Phytohormonal Regulation of Antioxidant Systems in Petals of Drought Stressed Pot Marigold (Calendula officinalis L.)

Drought is an important abiotic stress limiting plant performance. Generation of reactive oxygen species (ROS) is enhanced under stresses. Two greenhouse experiments were conducted to evaluate the effect of phytohormones on the changes of antioxidant enzymes and carotenoids in petals of pot marigold (Calendula officinalis L.) under drought stress. Results showed that the activities of superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6) increased 47 and 73%, respectively, in petals under water deficit conditions compared with the control plants. Spraying with gibberellic acid (GA3) and benzyl amino purine (BAP) alleviated drought effects, but application of abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA) and brassinolid (BR) induced the activity of these enzymes. In the case of peroxidase (POD, EC 1.11.1.7), GA3 enhanced the enzyme activity unlike the other enzymes and the rest of the phytohormones had no significant effect on POD activity under either stressed or non-stressed condition. Concentration of carotenoids was affected by drought and hormone treatments. Concentration of carotenoids increased under water deficit but, GA3, BAP and JA had inhibitory effects on lycopene and carotene synthesis, while the rest of the hormones increased them. Spraying with GA3 increased luteoxanthin concentration in petals by 35 and 20% in comparison with the non-stressed and stressed environments, respectively. The decrease in POD activity under stress suggests that other mechanisms might be involved for ROS scavenging in petals of pot marigold.