en Melatonin-mediated improvement of ionic homeostasis and antioxidant defense ‎enhances salinity tolerance in Damask Rose (Rosa damascene)‎ تنش شوري Salt Stress پژوهشي Research <div style="text-align: left;"><span style="font-size:12pt"><span style="font-family:&quot;Times New Roman&quot;,serif"><b><span style="font-size:10.0pt">This study investigated the role of melatonin in alleviating salinity stress in <i>Rosa damascena</i>. A factorial experiment was conducted in a completely randomized design with three replications, combining four salinity levels (0, 60, 120, and 180 mM NaCl) and three melatonin concentrations (0, 150, and 250 &mu;M). Salinity significantly inhibited shoot and root growth, reduced chlorophyll and carotenoid contents, and decreased relative water content (RWC), while increasing electrolyte leakage, proline, malondialdehyde (MDA), and sodium accumulation. Melatonin application significantly alleviated these adverse effects. Under non-saline conditions, 250 &mu;M melatonin enhanced chlorophyll <i>a</i> and carotenoids by 23.8% and 57.6%, respectively, compared with the control, and significantly increased antioxidant enzyme activities, particularly superoxide dismutase (SOD) and catalase (CAT). Similarly, at moderate salinity levels (60&ndash;120 mM), 250 &mu;M melatonin maintained high enzyme activity and improved potassium retention. However, under severe salinity (180 mM NaCl), 150 &mu;M melatonin was more effective in maintaining water balance, reducing ion leakage by up to 20%, lowering MDA by 31%, and decreasing Na⁺ accumulation by up to 53%. The shift in optimal concentration from 250 &mu;M under non-saline or mild stress to 150 &mu;M under severe stress reflects the plant&rsquo;s adaptive regulation, where higher melatonin enhances growth under optimal conditions, whereas moderate levels suffice to activate antioxidant defenses and maintain ionic balance under stress. Overall, melatonin within the 150 &ndash;250 &mu;M range effectively enhanced antioxidant activity, ionic homeostasis, and salinity tolerance in <i>R. damascene</i></span></b><span style="font-size:10.0pt">.</span></span></span></div> <span style="font-size:12pt"><span style="font-family:&quot;Times New Roman&quot;,serif"><b><span style="font-size:10.0pt">This study investigated the role of melatonin in alleviating salinity stress in <i>Rosa damascena</i>. A factorial experiment was conducted in a completely randomized design with three replications, combining four salinity levels (0, 60, 120, and 180 mM NaCl) and three melatonin concentrations (0, 150, and 250 &mu;M). Salinity significantly inhibited shoot and root growth, reduced chlorophyll and carotenoid contents, and decreased relative water content (RWC), while increasing electrolyte leakage, proline, malondialdehyde (MDA), and sodium accumulation. Melatonin application significantly alleviated these adverse effects. Under non-saline conditions, 250 &mu;M melatonin enhanced chlorophyll <i>a</i> and carotenoids by 23.8% and 57.6%, respectively, compared with the control, and significantly increased antioxidant enzyme activities, particularly superoxide dismutase (SOD) and catalase (CAT). Similarly, at moderate salinity levels (60&ndash;120 mM), 250 &mu;M melatonin maintained high enzyme activity and improved potassium retention. However, under severe salinity (180 mM NaCl), 150 &mu;M melatonin was more effective in maintaining water balance, reducing ion leakage by up to 20%, lowering MDA by 31%, and decreasing Na⁺ accumulation by up to 53%. The shift in optimal concentration from 250 &mu;M under non-saline or mild stress to 150 &mu;M under severe stress reflects the plant&rsquo;s adaptive regulation, where higher melatonin enhances growth under optimal conditions, whereas moderate levels suffice to activate antioxidant defenses and maintain ionic balance under stress. Overall, melatonin within the 150 &ndash;250 &mu;M range effectively enhanced antioxidant activity, ionic homeostasis, and salinity tolerance in <i>R. damascene</i></span></b><span style="font-size:10.0pt">.</span></span></span> Antioxidant enzymes, Carotenoids, Electrolyte leakage, Lipid peroxidation, Proline Antioxidant enzymes, Carotenoids, Electrolyte leakage, Lipid peroxidation, Proline 35 44 http://jispp.iut.ac.ir/browse.php?a_code=A-10-324-13&slc_lang=en&sid=1 Roya Zomorodnia Roya Zomorodnia royazomorodnia7@gmail.com No Department of Horticultural Sciences, Faculty of Agricultural Sciences, Sari Agricultural Sciences and ‎Natural Resources University, Sari, Iran Department of Horticultural Sciences, Faculty of Agricultural Sciences, Sari Agricultural Sciences and ‎Natural Resources University, Sari, Iran Mahnaz Karimi Mahnaz Karimi karimi1320@gmail.com Yes Department of Horticultural Sciences, Faculty of Agricultural Sciences, Sari Agricultural Sciences and ‎Natural Resources University, Sari, Iran Department of Horticultural Sciences, Faculty of Agricultural Sciences, Sari Agricultural Sciences and ‎Natural Resources University, Sari, Iran Mehrnaz Hatami Mehrnaz Hatami Hatamimehrnaz@gmail.com No Department of Medicinal Plants, Faculty of Agriculture and Environment, Arak University, Arak, Iran Department of Medicinal Plants, Faculty of Agriculture and Environment, Arak University, Arak, Iran