced carbon assimilation. The MLI improved both the quantity and the quality of herbal extracts from B. chinense: the total saikosaponin yield was 1.3 times the corresponding value of the control (500 μmol m−2 s−1), and lower illumination levels were counterproductive. Our results suggest that B. chinense would be suitable for introducing to an agroforestry system.