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

Abstract

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 callus tissues of the Hatay black carrot (Daucus carota L. ssp. sativus var. atrorubens Alef.) genotype and to determine the impact of different 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 responses 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 measured as malondialdehyde (MDA) content, and soluble protein concentrations, were quantified. Callus formation was completely inhibited at a polyethylene glycol (PEG) concentration of 15%, whereas 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 gamma-irradiated carrot callus tissues exposed to drought stress compared with control tissues. Furthermore, drought stress resulted in elevated H2O2 and soluble protein levels, accompanied by a marked increase in lipid peroxidation, as indicated by 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 independently regulating oxidative damage markers. The results suggest that differences between gamma-irradiated callus lines and control callus tissues under drought stress conditions may provide valuable insights for future in vitro selection and stress-response studies in carrot.