## 4 Discussion
### Chemical Composition and Yields of Essential Oils from P. rivinoides
Conversely, if defenses are nonspecific, the same mechanism can increase the plant's ability to resist different aggressors, leading to synergistic or positive associations. In this sense, extrinsic factors of the plant may cause a lower energetic investment in the production of more complex and specific defense structures and, instead, direct its energy reserves towards the synthesis of less complex compounds that require less energy expenditure [70], a hypothesis to be confirmed. However, it is important to emphasize that this research addresses only a specific moment of the eco-physiology of _P. rivinoides_. Previous studies on this plant report low seasonal variation in the composition of EO, indicating that the predominant biosynthesis of the monoterenes \(\alpha\)- and \(\beta\)-pinene occurs continuously throughout the year [19; 71]. This absence of significant seasonal phenotypic variation is called seasonal monophenism [3]. Therefore, it is more likely that this continuous biosynthesis mechanism of pinene isomers at high content is considered an ideal defense mechanism, rather than an induced defense mechanism [20; 69; 72]. The theory of ideal defense suggests that defense compounds are produced or expressed in tissues with a higher likelihood or risk of being attacked [69; 71; 73]. Therefore, it is plausible that leaves and branches, being the structures responsible for photosynthesis and thus nutritional sources, accumulate a higher content of monoterenes with allebotathic function in their tissues as an ideal defense mechanism against herbivory [69; 71; 74]. While monoterenes were predominant in leaves and branches, in stems and roots the major component was the arylpropanoloid apiol. Based on the theory of optimal defense and considering the capacity of the same genotype to express different phenotypes, influenced by the environment, it can be concluded that different defense and tolerance strategies in different organs of the same plant are independent of each other and occur in an optimized manner [3; 75]. Thus, the presence of arylpropanoids in roots, stems, and young plants can be considered ideal defense mechanisms, as the synthesis of arylpropanoids promotes tissue production and, consequently, contributes to protection against pathogens [69; 71]. It is important to note that stems and roots have constitutive defenses that ensure greater expression of lignification in the cell walls of these tissues, making them more resistant to mechanical damage. In addition, resource allocation to produce defensive compounds depends on the intensity of herbivore attacks, and different defense and tolerance strategies are independent of each other [3; 76; 77]. Therefore, it is suggested that the presence of a high content of arylpropanoids and low content of \(\alpha\)-pinene in roots may also result from crosstalk with other organs, as roots are highly lignified underground organs [56; 74; 78]. Factors crosstalk integrate different physiological responses and optimizes the plant's fitness based on the resources available in the organ in question. Factors (genes, active enzymes, and hormones) of the organ in question dominate biosynthetic conductance. In other words, the accumulation of secondary metabolites in a specific organ comes from the production processes of the macromolecule related to the essential precursor [73; 75; 79]. For example, the roots of the studied plant accumulate a high content of arylpropanoids, compounds derived from the shikimate pathway, the same biosynthetic pathway for the formation of lignins (structural macromolecules). The roots and stems of _P. rivinoides_ are highly lignified, which indicates that the shikimate pathway is more highly expressed in these organs. Therefore, there will be a greater accumulation of arylpropanoids, biosynthetic precursors of lignans and lignins, in these organs. Thus, considering that the metabolic pathway with the highest activity in this organ is the shikimate pathway, the biosynthesis of arylpropanoids may be energetically more economical for the roots.