Drought poses a significant challenge, restricting the productivity of medicinal and aromatic plants. The strain induced by drought can impede vital processes like respiration and photosynthesis, affecting various aspects of plants’ growth and metabolism. In response to this adversity, medicinal plants employ mechanisms such as morphological and structural adjustments, modulation of drought-resistant genes, and augmented synthesis of secondary metabolites and osmotic regulatory substances to alleviate the stress. Extreme water scarcity can lead to leaf wilting and may ultimately result in plant death. The cultivation and management of medicinal plants under stress conditions often differ from those of other crops. This is because the main goal with medicinal plants is not only to increase the yield of the above-ground parts but also to enhance the production of active ingredients such as essential oils. To elucidate these mechanisms of drought resistance in medicinal and aromatic plants, the current review provides a summary of recent literature encompassing studies on the morphology, physiology, and biochemistry of medicinal and aromatic plants under drought conditions.

Faba bean (Vicia faba L.) is a cool season grain legume crop with the potential to be grown as multi-purpose crop in areas with short growing season. Faba bean is grown in many regions in the world due to its high nutritional value, medicinal effect, and effective biological nitrogen fixation. Diverse ecosystem benefits are expected from integrating faba bean in cropping systems. This paper specifically reviews the published work covering agronomic practices, nutritional values, medicinal benefits, and faba bean's capacity for nitrogen fixation.

Faba bean (Vicia faba L.) has been identified as a rich source of L-DOPA, which is used in treating Parkinson's disease. Biosynthesis and accumulation of active substances such as L-DOPA in plant tissues may interact with growing conditions and processing methods. Accumulation trends of L-DOPA in various faba bean organs and the effect of drought stress and N fertilization on L-DOPA content were studied in a field and two greenhouse experiments. The influence of various processing methods on L-DOPA content of faba bean tissues was evaluated. The highest L-DOPA content was detected in fresh leaves (22.4 mg g⁻¹) followed by flowers, young pods, mature seeds, and roots. Regardless of processing method, L-DOPA concentration in faba bean tissues was significantly reduced when tissues were boiled or dried. Among various methods of processing, freezing had the lowest detrimental effect, reducing L-DOPA concentrations by 24.1% and 21.1% in leaves and seeds, respectively. Drought stress elevated L-DOPA concentration, and maximum L-DOPA (23.3 mg g⁻¹ of biomass) was extracted from plants grown under severe drought stress. However, L-DOPA yield (L-DOPA concentration × biomass) was compromised, owing to the adverse influence of drought stress on dry matter production. No significant difference in L-DOPA concentration was detected among various N application rates.

Thymus daenensis, a perennial herb, is often grown in areas that experience drought conditions during its growing period. Application of chitosan may compensate for the negative impact of drought stress on the yield of oil and secondary metabolites in Thymus. The interactive effects of foliar application of chitosan and drought stress on dry matter, essential oil yield, and selected physiological characteristics including photosynthetic pigments, osmotic adjustment, and lipid peroxidation of Thymus were investigated in a two-year study from 2014 to 2015. Treatments consisted of 0, 200, and 400 μL L⁻¹ chitosan applied to plants grown under field capacity, mild drought stress (50% field capacity), and severe drought stress (25% field capacity). Dry matter yield decreased substantially as drought stress intensified. However, essential oil content increased under stress conditions, with the highest essential oil yield obtained from plants under mild drought stress. Foliar application of chitosan compensated to some extent for dry matter and oil yield reduction of plants grown under drought stress. The highest essential oil yield (1.52 g plant⁻¹) was obtained by application of 400 μL L⁻¹ chitosan under the mild stress condition in 2015 when plants were mature. The compensatory effect of chitosan in reducing the negative impact of stress conditions on dry matter and oil yield was due mainly to stimulation of osmotic adjustment through proline accumulation and reduction of lipid peroxidase level, which increased the integrity of cell membranes of thyme leaves.