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Acid rain (AR) is a serious global environmental issue causing physio-morphological changes in plants. Melatonin, as an indoleamine molecule, has been known to mediate many physiological processes in plants under different kinds of environmental stress. However, the role of melatonin in acid rain stress tolerance remains inexpressible. This study investigated the possible role of melatonin on different physiological responses involving reactive oxygen species (ROS) metabolism in tomato plants under simulated acid rain (SAR) stress. SAR stress caused the inhibition of growth, damaged the grana lamella of the chloroplast, photosynthesis, and increased accumulation of ROS and lipid peroxidation in tomato plants. To cope the detrimental effect of SAR stress, plants under SAR condition had increased both enzymatic and nonenzymatic antioxidant substances compared with control plants. But such an increase in the antioxidant activities were incapable of inhibiting the destructive effect of SAR stress. Meanwhile, melatonin treatment increased SAR-stress tolerance by repairing the grana lamella of the chloroplast, improving photosynthesis and antioxidant activities compared with those in SAR-stressed plants. However, these possible effects of melatonin are dependent on concentration. Moreover, our study suggests that 100-μM melatonin treatment improved the SAR-stress tolerance by increasing photosynthesis and ROS scavenging antioxidant activities in tomato plants.

Essential oils are the volatile compounds having the oily fragrance. Essential oils are obtained from the different plant parts, and they are extracted from the different techniques and the most preferable method of extraction is the hydrodistillation which is cheap and easy to use. Plant parts including the flowers, leaves, stem, bark and roots are used for the isolation of essential oils. Essential oils are used in almost every field of life and because of these characteristics, the market of essential oils is growing rapidly. Essential oils are used in the aromatherapy and act as antioxidant, antimicrobial, antifungal, pain relievers, anxiety, depression. In the field of cosmetics and industries, the essential oils are used rapidly and mostly used in the perfume industries which are growing increasingly. Essential oils are used in the food preservations and many food items. Essential oils are used as the folk herbal medicines and their fragrance is used for the improvement of the mood and as the depression release.

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