Effects of Different Stress Treatments on the Total Terpene Trilactone Content and Expression Levels of Key Genes in Ginkgo biloba Leaves

As unique secondary metabolites of Ginkgo biloba L. and relics of Ginkgoaceae, terpene trilactones (TTLs) possess great medicinal value. In this study, we investigated the effects of ultraviolet (UV) irradiation, cold stress (4 °C), and exogenous hormone treatment on TTLs and key genes expression in ginkgo leaves in annual potted ginkgo seedlings subjected to different stress treatments. The processing conditions were as follows: UV treatment (1500 μJ/m2) for 0, 8, 16, 24, and 48 h; cold stress at 4 °C, 400 µmol photons m−2 s−1; 100 μM abscisic acid (ABA); 100 μM methyl jasmonate (MeJA); 10 mM salicylic acid (SA); and 10 mM ethephon (ETH) treatments for 0, 2, 4, 6, and 8 days. Results of evaporative light-scattering detector–high-performance liquid chromatography showed that UV, cold stress, ABA, SA, MeJA, and ETH treatments increased the TTL content at various levels and up to 21.9%. The relationships among the expression levels of the key enzyme genes GbDXS, GbGGPPS, GbLPS, and GbMVD in the TTL biosynthesis pathway were also analyzed. Changes in the TTL content and expression levels of the key genes were significantly and positively correlated with TTL content. UV, cold stress, ABA, SA, MeJA, and ETH were found to increase the TTL content by upregulating the expression of the key genes. This study aimed to reveal the molecular mechanism through which TTLs are synthesized. The results can also provide theoretical guidance for the application of treatment methods to increase TTL content.