L-DOPA and Dopamine in Plant Metabolism

Nonprotein amino acids are widely distributed in the plants. They constitute a numerous group of secondary metabolites and represent a relevant reservoir of nitrogen and carbon. Among them, L-3,4-dihydroxyphenylalanine (L-DOPA) and 3,4-dihydroxyphenethylamine (dopamine) possess relevant physiological and biochemical effects on plants. L-DOPA, a strong allelochemical released by Mucuna plants into soils, is a precursor of many alkaloids, melanin, and catecholamines such as norepinephrine (noradrenaline) and epinephrine (adrenaline). In plants, dopamine is produced via hydroxylation of tyramine or decarboxylation of L-DOPA. Because L-DOPA and dopamine reveal striking roles in plant communication and signaling, we revise in this chapter the state of current knowledge on their biosynthesis, oxidation, functions, and prooxidant and antioxidant activities.