Effect of Drought and Nitrogen on Betulin and Oleanolic Acid Accumulation and OSC Gene Expression in White Birch Saplings

摘要

Betulin and oleanolic acid are pentacyclic triterpene compounds with a broad range of biological and medicinal properties. Herein, we demonstrated that 2-year-old white birch saplings were capable of synthesizing betulin and oleanolic acid, and the accumulation of these compounds was significantly affected by seasonal and environmental factors. Indeed, the triterpenes accumulated mainly in the stem bark, with little in the root bark and leaves. From May to October, betulin and oleanolic acid stem bark accumulation displayed an inverted "V" curve, peaking in late July to late August (warmest summer months in Haerbin, China). Interestingly, low nitrogen levels promoted root bark and leaf accumulation of oleanolic acid, while high nitrogen amounts were more favorable to oleanolic acid and betulin accumulation in the stem bark. Moderate and mild drought during the accumulation peak period promoted oleanolic acid and betulin accumulation in the stem bark. Serious shortage of soil moisture inhibited the accumulation of both triterpenes. From July to August, high nitrogen (N3) treatment increased lupeol synthase (BPW) and beta-amyrin synthase (BPY) gene expression in the stem bark. Water stress, especially mild and moderate, induced BPW and BPY expression and downregulated cycloartenol synthase (BPX) in the stem bark. This study provides a strong basis for understanding triterpenoid synthesis in birch at the molecular level.