Changes in some antioxidant enzymes and physiological indices of purple coneflower (Echinacea purpurea L.) in response to water deficit and foliar application of salicylic acid and spermine under field condition

Echinacea purpurea is an important industrial and ornamental plant that its quality and physiological parameters may be negatively affected by drought, however, negative effects of drought could be reversed by application of plant growth regulators such as salicylic acid (SA) and spermine (SPM). Therefore, this experiment was conducted to investigate the effects of irrigation regimes (irrigation after 20, 40 and 60% soil water depletion) and, SA and SPM treatments (no spray, 75 mg L−1 SA, 150 mg L−1 SA, 70 mg L−1 SPM, 75 mg L−1 SA + 70 mg L−1 SPM and 150 mg L−1 SA + 70 mg L−1 SPM) on the activities of antioxidant enzymes catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and superoxide dismutase (SOD), shoot dry mass (SDM), chlorophyll (Chl), carotenoid (Caro), proline (Pro), phenol, flavonoid and Malondialdehyde (MDA) in purple coneflower (Echinacea purpurea L.). Water deficit increased the activities of enzymes, and the contents of carotenoids, proline, MDA, phenol and flavonoid while it decreased chlorophyll content and shoot dry mass. Among tested enzymes, CAT showed the highest increase in response to water deficit. SA and SPM application increased antioxidant enzymes activities, shoot dry mass and the contents of chlorophyll, carotenoid, proline and flavonoid (only by SA application), but decreased phenol and MDA contents. SOD was the most responsive enzyme to SA and SPM. However, the magnitude of SA and SPM effects was dependent on the level of soil available water. The positive effects of SA were greater than those of SPM. The superiority of SA over SPM was more pronounced at higher level of water deficit. The effects of SA application were greater at 150 than at 75 mg L−1. The highest plant biomass was produced under combined application of SA and SPM. These results indicated that SA and SPM improve purple coneflower growth under water deficit by stimulating antioxidant defense system, alleviating lipid peroxidation and increasing osmotic adjustment. The results also suggest that growers can use SA and SPM to increase productivity of purple coneflower under drought stress.