# Effects of Temperature on Growth and Isoprene Metabolism Pathway in _Eucomnia ulmoides_ [PERSON]
## 4 Discussion  
Prolonged cold and heat stress during early growth can significantly hinder plant growth, leading to reduced plant heights and growth rates. Moreover, decreased photosynthesis and chlorophyll content have been documented in response to extreme temperatures. Factors such as leaf and stem scorching, as well as leaf abscission, further exacerbate the decline in yield [31; 32; 33]. Notably, chlorophyllase plays a pivotal role in catalyzing the hydrolysis of chlorophyll, forming chlorophyll lactones. A negative correlation exists between chlorophyll content and chlorophyllase activity [34]. Moreover, chlorophyllase is responsive to environmental stress, and environmental factors, such as strong light, pathogen infection, and leaf cell destruction, can accelerate chlorophyll degradation [35; 36]. Our study revealed that growth parameters (e.g., plant height, leaf length, leaf width, specific leaf weight, and chlorophyll content) of _E. ulmoides_ seedlings were affected by LT and HT treatments. Additionally, the expression of the _CLH_, responsible for chlorophyll degrada  
Figure 8: The differentially expressed genes between HT and control verified using RT-qPCR: (**A**) _EuFPS1_; (**B**) _EuPPI_; (**C**) _EuDXS3_; (**D**) _EuACAT3_; (**E**) _EuHMSG2_; (**F**) _EuGGPS2_; (**G**) _EuSRPP6_. tion, was upregulated, suggesting that HT treatment accelerates chlorophyll decomposition and leads to reduced chlorophyll content. This is consistent with previous research. Earlier studies have confirmed that _HMGR_ is involved in rubber biosynthesis and associated with the biosynthesis of other terpen [23; 37]. A modest increase in geranyl/symorphosphate synthase (GPPS) activity boosts monoterpene production in transgenic tobacco [38]. Additionally, high temperature has been found to favor the expression of the Ginkgo _GGPP_ gene [39]. Farnesyl pyrophosphate synthase (FPS) synthesizes FPP, which is conducive to the biosynthesis of rubber [40]. A study has demonstrated that TPS affects the concentration of IPP and DMAPP, as well as the flow direction, consequently impacting the rubber content [41], and its expression was mostly increased under osmotic stress and heat stress conditions [42]. Studies have indicated that cold and heat stress can affect the content of rubber and other terpen [43; 44; 45], with rubber content decreasing and terpene content increasing under adversity. [PERSON] noticed that IPP is used for the synthesis of carotenoids and rubber in _Hewen brasiliensis_[46]. In this study, the rubber content of LT and HT groups was significantly lower than that in the control group. However, the total triterpene content of LT and HT groups was significantly higher than that of control group. Analysis of the gene expression profiles related to the isoprene pathway revealed increased expression levels of _HMGS2_, _HMGR_, _DXS_, and _IPPI_ under HT treatments. This enhanced expression facilitated the synthesis of IPP, a crucial precursor for the production of isoprene-like metabolites, ultimately laying the foundation for isoprene-like substance synthesis. However, while IPP precursor synthesis increased, _GPS2_ and _GPS3_ genes were downregulated at high temperatures, resulting in the reduced synthesis of GPP, the precursor for FPP synthesis. The majority of the synthesized GPP was directed toward monoterpene production. Furthermore, the expression of the _FPS1_ gene, responsible for FPP synthesis, was downregulated at high temperatures, leading to a decrease in FPP synthesis. Conversely, the expression of the _GGPS_ gene, catalyzing GGPP synthesis using FPP, increased at high temperatures. Additionally, the expressions of most _TPS_ genes were found to be upregulated. As a result, the synthesized FPP was primarily utilized for GGPP synthesis as well as the production of sesquiterpenes and triterpenes.