Comparative effects of ascobin and glutathione on copper homeostasis and oxidative stress metabolism in mitigation of copper toxicity in rice.

Copper (Cu)-pollution of agricultural lands is a big threat to crop production. Exogenous chemical treatment is an easily accessible and instant approach to remediate metal toxicity, including Cu-toxicity in plants. We compared the effects of ascobin (ASC, ascorbic acid:citric acid at 2:1) and glutathione (GSH) in mitigation of Cu-toxicity in rice. Plants subjected to Cu-stress displayed growth inhibition and biomass reduction which were connected to declined levels of chlorophylls, relative water content (RWC), total phenolic compounds, carotenoids and Mg2+ . An increased accumulation of reactive oxygen species (ROS) and malondialdehyde indicated an evident oxidative stress in Cu-stressed plants. However, application of ASC or GSH minimized the inhibitory effects of Cu-stress on rice plants by restricting Cu2+ uptake, and improving mineral balance, chlorophyll contents and RWC. Both ASC and GSH pretreatments reduced the levels of ROS and malondialdehyde, and improved the activities of antioxidant enzymes, suggesting their alleviating roles against oxidative damage. A comparison on the effects of ASC and GSH under Cu-stress revealed that ASC was more effective in restricting Cu2+ accumulation (69.5% by ASC and 57.1% by GSH), Ca2+ and Mg2+ homeostasis, protection of photosynthetic pigments, and activation of antioxidant defense mechanisms [catalase (110.4%), ascorbate peroxidase (76.5%) and guaiacol peroxidase (39.0%) by ASC, and catalase (58.9%) and ascorbate peroxidase (59.9%) by GSH] in rice than GSH, and eventually resulting in better protection of ASC-pretreated plants against Cu-stress. In conclusion, although ASC and GSH differed in induction of stress protective mechanisms, both were effective in improvement of rice performance against Cu-phytotoxicity.