## 4 Discussion
### Chemical Composition and Yields of Essential Oils from P. rivinoides
It is important to recognize that EO production in plants is a complex and multifaceted process, involving interactions between a variety of biotic and abiotic factors, as mentioned. Therefore, in some specific cases, it may be challenging to detect clear patterns in field studies due to the complexity of the system. Regarding the chemical composition, the major constituents found in the samples were the monoterenes \(\alpha\)-pinene, \(\beta\)-pinene, and the arylpropanol apiole (Figure 1). The Venn diagram showed that the monoterrene \(\alpha\)-pinene is the only compound present in all organs of \(P\). _rivinoides_, and in all phases of the plant's ontogenetic development (Figure 2). It is important to note that \(\alpha\)-pinene is a common monoterrene found in the EO of conferous trees, such as the genera _Pinus_ and _Pica_, as well as in the genus _Eucalyptus_[51; 52; 53]. \(\alpha\)-pinene has two structural isomers, \(\alpha\)-pinene and \(\beta\)-pinene, which are responsible for the characteristic aromas of pine and turpentine oil, respectively. Additionally, two pairs of enantiomeric isomers of these monoterrenes naturally coexist in nature: \((-)\)-\(\alpha\)-pinene and \((+)\)-\(\alpha\)-pinene, and \((-)\)-\(\beta\)-pinene and \((+)\)-\(\beta\)-pinene [54; 55]. However, in our analysis, it is not possible the separation of the enantiomers \((-)\) and \((+)\). PCA showed greater similarity among the chemical constituents of leaves and branches compared to roots and stems, although the Euclidean distance between clusters was relatively low. These differentiation trends among Piperaceae organs have been demonstrated in the literature [6; 56]. The biosynthesis of \(\alpha\)-pinene and \(\beta\)-pinene occurs via the mechanate pathway from geranyl pyrophosphate (GPP) through the cyclization of linalyl pyrophosphate, followed by proton loss. Consequently, their biosynthesis is considered less complex, occurring at the beginning of the terpene biosynthetic pathway [57]. Although studies on the chemical/ecological function and functionality of pineinee isomers are incipient, they encompass a wide range of functions. Actions include protection against herbivores [58]; repellent action [51]; antibacterial activity [59; 60]; attraction of pollinators with insect-plant interaction [61], where they perform signaling functions within a population/community or even in adjacent plants; an inhibitory effect on the spore formation of _Metathizium_ fungi, even at concentrations below 5% [62]; regulation of leaf temperature [62; 63; 64]; participation in allelochemical communication [65]; inhibition of root growth [65; 66]; induction of oxidative stress [67; 68]; alteration of chlorophyll content; and decrease in seedling biomass [68]. Overall, the significant presence of pinees, especially \(\alpha\)-pinene, becomes more prominent in leaves and branches compared to stems and roots. It has been demonstrated that pinees play a role in conifer resistance against beetles and associated fungi [55]. Therefore, it is plausible that _P. rivinoides_ accumulates higher content of these pinees in its leaves as a physiological response to external stimuli. The monoterpene cyclase enzyme has been reported to increase its activity (U) in response to elicitors, which are often found in insect saliva. This suggests that the production of \(\alpha\)-pinene and \(\beta\)-pinene may function as an inducible chemical defense, particularly in leaves, though roots also show a response [20; 69]. Another important point to consider is that _P. rivinoides_ is probably consumed by generalist herbivores, as different patterns of herbivory have been observed in the field on the leaves (unpublished data), suggesting that this organ is attacked by different insects. If a plant's defenses are specifically adapted to combat a particular herbivore and require a high investment of resources, there may be trade-offs between different strategies.