The production of secondary metabolites from medicinal plants, also called Plant-Derived Medicinal Compounds (PDMC), is gaining ground in the last decade. Concomitant to the increase in the knowledge about pharmacological properties of these compounds, horticultural plants are becoming the most important, sustainable and low-cost biomass source to obtain high-complex PDMCs to be used as medicaments. Biotechnological tools, including plant cell and tissue culture and plant genetic transformation, are increasingly being employed to produce high quality and rare PDMC under in vitro conditions. The proper use of these technologies requires studies in organogenesis to allow for better control of in vitro plant development and, thus, to the production of specific tissues and activation of biochemical routes that result in the biosynthesis of the target PDMCs. Either biotic or abiotic factors, called elicitors, are responsible for triggering the PDMC synthesis. In vitro techniques, when compared to the conventional cultivation of medicinal plants in greenhouse or in the field, have the advantages of (1) producing PDMCs in sterile and controlled environmental conditions, allowing better control of the developmental processes, such as organogenesis, and (2) producing tissues with high PDMC contents, due to the efficient use of different biotic and abiotic elicitors. Nevertheless, the process has many challenges, e.g., the establishment of step-by-step protocols for in vitro biomass and PDMC production, both involving and being affected by many factors. Other limitations are the high costs in opposition to the relatively cheaper alternative of growing medicinal plants conventionally. This paper aims to quickly review the general origin of plant secondary metabolites, the leading techniques and recent advances for PDMC in vitro production, and the challenges around the use of this promising technology.

The efficient production of plant-derived medicinal compounds (PDMCs) from in vitro plants requires improvements in knowledge about control of plant or organ development and factors affecting the biosynthesis pathway of specific PDMCs under in vitro conditions, leading to a realistic large-scale tool for in vitro secondary metabolite production. Thus, this study aimed to develop an in vitro technique, through the induction and proliferation of calli, for production of plant fresh weight, and to compare the PDMC profile obtained from the plants versus in vitro calli of Phyllanthus amarus. It was successfully possible to obtain and proliferate two types of calli, one with a beige color and a friable appearance, obtained in the dark using Murashige and Skoog (MS) medium plus 2,4-dichlorophenoxyacetic acid (2,4-D), and a second type with a green color, rigid consistency, and nonfriable appearance obtained under light conditions and MS medium plus 6-benzyladenine (6-BA). In vitro micropropagated plants that gave rise to calli were also acclimatized in a greenhouse and cultivated until obtaining the mass for PDMC analysis and used as a control. While the micropropagated-derived plants concentrated the lignans niranthin, nirtetralin, and phyllanthin, the Phyllanthus amarus calli proliferated in vitro concentrated a completely different biochemical profile and synthesis of compounds, such as betulone, squalene, stigmasterol, and β-sitosterol, in addition to others not identified by GC-MS database. These results demonstrate the possibility of applying the calli in vitro from Phyllanthus amarus for production of important PDMCs unlike those obtained in cultures of differentiated tissues from field plants.