Hormetic Effects of Low Dose Gamma Irradiation on Antioxidant Defense System and Thymol Biosynthesis in Thyme Plants

This study investigated the impact of different doses (0, 1, 3, and 5 Gy) of gamma radiation on antioxidant mechanisms and thymol biosynthesis in Thymus vulgaris. Concentration of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) exhibited dose-dependent increases, indicating oxidative damage and a time-dependent progression of stress. Superoxide dismutase (SOD) activities were triggered in response, accompanied by time-dependent variations in peroxidase (POD) and polyphenol oxidase (PPO) activities. Biochemical analyses revealed enhanced total phenolic content (TPC), total flavonoid content (TFC) and anthocyanin levels at 1 Gy. Additionally, the effect of radiation on the expression of pivotal genes in the biosynthesis pathway of thymol, such as DXR, TvTPS, and CYP71D178, was investigated. Gamma irradiation significantly up-regulated DXR transcription at higher doses, while TvTPS and CYP71D178 transcription peaked at 1 Gy. Thymol emerged as the predominant compound in the essential oil composition, experiencing a significant increase at 1 Gy, thus illustrating a hormetic response. This study provides scientific insights into the hormesis effects of gamma irradiation on antioxidant responses and thymol biosynthesis in Thymus vulgaris, contributing to a better understanding of the complicated biochemical processes involved in plant adaptation to radiation stress.