Drought Stress Effects on Medicinal and Aromatic Plants and the Possible Stress Amelioration by Mineral Nutrition

Limited water supply is one of the major abiotic factors that adversely affects agricultural crop production worldwide. Drought stress disturbs the balance between the production of reactive oxygen species (ROS) and the antioxidant defense, causing the accumulation of ROS that induce oxidative stress to proteins, membrane lipids and other cellular components. Drought stress hampers photosynthesis harshly owing to interference with stomatal functioning and causing serious damage to photosynthetic apparatus through ROS production. Hence, water-stressed plants exhibit disturbance in metabolism, particularly that of carbon, nitrogen and oxygen. As a result of water stress, growth parameters associated with root and above-ground parts, e.g. leaf area, height, and fresh and dry matter of plants, are severely reduced, leading to drastic reductions in growth, yield and quality of plants. Mineral elements have numerous functions in plants including charge balance, electron carriers, structural components, and enzyme activation. Besides, these elements behave as osmotica for maintenance of turgor and growth under drought stress. However, their uptake is reduced to a great extent under water deficit. Hence, their additional supplementation under water deficit results in improvement in their uptake and mitigation of deleterious effects of drought stress. A wide range of studies on the effect of drought stress on growth, yield and quality of field crops have been conducted; however, such studies related to medicinal and aromatic plants (MAPs) are few. In this review, in addition to describing the adverse effects of water stress on the growth, yield and quality attributes of MAPs, the ameliorative role of some of the macronutrients (nitrogen, phosphorus, potassium, and calcium) is discussed. _____________________________________________________________________________________________________________