The Effects of Mg Deficiency on Activities and Isoenzyme Patterns of Antioxidant Enzymes in Cotton Roots

Abstract

Magnesium (Mg) is an essential nutrient that takes vital roles in biochemical processes related to energymetabolism, regulation of enzyme activity, nucleic acid biosynthesis and carbohydrate metabolism. Mgdeficiency in arable lands is an emerging problem. Loss of balance in different metabolic pathways due toMg deficiency causes increased production of reactive oxygen species (ROS) such as O 2.- , H 2 O 2 and HO .in the roots. The aim of this work was to elucidate the antioxidant response of roots of cotton (Gossypiumhirsutum) to Mg deficiency. For this aim, antioxidant enzyme activities were measured and changes intheir isoenzymes were determined. In addition, NADPH oxidase (NOX) activity was investigated todetermine the changes in ROS signaling. Moreover, H 2 O 2 and lipid peroxidation levels were alsomeasured as an indicator of oxidative damage. Findings of this work indicate that Mg deficiency does notcause oxidative load in roots of Gossypium hirsutum plants that overwhelms cellular antioxidant defencesystem, as evident by H 2 O 2 and TBARS levels. However, to adjust to the new redox status, root cellsdrastically downregulate NOX dependent ROS production and induced total superoxide dismutaseactivity. These findings indicate that site of O 2.- production is mitochondria in roots. Although, catalaseand ascorbate peroxidase activities were decreased with Mg deficiency induced peroxidase activity seemsto limit H 2 O 2 accumulation. These adaptive responses and changes in antioxidant defence were sufficientto prevent excess ROS accumulation and occurrence of oxidative damage in roots of Gossypium hirsutumplants under Mg deficiency.