# Functions of Representative Terpenoids and Their Biosynthesis Mechanisms in Medicinal Plants
## 4 Effects of Environmental Factors on Terpenoid Accumulation  
Synthesized and accumulated terpenoids are tightly regulated by changing abiotic environments (Figure 2) [46; 47]. Light plays a critical role in terpenoid accumulation, which cannabinoid synthesis is a wonderful example. To achieve a consistent production of cannabis products, it is increasingly being grown indoors using Light Emitting Diode (LED) light, which is more energy efficient than traditional high-pressure sodium (HPS) light sources. Higher cannabinoid concentrations are measured under LED lighting compared to HPS [48]. Similarly, cannabinoid acid (CBGA) was accumulated up to 400% more during LED treatments compared to HPS [49]. Moreover, combining LED light and metal halide lamps increased bud yield and cannabinoid concentrations [50]. Blue light LED can also lead to increased cannabinoid concentration in C. _sativa_[51; 52; 53]. The dynamic spectrum LED treatment leads to increase in yield and significant improvement in cannabinoid content compared to fixed full-spectrum white light [54],When plants are exposed to a strong light intensity or ultraviolet-B (UV-B) radiation, they can initiate the terpenoid metabolite biosynthesis for antioxidant defense [55]. For instance, there is a positive association between UV-B radiation and cannabinoid content in _C. sativa_[56]. After exposure to UV light for 24 h and 48 h, the terpenoid content increased by 10.0% to 21.9% in _G. biloba_[57]. Artemisinin accumulation also correlates positively with light intensity, with the highest concentration observed at 3000 Lux when exposed to a standard fluorescent lamp [58]. Cold stress, such as chilling (0-15 \({}^{\circ}\)C) and freezing (<0 \({}^{\circ}\)C), adversely affects plant development, but facilitates terpenoid accumulation [59]. The artemisinin content increased  
Figure 2: Terpenoid-mediated plant-environment interactions. Medicinal plants produce terpenoids to inhibit insect feeding and pathogen attack, whereas UV-B radiation, drought, salt, and temperature stress can induce terpenoids accumulation in medicinal plants. by 27.16% upon exposure to cold stress and overnight frost in _A. annua_[60; 61]. In addition, cold stress (4 \({}^{\circ}\)C) also significantly increased the terpenoid content in _G. biloba_, reaching a maximum at 8 d and increasing by 14.5% compared to the control [62]. Salt stress can increase the content of artemisinin by 14.68%, but prolonged salt stress decreases artemisinin accumulation [63]. In _C. sativa_, an increase in NaCl concentration was also found to result in a subsequent decrease in cannabinoid content [64; 65]. Drought can enhance terpenoid accumulation in medicinal plants (e.g., sesquiterpene content of _Salvia dolomitica_) [66]. The emission rates of terpenoid compounds are higher in cork oak and gum rock with increasing summer drought [67]. Similarly, there was a significant increase in the amount of (E)-\(\beta\)-caryophyllene in _O. vulgarte_ subsp. virens due to the drought [68]. Controlled drought stress can boost cannabinoid content in _C. sativa_[69]. Further research has shown that under drought stress, tanshinone enhances the photosynthetic capacity and prevents oxidative damage, thus improving drought stress resistance in _S. miltiorhiza_[70]. Although the existing studies have discovered various external factors that can regulate terpenoid synthesis in medicinal plants, research on the regulatory pathways affected by these environmental factors is still very limited. Due to the importance of the environment in promoting the accumulation of terpenoids, further research should be conducted in the future to investigate various environmental factors and their combinations that regulate terpenoids accumulation in medicinal plants. By considering the characteristics of different medicinal plants, the most advantageous combination of environmental factors for terpenoid accumulation should be optimized and selected.