Univrsity of Tehran Press Iranian Journal of Field Crop Science 2008-4811 55 2 2024 06 21 Investigating the Physiological Response of Ammi majus (L.) Leaf Tissue to Melatonin under Heat Stress Investigating the Physiological Response of Ammi majus (L.) Leaf Tissue to Melatonin under Heat Stress 141 152 96628 10.22059/ijfcs.2024.364404.655025 FA Fatemeh Alizadeh Department of Agricultural Biotechnology, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran. Sajad Rashidi Monfared Department of Agricultural Biotechnology, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran. Amin Ebrahimi Department of Agricultural Biotechnology, Faculty of Agriculture, Shahrood University of Technology, Shahrood, Iran. Journal Article 2023 08 29 Traditional medicine has been successful in treating chronic diseases and their related problems. Considering the very high importance of medicinal plants and the growing need for the cultivation of these plants, especially <em>Ammi majus</em> plant due to its very effective medicinal compounds, it seems that the use of external stimuli in order to increase the quantity and quality of secondary metabolites can be effective as an auxiliary method in the cultivation of this plant. This plant is thermophilic and tolerates heat to some extent. In this research, different levels of melatonin (0, 30, 60 ppm) and time intervals of 24 and 48 hours were used. The results of this research showed that the use of different levels of melatonin, especially the concentration of 60 ppm, effectively prevented the destruction of the pigments of plants under heat stress, and even their amount increased approximately 2 times at 60 ppm compared to 0 concentration. At the same time, melatonin increased the activity of antioxidant enzymes and thus led to a decrease in the content of reactive oxygen species that were increased under heat stress. The amount of malondialdehyde has also decreased twice as a result of melatonin spraying, especially 60 ppm. The result was the reduction of free radicals, reduction of electrolyte leakage, malondialdehyde content, and finally, the increase of tolerance of plants under heat stress. Generally, it can be concluded that melatonin as a functional stimulant is capable of stimulating physiological changes in plants treated with heat with the aim of increasing their tolerance. Traditional medicine has been successful in treating chronic diseases and their related problems. Considering the very high importance of medicinal plants and the growing need for the cultivation of these plants, especially <em>Ammi majus</em> plant due to its very effective medicinal compounds, it seems that the use of external stimuli in order to increase the quantity and quality of secondary metabolites can be effective as an auxiliary method in the cultivation of this plant. This plant is thermophilic and tolerates heat to some extent. In this research, different levels of melatonin (0, 30, 60 ppm) and time intervals of 24 and 48 hours were used. The results of this research showed that the use of different levels of melatonin, especially the concentration of 60 ppm, effectively prevented the destruction of the pigments of plants under heat stress, and even their amount increased approximately 2 times at 60 ppm compared to 0 concentration. At the same time, melatonin increased the activity of antioxidant enzymes and thus led to a decrease in the content of reactive oxygen species that were increased under heat stress. The amount of malondialdehyde has also decreased twice as a result of melatonin spraying, especially 60 ppm. The result was the reduction of free radicals, reduction of electrolyte leakage, malondialdehyde content, and finally, the increase of tolerance of plants under heat stress. Generally, it can be concluded that melatonin as a functional stimulant is capable of stimulating physiological changes in plants treated with heat with the aim of increasing their tolerance. https://ijfcs.ut.ac.ir/article_96628_1d6d72862cd06db1db6a8c715a965597.pdf