Evaluation of activity changes of antioxidant enzymes in saffron seedlings under cadmium stress

Plants employ various defensive strategies to cope with heavy metal stress in their growing environment. In this study, proline content, antioxidant enzyme activities, and phenolic compound levels were analyzed in saffron corms exposed to varying concentrations of cadmium stress. Saffron corms were cultivated under cadmium stress at concentrations of 0, 0.25, 0.5, 1, 2, 5, 10, and 20 mM, and samples were collected on days 0, 5, 10, 20, and 30 after cultivation. Antioxidant enzyme activities, proline levels, and phenolic content were measured. Statistical analysis was performed at a significance level of P < 0.05 using SPSS software. The results revealed significant increases in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), polyphenol oxidase (PPO), guaiacol peroxidase (GPX), phenylalanine ammonia-lyase (PAL), as well as in proline content and phenolic compound accumulation, in response to cadmium treatments. The activity responses of PPO, CAT, APX, PAL, and GPX enzymes followed a biphasic pattern, while phenolic compound accumulation exhibited a linear regression trend. In contrast, the activities of SOD and proline accumulation conformed to a flattened exponential function. Maximum activities of PPO, CAT, APX, and PAL enzymes were observed at a cadmium concentration of 10 mM in corms harvested after 30 days of stress exposure. Similarly, the highest SOD activity and proline accumulation were recorded in 30-day-old corms, with phenolic compound accumulation significantly increasing with higher cadmium concentrations, albeit with varying rates depending on the duration of exposure. The observed changes in enzyme activities during growth suggest activating regulatory mechanisms in saffron to mitigate cadmium stress. The antioxidant roles of enzymes, proline, and phenolic compounds are critical in Safran’s response to cadmium-induced stress. Given that high cadmium levels induce the production of reactive oxygen species (ROS), the saffron plant enhances the synthesis of antioxidant enzymes to neutralize destructive radicals effectively.