Document Type : Research Paper
Authors
1 PhD student in Horticultural Sciences and Engineering, Faculty of Agriculture, University of Tabriz, Tabriz, Iran.
2 Associate Professor, Department of Horticultural Sciences and Engineering, Ahar Faculty of Agriculture and Natural Resources, University of Tabriz, Tabriz, Iran.
Abstract
Objective: The increasing global population and the growing demand for medicinal plants in the pharmaceutical industry highlight the importance of active compounds derived from these plants across various sectors. This trend has led to a significant rise in the cultivation of medicinal plants, particularly Moldavian balm (Dracocephalum moldavica L.), which has gained popularity worldwide. However, as the cultivation of Moldavian balm expands, it is likely to encounter abiotic stresses, particularly water deficit stress, during its growing season. Drought stress can severely affect plant health by disrupting physiological and metabolic functions. In this context, melatonin has emerged as a crucial regulator of plant biological responses, modulating various physiological processes and enhancing resilience to stress conditions. Therefore, considering the limited water resources in the country and the positive effects of melatonin on plants, as well as the medicinal importance of Moldavian balm, this research was conducted with the aim of investigating the effect of melatonin on improving the physiological properties of the medicinal plant Moldavian balm in greenhouse cultivation.
Method: In this study, we investigated the effects of different concentrations of melatonin (such as control, 50, and 100 micromolar) on the physiological characteristics of Moldavian balm subjected to varying levels of drought stress (including 25%, 50%, 75%, and 100% of field capacity). The experimental design employed was a factorial arrangement in a completely randomized block design with three replications, allowing for robust statistical analysis of the results. This experiment was conducted in the greenhouse and laboratory of the Faculty of Agriculture and Natural Resources, Ahar, University of Tabriz.
Results: The application of 100 µM melatonin significantly enhanced the levels of photosynthetic pigments in Moldavian balm. This increase is crucial as chlorophyll and carotenoids are vital for photosynthesis, enabling plants to convert light energy into chemical energy efficiently. Enhanced photosynthetic activity directly correlates with improved growth and productivity, especially under stress conditions. The study revealed that melatonin treatment, particularly at the 100 µM concentration, led to a marked increase in secondary metabolites, including phenolic compounds and flavonoids. These compounds are known for their role in plant defense mechanisms, providing protection against environmental stressors, including drought. The highest recorded levels of phenol (51.952 mg gallic acid g-1 FW) and flavonoid (11.424 mg quercetin g-1 FW) were observed in the melatonin-treated plants, indicating enhanced protective capabilities. The activity of antioxidant enzymes, specifically phenylalanine ammonia-lyase, was significantly elevated in the melatonin-treated plants. This enzyme plays a crucial role in the biosynthesis of phenolic compounds, which are instrumental in combating oxidative stress. The recorded activity of 17.84 µM cinnamic acid min. mg-1 protein under severe drought conditions (25% of field capacity) underscores the protective role of melatonin in enhancing plant resilience.
Conclusion:The findings of this study clearly demonstrate that melatonin can serve as an effective agent in reducing the damage caused by drought stress in Moldavian balm. By enhancing photosynthetic efficiency, increasing secondary metabolite production, and boosting antioxidant enzyme activity, melatonin not only helps plants withstand unfavorable environmental conditions but also improves their overall quality and yield.
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