Özet:

Magnesium (Mg) is an essential nutrient that takes vital roles in biochemical processes related to energy metabolism, regulation of enzyme activity, nucleic acid biosynthesis and carbohydrate metabolism. Mg deficiency in arable lands is an emerging problem. Loss of balance in different metabolic pathways due to Mg deficiency causes increased production of reactive oxygen species (ROS) such as O2.-, H2O2 and HO. in the roots.  The aim of this work was to elucidate the antioxidant response of roots of cotton (Gossypium hirsutum) to Mg deficiency. For this aim, antioxidant enzyme activities were measured and changes in their isoenzymes were determined. In addition, NADPH oxidase (NOX) activity was investigated to determine the changes in ROS signaling. Moreover, H2O2 and lipid peroxidation levels were also measured as an indicator of oxidative damage. Findings of this work indicate that Mg deficiency does not cause oxidative load in roots of Gossypium hirsutum plants that overwhelms cellular antioxidant defence system, as evident by H2O2 and TBARS levels. However, to adjust to the new redox status, root cells drastically downregulate NOX dependent ROS production and induced total superoxide dismutase activity. These findings indicate that site of O2.- production is mitochondria in roots. Although, catalase and ascorbate peroxidase activities were decreased with Mg deficiency induced peroxidase activity seems to limit H2O2 accumulation. These adaptive responses and changes in antioxidant defence were sufficient to prevent excess ROS accumulation and occurrence of oxidative damage in roots of Gossypium hirsutum plants under Mg deficiency

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