Influencing the Contents of Secondary Metabolites in Spice and Medicinal Plants by Deliberately Applying Drought Stress during Their Cultivation

Abstract

Medicinal plants grown under semi-arid conditions generally reveal significantly higher concentrations of relevant natural products than identical plants of the same species, which are cultivated in moderate climates. So far, there is very limited information on this well-known phenomenon. In the present study, corresponding data are compiled and relevant aspects are discussed. It turns out that metabolic reactions triggered by drought stress are responsible for the higher natural product accumulation in plants grown in semi-arid regions. The related plant physiological and biochemical background can be summarized as follows: In plants suffering drought stress, the water shortage caused by limited water supply triggers stomata closure. As a result, the uptake of CO2 is markedly decreased and the consumption of reduction equivalents (NADPH+H + ) consumed in the course of CO2-fixation via Calvin cycle declines considerably, generating a massive oversupply of NADPH+H + . Consequently, all metabolic processes are pushed towards the synthesis of highly reduced compounds, such as isoprenoids, phenols or alkaloids. Based on these considerations, impulses for novel practical approaches for enhancing the product quality by deliberately applying drought stress during the cultivation of medicinal plants are outlined. However, as drought stress concomitantly also leads to massive reductions in biomass production, special emphasis must be put on the interference of these stress related effects.