Effect of jasmonic and salicylic acids on some antioxidants, soluble sugar and lipid peroxidation in Echinacea purpurea L. under field conditions

The most important problems of commercialization of plants, from which the secondary metabolites are extracting, are low production and high demand for their metabolites. It is so important to increase the production of secondary metabolites through boosting cultivation and processing of pharmaceutical plants. Nowadays, researchers use elicitors such as jasmonic acid and salicylic acid to increase the production of secondary metabolites that can induce physiological changes of the target living organism. Elicitors as key messenger compounds cause biosynthesis and accumulation of secondary metabolites through stimulation of plant defensive responses.
This experiment arranged as randomized complete block design with 12 treatments and three replications in Agriculture Faculty of Shahrood University of Technology in 2015-2016. The factorial arrangement was not used as it aimed at finding the best treatment combination of jasmonic acid and salicylic acid, not interpretation of nature of their interaction (29). Experimental treatments were spraying the jasmonic acid with 4 concentrations (0, 5, 20 and 50 micromolar), the salicylic acid with 3 concentrations (0, 5.0 and 1 millmolar) and spraying both of them three times with ten-day intervals, starting at reproductive stage initiation. The reason for choosing ten-day intervals was the fact that jasmonic acid remains effective only for 8 to 10 days, and the simultaneous application of jasmonic acid and salicylic acid possibly imposes antagonistic effects on plant. In this research the role of jasmonic acid and salicylic acid in increasing secondary metabolites was studied by measurement of soluble sugar, hydrogen peroxide in leaf, lipid peroxidation and antioxidants including phenols, flavonoid, anthocyanin, ascorbic acid and carotenoid.
The analysis of variance showed that different concentration of jasmonic acid and salicylic acid and spraying both of them in ten-day intervals appeared to have effect (with 99% confidence) on studied traits. For most of the treatments, the concentration of phenols, flavonoids, anthocyanin, ascorbic acid and carotenoids was higher than control. The greatest amount of ascorbic acid was observed for treatment 5 micromolar jasmonic acid with an average of 4.604 mg per gram of fresh tissue, which was 1.6 times of control. The highest amount of phenol was obtained for treatment 0.5 milimolar salicylic acid and treatment 20 micromolar jasmonic acid and 1 milimolar salicylic acid with average of 1.957 and 10.669 mg per gram of fresh tissue, respectively; the lowest value was for control with an average of 2.974 mg per gram of fresh tissue.
The result of this experiment showed that foliar spraying of jasmonic acid and salicylic acid could stimulate production and accumulation of secondary metabolites. Spraying increased antioxidant concentration in most of the treatments, and regarding to antioxidant target the appropriate concentration can be used. . Due to the fact that phenol is one of the most important metabolites, and treatment 0.5 milimolar salicylic acid increased the amount of phenol, the application of this material for Echinacea purpurea could be important, especially as it is cheap and available. Also, an increase in concentration of these antioxidant compounds caused scavenging of reactive oxygen species, delaying lipid peroxidation, enhancing chlorophyll a and b (data not presented), increasing green life span of plant, boosting number of flowers and dry weight of leaf and flower (data not presented).