Medicinal Plant Research 2024, Vol.14, No.4, 223-233 http://hortherbpublisher.com/index.php/mpr 225 Temperature Stress: Both high and low temperatures can affect the physiological processes of G. lucidum. Heat stress, for instance, has been shown to inhibit mycelium growth, reduce hyphal branching, and induce the accumulation of heat shock proteins (HSPs) and ganoderic acid (GA) (Zhang et al., 2016). Water Stress (Drought): Water scarcity is another critical stressor that affects G. lucidum. Water stress increases intracellular reactive oxygen species (ROS) levels, which in turn influences the biosynthesis of ganoderic acid and the activity of NADPH oxidase (NOX) (Zhu et al., 2022). Salinity Stress: Although not extensively covered in the provided data, salinity stress generally affects the osmotic balance and can lead to similar physiological responses as drought stress. Oxidative Stress: This type of stress is often a secondary effect of other environmental stressors like drought and temperature extremes. Increased ROS levels under oxidative stress can lead to cellular damage but also play a role in signaling pathways that regulate secondary metabolite production (Zhang et al., 2016; Zhu et al., 2022). 3.2 Physiological responses of Ganoderma lucidumto stress The physiological responses of G. lucidumto environmental stress are multifaceted and involve various cellular mechanisms: Heat Stress Response: Under heat stress, G. lucidum exhibits inhibited mycelium growth and reduced hyphal branching. There is also an induction of HSPs and an increase in cytosolic Ca2+ concentration, which is crucial for heat shock signal transduction (Zhang et al., 2016) (Figure 1). Water Stress Response: Water stress leads to an increase in ROS levels, which subsequently enhances the biosynthesis of ganoderic acid. The expression of the aquaporin gene (GlAQP) is induced to facilitate water transfer, aiding in microbial growth under water-limited conditions (Zhu et al., 2022). Oxidative Stress Response: Elevated ROS levels under oxidative stress can activate signaling pathways that modulate the production of secondary metabolites like ganoderic acid. The interaction between GlAQP and NOX plays a significant role in this process (Zhu et al., 2022). Figure 1 Schematic representation showing that HS regulates HSP expression, hyphal branching, and GA biosynthesis via cytosolic Ca2+ inGanoderma lucidum(Adopted from Zhang et al., 2016) Image caption: HS-induced cytosolic Ca2+ regulates GA biosynthesis, HSP accumulation, and hyphal branching. The black solid arrows indicate data supported by our own experiments, and the dotted arrows indicate data experimentally supported in other fungal systems (Adopted from Zhang et al., 2016) 3.3 Changes in metabolite production under stress conditions Environmental stressors can significantly alter the production of secondary metabolites in G. lucidum. Both heat and water stress have been shown to increase the production of ganoderic acid. Under heat stress, the
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