## 1 Introduction  
Levo 3,4-dihydroxyphenylalanine (L-DOPA) therapy is necessary for [PERSON]'s disease for its powerful antiparkinsonian effect [1]. L-DOPA is a nonprotein amino acid with biological activity, found in animals and in some plants [2]. It is the precursor of catecholamine type neurotransmitters (dopamine, norepinephrine, and epinephrine), being involved in melanin synthesis as well [3]. L-DOPA has drawn much attention in the field of plants for its acknowledged defensive role against insects [4]. In addition, it is considered an allelochemical, i.e., a compound released into the environment affecting the growth and development of neighboring plants [1; 5; 6]. L-DOPA has raised particular interest in legumes, particularly in the Fabaceae family, as reports describe a relatively high content in such plants [7; 8]. Additionally, for [PERSON]'s patients, fava bean consumption would be even better than the drug in terms of motor performance and side effects [1]. Moreover, carbidopa (a peripheral inhibitor of the enzyme DOPA decarboxylase) has been found in fava bean as well [9]. Thus, different tissues of fava bean have been analyzed for L-DOPA, and as much as 6.0-6.75% dry weight (DW) (60-67.5 mg g\({}^{-1}\) DW) has been found in young pods of cultivars Diana and Alameda, respectively [10], and contents in whole seedlings in the order of 0.2% DW (2 mg g\({}^{-1}\) DW) [11]. L-DOPA would be produced via the oxidation of the phenolic amino acid L-4-hydroxyphenylalanine (tyrosine) by the enzyme tyrosinase (tyrosine oxidase: TYROX) [12]. In turn, tyrosine comes in plants from the shikimic acid pathway and TYROX would be involved in L-DOPA synthesis in non-Cariophyllalles plants [13]. TYROX is involved in other polyphenics and melanin synthesis, as well [6]. L-DOPA is a melanin biosynthetic precursor (present in plant and animal tissues). In general, TYROX are multicopper monophenol monooxygenenses (EC 1.14.18.1), which use oxygen as cosubstrate to catalyze the o-hydroxylation of phenols (i.e., tyrosine to L-DOPA step); and the subsequent oxidation of the formed o-diphenylols to the corresponding o-quinones as well. Thus, using the aromatic amino acid L-tyrosine as substrate, the ultimate tyrosinase-catalyzed reaction product is dopaquinone [13]. This o-quinone can undergo chemically spontaneous and also enzymatic reactions, which in turn can further convert it into melanin. Therefore, TYROX is considered a key enzyme for melanin synthesis [14] and has also been associated with stress responses to the environment, as melanin plays a survival function [15]. L-DOPA is also a precursor of phenylpropanoids in plants; the phenylpropanoid pathway is an important metabolic route, as it synthesizes phenolic compounds, including lignin [16]. Indeed, in plants, TYROX plays an important role in modifying and hardening the protective exterior layer of, for instance, seed envelopes, and as an agent against invasive organisms [16]. In plants, a common early response to environmental changes is the antioxidant enzymatic pathway, with roles in signal transduction and pathogen defense, producing protective biomolecules such as melanin and lignin [17]. GPX (Guaicaol peroxidase, (EC 1.11.1.7)) is a heme-containing protein that oxidizes certain phenolic substrates at the expense of H\({}_{2}\)O\({}_{2}\)[18]. GPX is considered a marker phenolic compounds metabolism and antioxidant response. Indeed, GPX has a role in the biosynthesis of lignin, the defense against biotic stresses, decomposition of indole-3-acetic acid (IAA), among others [19; 20], and is widely accepted as a'stress enzyme'. Amongst the various antioxidant enzymes, GPX can be considered one of the key ones, since both of its extra and intracellular forms participate in the breakdown of H\({}_{2}\)O\({}_{2}\)[15; 20]. In an effort to stimulate L-DOPA production in fava bean, [PERSON] et al. [21] studied L-DOPA content in seedlings, primed with oregano extract, lactoferrin, and a fish protein hydrolysate (dark germination).