Shahid Bahonar University of Kerman and Iranian Biotechnology Society Agricultural Biotechnology Journal 2228-6705 18 3 2026 08 23 Combined effect of chitosan and salicylic acid hormone on physiological and biochemical traits and expression of key genes of carnosic acid biosynthesis pathway in rosemary (Rosmarinus officinalis L.) Combined effect of chitosan and salicylic acid hormone on physiological and biochemical traits and expression of key genes of carnosic acid biosynthesis pathway in rosemary (Rosmarinus officinalis L.) 1 26 5490 10.22103/jab.2026.25770.1752 FA Morteza Najafpour Mohammadabady Ph.D. Student, Department of Biology, Payame Noor University (PNU), P.O. Box 19395-4697, Tehran, Iran. 0009-0008-4220-7591 Enayatollah Yazdanpanah Assistant Professor, Department of Biology, Payame Noor University (PNU), P.O. Box 19395-4697, Tehran, Iran. 0000-0002-6437-0890 Hamid Sobhanian Associate Professor, Department of Biology, Payame Noor University (PNU), P.O. Box 19395-4697, Tehran, Iran. 0000-0003-2748-7034 Gholamreza Bakshi Khaniki Professor, Department of Biology, Payame Noor University (PNU), P.O. Box 19395-4697, Tehran, Iran. 0000-0002-8931-3649 Journal Article 2025 08 17 Objective Rosemary (Rosmarinus officinalis L.), as one of the important medicinal and aromatic plants in the pharmaceutical and food industries. Among the terpenes of rosemary, carnosic acid has gained significant importance due to its therapeutic properties such as antioxidant, antimicrobial, and antitumor effects. Consequently, researchers' attention has been drawn to the application of elicitors to enhance the growth and increase the essential oil of rosemary. Given the medicinal importance of rosemary and the potential of chitosan and salicylic acid in enhancing plant traits, this research was conducted with the aim of investigating the effect of these elicitors on rosemary traits and the expression of key genes in the carnosic acid pathway (KSLI and CPSI). Materials and methods This research was carried out as a factorial experiment based on a completely randomized design with three replications. Three months after transplanting the seedlings, chitosan (Ch) at concentrations of 10, 50, and 100 mg/L and salicylic acid (SA) at concentrations of 5, 10, and 20 µM were applied individually and in combination, in three stages at three-week intervals, as foliar sprays on the aerial parts of rosemary. Physiological and biochemical traits and expression of key genes of carnosic acid biosynthesis pathway were measured one week after the last spraying. Results The treatment combinations had synergistic effects on rosemary traits. As the most effective treatments, SA 10 µM + Ch 100 mg/L and SA 20 µM + Ch 50 mg/L treatments led to a 44 and 45% significant decrease in MDA, 2 and 2.5-fold significant increase in phenol, 2.8 and 2.9-fold increase in sugars, 2.6 and 2-fold increase in catalase activity, 2.8 and 2.5-fold increase in SOD activity, 2 and 2.3-fold increase in polyphenol oxidase activity, 3 and 1.9-fold increase in chlorophyll content, 2 and 2.2-fold increase in carotenoid content, 2.3 and 2.6-fold increase in essential oil content, 3 and 3.6-fold increase in CPSI gene expression, 3.4 and 3.6-fold increase in KSLI gene expression, respectively. Conclusions Combined treatments significantly reduce lipid peroxidation and increase pigments, the antioxidant system, essential oil, and the expression of key genes in the carnosic acid pathway. Objective Rosemary (Rosmarinus officinalis L.), as one of the important medicinal and aromatic plants in the pharmaceutical and food industries. Among the terpenes of rosemary, carnosic acid has gained significant importance due to its therapeutic properties such as antioxidant, antimicrobial, and antitumor effects. Consequently, researchers' attention has been drawn to the application of elicitors to enhance the growth and increase the essential oil of rosemary. Given the medicinal importance of rosemary and the potential of chitosan and salicylic acid in enhancing plant traits, this research was conducted with the aim of investigating the effect of these elicitors on rosemary traits and the expression of key genes in the carnosic acid pathway (KSLI and CPSI). Materials and methods This research was carried out as a factorial experiment based on a completely randomized design with three replications. Three months after transplanting the seedlings, chitosan (Ch) at concentrations of 10, 50, and 100 mg/L and salicylic acid (SA) at concentrations of 5, 10, and 20 µM were applied individually and in combination, in three stages at three-week intervals, as foliar sprays on the aerial parts of rosemary. Physiological and biochemical traits and expression of key genes of carnosic acid biosynthesis pathway were measured one week after the last spraying. Results The treatment combinations had synergistic effects on rosemary traits. As the most effective treatments, SA 10 µM + Ch 100 mg/L and SA 20 µM + Ch 50 mg/L treatments led to a 44 and 45% significant decrease in MDA, 2 and 2.5-fold significant increase in phenol, 2.8 and 2.9-fold increase in sugars, 2.6 and 2-fold increase in catalase activity, 2.8 and 2.5-fold increase in SOD activity, 2 and 2.3-fold increase in polyphenol oxidase activity, 3 and 1.9-fold increase in chlorophyll content, 2 and 2.2-fold increase in carotenoid content, 2.3 and 2.6-fold increase in essential oil content, 3 and 3.6-fold increase in CPSI gene expression, 3.4 and 3.6-fold increase in KSLI gene expression, respectively. Conclusions Combined treatments significantly reduce lipid peroxidation and increase pigments, the antioxidant system, essential oil, and the expression of key genes in the carnosic acid pathway. https://jab.uk.ac.ir/article_5490_c900ced7451da79502d29aa37ebb7b60.pdf