## 3 Discussion  
JA is widely present in the plant kingdom and belongs to the family of oxygenated fatty acid derivatives. It is synthesized via the oxidative metabolism of polyunsaturated fatty acids [35]. LA is oxygenated to 13(5)-hydroxy linolenic acid (13-HPOT) by the action of LOX. Under the actions of AOS and AOC, 13-HPOT then can be converted to 12-oxophyllotonic acid that can then be transformed to JA through reduction and three steps of \(\beta\)-oxidation. Among the enzymes in the JA synthesis pathway, LOXs are the most intensively studied enzymes. Plant LOXs are divided into two types including 9-LOXs and 13-LOXs. In the model plant _N. attenuata_, three different LOX isoforms are known. NaLOX3 is confirmed to be involved in the JA pathway and NaLOX2 has been shown to the pathway for green leaf volatiles [36; 37]. In response to herbivore attack, upregulation of _LOX3_ in _N. attenuata_ leaf is more sensitive than other genes involved in the JA pathway [5]. There are many reports concerning the effect of herbivore attack on genes in the JA synthesis pathway in plant vegetative parts, while little corresponding information is available for plant floral parts. Tea plants have no successful genetic transformation system, making it difficult to obtain in vivo evidence of metabolic pathways in tea plants. Our current knowledge concerning phytohormone and metabolite biosynthesis in tea plants is mostly based on reported findings for other plant species. Although some of these pathways are shared among plant species, there may also be variation among species because of the complexity of  
Figure 6: Effect of JA treatment on ethylene expression level and emission in tea flowers. CK, tea flowers without JA treatment. (**A**) Expression levels of ethylene synthesis genes and transcription factor in tea flowers and leaves, respectively which were treated by JA. Tea flowers and leaves were _C. sinensis_ cv. Jinxuan. (**B**) The content of flowers ethylene were collected and analysis was conducted by GC. Tea flowers were _C. sinensis_ cv. Yinghong NO. 9.  
the biosynthetic networks. Therefore, direct investigations of JA synthesis in tea plants are required. In the present study, CsAOS2 was confirmed to be involved in the biosynthesis of JA in tea flowers (Figure 3). The AOSs have been isolated and functionally characterized in several species of plants such as _Lycopersicon esculentum_, _Hordeum vulgar_, and _Solanum tuberosum_. These AOSs were reported to be located in the chloroplasts [26; 27; 28; 38]. These results suggest that CsAOS2, rather than CsAOS1, may be involved in JA biosynthesis in tea flowers. In future work, it would be of interest to investigate why CsAOS2 was upregulated in tea flowers exposed to _T. hawailiensis_ treatment while other genes were not significantly affected. There are a number of studies on the involvement of phytohormones in interactions between insects and flowers or leaves. Although some cases may be different in different plants, it is relatively universal that in most plants JA is typically reported to be involved in interactions between insects and plant vegetative parts while ethylene is mostly reported to be involved in interactions between insects and plant floral parts. Salicylic acid is mainly reported to be involved in interactions between microorganisms and plants, but it is also related to the interaction between insects and plant vegetative parts in some cases. More evidence suggests that, rather than individual phytohormones, interactions between insects and plants involve several phytohormones working together. Moreover, the phytohormone pathways may have antagonistic/synergistic cross-talk. For example, in maize, fungal infection reduced the emission of volatiles induced by lepidopteran herbivory alone by about 50%, possibly suggesting a diversion of plant resources from antiherbivore to presumptive antipathogen defenses.