Multi-Walled Carbon Nanotubes Influence on Gas Exchange, Redox Reaction and Antioxidant System in Zea mays Exposed to Excessive Copper

The carbon nanotube is one of the most encouraging tools in nanotechnology. However, the extent and interaction with different plant systems of multi-wall carbon nanotubes (MWCNT) are not fully understood under stress conditions. The present study aimed to evaluate the potential of MWCNT to improve tolerance to copper toxicity in maize (Zea mays). For this purpose, Zea mays was grown under exposure to exogenously applied MWCNT concentrations (50-100-250 mg L−1), individually or combined, with 50 μM copper (Cu stress) for 7 days. MWCNTs eliminated the adverse effects caused by stress on water status, gas parameters and osmotic potential state. Although stress activated the antioxidant system, reactive oxygen species (ROS) accumulation (hydrogen peroxide (H2O2) content) and lipid peroxidation (TBARS) increased because stress-applied maize was unable to perform an effective scavenging action. MWCNT applications had a strong ROS scavenging effect on maize seedlings. Under Cu stress, there were different responses on antioxidant capacity depending on MWCNT concentrations called the hormesis effect. Under stress, M50-M100 (50 and 100 mg L−1) reversed the radical accumulation by providing increased superoxide dismutase (SOD), glutathione peroxidase (GPX) and the regeneration of ascorbate (AsA) and glutathione (GSH). The MWCNT-activated enzyme system maintained the low levels of H2O2 and TBARS contents against stress. However, after the highest MWCNT concentration (250 mg L−1) plus stress exposure, this trend could not be continued, as by represented the disrupted antioxidant capacity and the reduced AsA/DHA and GSH redox state in maize seedlings. Therefore, the levels of H2O2 and TBARS were similar to the stress ones. Our findings indicated that MWCNT provided a new potential tool against Cu stress to improve the stress tolerance mechanism in maize.