Combined effects of hypoxia and excess Mn2+ on oxidative stress and antioxidant enzymes in tomato seedlings

Abstract

Effects of high level of Mn2+ on the changes in ROS generation, root cell viability, antioxidant enzyme activities, and related gene expression in tomato (Solanum lycopersicum L., cv. Zhongza 9) seedlings were studied under normoxic and hypoxia conditions. Mn2+ concentrations, ranged between 10 and 200 μM, led to significantly higher activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APOD), glutathione reductase (GR), and also ascorbic acid (AsA) content in leaves and roots, improved root cell viability, and decreased O2·− accumulation compared with the higher Mn2+ level under hypoxia stress, which indicated that low Mn2+ could eliminate the active oxygen and protect the membrane lipid from the hypoxia hurt. When the concentration of Mn2+ reached 400–600 μM under hypoxia stress, the activities of SOD, POD, APOD, and GR and AsA content were decreased remarkably. In contrast, the MDA content was increased at the higher Mn2+ concentration. A number of antioxidant-related genes showed high expression at the lower level of Mn2+. The expression levels of SOD, POD, CAT, APOD, and GR genes were 7.95, 5.27, 3.18, 5.54, and 8.81 times compared to control, respectively. These results illustrated that the appropriate amount of Mn2+ could alleviate the detrimental effects of hypoxia stress, but reversely, the high level of Mn2+ just aggravated the existing damage to the tomato seedlings.