Effects of Different Salicylic Acid Doses on the Expression of Antioxidant Defense Genes in Pepper (Capsicum annuum L.)

Salicylic acid is a signaling molecule and a type of phenolic compound involved in the regulation of growth, development, and defense responses. Effects of salicylic acid on the antioxidant defense system have been examined under stress conditions, but the fundamental actions of varying doses of salicylic acid on antioxidant gene expression in unstressed plants are yet to be fully clarified. This study aimed to determine the effects of 0, 0.5, and 1 mM salicylic acid treatments on the expression levels of SOD, CAT, APX, and POD genes in the leaves of Capsicum annuum L. cv. ‘Postal’ grown under well-watered conditions, using RT-qPCR. Gene expression levels were determined using the 2^-ΔΔCt method with respect to UBI3 as a reference gene. Results showed that differential responses of the analyzed genes were dose and target gene specific. The 0.5 mM SA application had a suppressive effect on the expression of the SOD and APX genes while the 1 mM SA application significantly up-regulated the SOD, CAT and APX genes (P0.05). Based on these results, salicylic acid has a dose-dependent gene-specific effect on the transcriptional regulation of antioxidant defense genes in pepper.