## 2 Results and Discussion
### OC Kappa Induced an Increase in Total Essential Oils and a Reprogramming of Terpenoid Metabolism
Thus, the increase in NADPH, ASC and GSH levels and in TRR/TRX activities induced by OC kappa determine, at least in part, the increase in total essential oils in _Eucalyptus_ trees. In addition, the inhibitors CHS-828, auranofine, lycorine and BSO completely inhibited the increase in the monoterenes silvestrene (Figure 3A), \(\beta\)-pinene (Figure 3B) and limonene oxide (Figure 3C) and that of the sequiterpene aromadrendene, \(\alpha\)-gurjunene (Figure 3A), viridflorene, myrcene (Figure 3B) and \(\gamma\)-cadinene (Figure 3C). In contrast, the increase in the monoterene \(\gamma\)-terpinene (Figure 3C) and the sequiterpene \(\alpha\)-guaiene (Figure 3C) was only partially inhibited by auranofine, lycorine and BSO and the increase in \(\gamma\)-gurjunene (Figure 3B) was partially inhibited by auranofine and BSO. Moreover, CHS-828, auranofine, lycorine and BSO completely inhibited the increase of _de novo_ synthesized terpenoids (data not shown). Thus, the increase in the synthesis of NADPH, ASC and  
Figure 2: Level of total essential oils in leaves of _Eucalyptus_ trees treated with water (control), with OC kappa at 1 mg\(\cdot\)mL\({}^{-1}\), or with CHS-828 and OC kappa (CHS+K), auranofine and OC kappa (Aur+K), lycorine and OC kappa (Lyc+K) and buthionine sulfoximine and OC kappa (BSO+K) and cultivated for 4 months. The level of essential oils is expressed in milligrams per gram of fresh tissue (FT). Bars represent mean values of three independent experiments and letters significant differences (\(p<0.05\)). GSH and TRR/TRX activities determine, at least in part, the increase in terpenoid synthesis and the reprogramming of terpenoid metabolism. Figure 3: Level of terpenoids (**A**–**C**) that increased in leaves of _Eucalyptus_ trees treated in control condition (control), treated with OC kappa at 1 mg\(\cdot\)mL\({}^{-1}\) (Kappa) or tretade with CHS-828 and OC kappa (CHS+K), auranofine and OC kappa (Aur+K), lycorine and OC kappa (Lyc+K) and buthionine sulfoximine and OC kappa (BSO+K) and cultivated for 4 months. Bars represent mean values of three independent experiments and letters significant differences (\(p<0.05\)). Regarding NADPHH and terpenoid synthesis, it has been shown that the enzyme of the mevalonate pathway 3-hydro-3 methylglutarate-CoA (HMG-coA) reductase, which is the limiting step of the pathway, require NADPH to synthesize mevalonate. In addition, the enzyme of the non-mevalonate pathway 1-deoxy-D-xylulose 5-P (DXP) reducto-isomerase requires NADPH to synthesize 2-methyl-3-erythritol 4-phosphate (MEP) [2,3]. Thus, it is not surprising that a decrease in NADPH synthesis inhibits terpenoid synthesis. Regarding TRR/TRX activities and terpenoid synthesis, it has been shown that chloroplasts TRXs \(f\) and \(m\) bind to DXP reducto-isomerase and GcpE enzyme belonging to the non-mevalonate pathway [26]. Considering that there is a cross-talk among NADPH, ASC and GSH that command the increase in TRR/TRX activities [20] and that TRX may activate at least the non-mevalonate pathway, it is possible to conclude that the increase in ASC and GSH may also regulate the increase in terpenoid synthesis. In addition, it is interesting to mention that _Eucalyptus_ trees treated with OC kappa cultivated in the field for three years showed an increase in polyphenic compounds with potential antipathogenic activities [19]. Thus, OC kappa activates the synthesis of volatile terpenoids and polyphenic compounds with antipathogenic activities which may enhance defense against insects and microbes in _Eucalyptus_ trees.