Medicinal Plant Research 2024, Vol.14, No.4, 223-233 http://hortherbpublisher.com/index.php/mpr 229 triterpenoid metabolism, thereby enhancing GA production (Meng et al., 2022a). This indicates that the combined effects of various environmental stressors can lead to a more robust and diverse secondary metabolite profile in G. lucidum. 7 Case Studies 7.1 Temperature stress and triterpenoid production Temperature stress has been shown to significantly impact the biosynthesis of ganoderic acid (GA), a key triterpenoid in Ganoderma lucidum. High temperatures increase the levels of nitric oxide (NO) and calcium ions (Ca2+), which interact to regulate GA production. Specifically, heat stress (HS) elevates NO levels by 120%, which in turn modulates GA biosynthesis. The application of a NO scavenger increases GA content by 25%, while a NO donor decreases it by 30%, indicating that NO alleviates HS-induced GA accumulation. Furthermore, the cross-talk between NO and Ca2+ signals is crucial, with Ca2+ having a more direct and significant effect on GA production under HS conditions (Liu et al., 2018a). 7.2 The role of drought in altering polysaccharide biosynthesis Water stress, or drought conditions, significantly affects the biosynthesis of polysaccharides and ganoderic acid in Ganoderma lucidum. Under water stress, the intracellular reactive oxygen species (ROS) levels, GA content, and NADPH oxidase (NOX) activity increase. The expression of the G. lucidum aquaporin (GlAQP) gene, which facilitates water transfer, is induced, enhancing microbial growth. In GlAQP-silenced strains, water stress results in higher ROS levels and GA content compared to wild-type strains. Conversely, in GlAQP-overexpressing strains, ROS levels and GA content are lower. This indicates that the cross-talk between GlAQP and NOX modulates GA biosynthesis via ROS under water stress, with the regulation being positive at the early stage and negative at the late stage of fermentation (Zhu et al., 2022) (Figure 4). Figure 4 Effect of silencing NOX and adding DPI on ROS level and GA content of G. lucidumunder water stress (Adopted from Zhu et al., 2022) Image caption: (A) Change in ROS level detected by DCFH-DA staining in NOX-silenced strains and 10 μM DPI-treated WT under water stress. (B) Change in ROS fluorescence ratio in NOX-silenced strains and 10 μM DPI-treated WT under water stress. (C) The GA content in NOX-silenced strains and 10 μM DPI-treated WT under water stress. The values indicate the mean ± SD of three independent experiments. Different letters indicate significant differences between treatments (Duncan’s multiple range test, P < 0.05) (Adopted from Zhu et al., 2022)
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