Elicitors, particularly salicylic acid, by stimulating plant defense pathways, can enhance the production of secondary metabolites and improve morphological, physiological, and biochemical traits. This study aimed to investigate the effects of growth regulators and salicylic acid elicitation on callus induction and its various characteristics in Chrysanthemum plant. After seed sterilization and culture on MS medium, leaf and stem explants from young plants were prepared and cultured in media containing different growth regulator treatments, including H1 (control), H2 (1 mg NAA + 2 mg BAP), H3 (0.2 mg 2,4-D), H4 (0.2 mg BAP + 0.5 mg 2,4-D), and H5 (2 mg BAP + 2 mg 2,4-D). The experiment was conducted as a factorial arrangement in a completely randomized design with three replications, two types of explants, and two light conditions. After selecting the optimal treatment, different concentrations of salicylic acid (0, 50, 100, and 150 µM) were applied to the obtained callus. After four weeks, traits such as callus induction percentage, initiation time, fresh and dry weight, and callus volume were measured. The highest callus induction percentage (99.66%), shortest initiation time, and greatest fresh weight, dry weight, and callus volume were observed in treatment E1H5L (leaf explant, 2 mg BAP + 2 mg 2,4-D, light condition). Furthermore, the effects of different salicylic acid concentrations on traits including chlorophyll content, carotenoids, flavonoids, phenolics, antioxidant capacity, malondialdehyde, proline, anthocyanin, and the activity of catalase and peroxidase enzymes were evaluated. Results indicated that increasing salicylic acid concentration up to 100 µM significantly enhanced fresh weight, dry weight, and callus volume, reaching maximum values of 2.04 g, 1.134 g, and 1.22 mm³, respectively. Salicylic acid treatments also increased photosynthetic pigments, including chlorophyll a and b and carotenoids, with the highest levels observed at 100 µM. The amounts of phenolic and flavonoid compounds, as well as antioxidant activity, were markedly elevated, especially at 150 µM. Additionally, malondialdehyde content, proline, anthocyanin, and antioxidant enzyme activities (catalase and peroxidase) increased in response to salicylic acid, indicating its potential role in stimulating defense mechanisms and stress tolerance in callus. Overall, the 100 µM salicylic acid treatment had the most positive impact on callus growth and biochemical traits, whereas the 150 µM treatment showed the greatest effect on activating defense plant mechanisms. |
