Hydroponic cultivation of medicinal plants

Medicinal plants are specifically used for their contents of bioactive compounds, which are products of plant secondary metabolism with proven beneficial effects on human health. These substances are known to play a key role in the mechanisms of plant adaptation to the environment; they generally exhibit antioxidant properties and often act as defense molecules that are synthesized by plants in response to stress conditions. In the last decades, the interest by pharmaceutical companies towards the production of bioactive compounds from medicinal plants has considerably increased, especially in developed countries, in consideration of the consumers’ sensibility towards naturally sourced remedies. As a consequence, the traditional harvesting from the wild has become inadequate to sustain the market demand, and medicinal plants are increasingly cultivated on a commercial scale. On the other hand, the market requirement for standardized plant material cannot be fully satisfied by field crops, which are highly susceptible to year-to-year variability. Greenhouse hydroponics can contribute to overcome the drawbacks of conventional field cultivation, as it ensures a fast plant growth and allows both to control the growing environment and to change the composition of the nutrient solution that is fed to the plants. The application of a stress condition through a proper manipulation of the nutrient solution can stimulate secondary metabolism and promote the synthesis and accumulation of bioactive substances in plant tissues. This chapter presents some fundamental issues concerning the hydroponic production of raw plant material for the extraction of bioactive compounds. Literature data are reported on recent research concerning the hydroponic growing of medicinal plants, both under optimal conditions or under stress conditions to stimulate the production of secondary metabolites. Finally, basil is presented as a case study for the application of the hydroponic technique to the production of plant material for the extraction of rosmarinic acid, a bioactive secondary metabolite of well-known antioxidant activity. The present chapter points out the opportunities offered by the hydroponic growing of medicinal plants for the agro-industrial production of bioactive compounds. On the other hand, it also underlines the lack of information concerning the specific growing needs of the individual medicinal species. Despite the fact that at present a lot of molecules of pharmaceutical interest can be obtained from hydroponically-grown medicinal plants, suitable growing protocols are still required.