Effect of Different Light Qualities on Essential Oil and Asarinin in Asarum heterotropoides Fr. Schmidt var. mandshuricum (Maxim.) Kitag

Asarum heterotropoides Fr. var. mandshuricum (Maxim.) is a perennial herb native to China. Its essential oil components and asarinin are health-promoting compounds. However, cultivation under natural light can affect the growth and secondary metabolite yield of this sciophyte. Adjustment of light irradiance may be beneficial in this respect. Here, we applied six types of filtered solar irradiance by using filter films of red (I), yellow (II), blue (III), green (IV), purple (V) and 50% sunlight (VI). We measured net photosynthetic rate (APn), activity of phenylpropanoid biosynthetic enzymes, asarinin content, and essential oil content and composition. Light quality treatments V and VI resulted in increased APn, enzyme activities, asarinin content and essential oil content. Samples harvested in September 2020 had relatively higher contents and enzyme activities compared to those harvested in July 2020. Elemicin, 2,5-dimethoxytoluene and methyleugenol accumulated at higher levels in response to light quality V. Light qualities III and IV showed promising results for several compounds. Overall, we conclude that controlling the light conditions in growing environments promotes the amount of asarinin and essential oil by regulating photosynthesis and the activities of phenylpropanoid biosynthetic enzymes.