Effects of gamma irradiation on antioxidant enzyme activities in black carrot callus under drought stress

Daucus carota L. (carrot) is a commercially significant root vegetable widely cultivated in temperate regions for its edible taproot and valued for its high nutritional content. This study aimed to investigate the effects of drought stress on the callus tissues of Hatay black carrot (Daucus carota L. ssp. sativus var. atrorubens Alef.) genotype and to determine the impact of varying gamma radiation doses on antioxidant enzyme activities. Black carrot callus tissues were exposed to gamma irradiation at doses of 0, 7, 8, and 9 Gy to evaluate their response to drought stress. Antioxidant enzyme activities, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) as well as biochemical parameters such as hydrogen peroxide (H2O2) levels, lipid peroxidation (malondialdehyde [MDA]) content, and soluble protein concentrations, were quantified. Callus formation ceased completely at a polyethylene glycol (PEG) concentration of 15%, while a gradual decrease in callus production was observed at 5% and 10% PEG. Enzyme activity analyses revealed significant increases in CAT, SOD, and APX activities in mutant carrot callus tissues under drought stress compared with control tissues. Furthermore, drought stress resulted in elevated H2O2 and soluble protein levels, accompanied by a significant increase in lipid peroxidation (as measured by the MDA content). Multivariate analysis revealed that key oxidative stress markers and antioxidant enzymes significantly influence plant stress responses, indicating the presence of complex regulatory networks. Antioxidant systems play a central role in mitigating stress, with distinct pathways regulating oxidative damage markers independently. The findings suggest that the differences between mutant and control callus tissues under drought stress conditions may provide foundational insights for future selection studies.