Influencing the Product Quality by Applying Drought Stress During the Cultivation of Medicinal Plants

Abstract

When medicinal plants are grown under semi-arid conditions, they generally reveal significantly higher concentrations of relevant natural products than identical plants of the same species, which however are cultivated in moderate climates. Up to now, only limited information on this well-known phenomenon is available. In this treatise, corresponding data are compiled and relevant aspects are discussed. It becomes obvious that drought stress-related metabolic changes are responsible for the higher natural product accumulation in plants grown in semi-arid regions. The corresponding plant physiological and biochemical background is outlined as follows: Due to limited water supply and much higher light intensities, the plants suffer drought stress. The related water shortage leads to stomata closure and as a result the uptake of CO2 is markedly decreased. Accordingly, the consumption of reduction equivalents (NADPH+H+) for the CO2-fixation via Calvin cycle declines considerably, generating a massive oversupply of NADPH+H+. As a consequence, metabolic processes are pushed towards the synthesis of highly reduced compounds like isoprenoids, phenols or alkaloids. Based on these coherences, impulses for novel practical approaches for enhancing the product quality by deliberately applying drought stress during the cultivation of medicinal plants are given. However, as drought stress concomitantly leads to massive reductions in biomass production, special emphasis is put on the interference of these stress-related effects.