Zinc-oxide nanoparticles ameliorated the phytotoxic hazards of cadmium toxicity in maize plants by regulating primary metabolites and antioxidants activity

Abstract

Cadmium stress is a major threat to plant growth and survival worldwide. The current study aims to green synthesis, characterization, and application of zinc-oxide nanoparticles to alleviate cadmium stress in maize (Zea mays L.) plants. In this experiment, two cadmium levels (0, 0.6 mM) were applied to check the impact on plant growth attributes, chlorophyll contents, and concentration of various primary metabolites and antioxidants under exogenous treatment of zinc-oxide nanoparticles (25 and 50 mg L-1) in maize seedlings. Tissue sampling was made 21 days after the zinc-oxide nanoparticles application. Our results showed that applying cadmium significantly reduced total chlorophyll and carotenoid contents by 52.87% and 23.31% compared to non-stress. In comparison, it was increased by 53.23%, 68.49% and 9.73%, 37.53% with zinc-oxide nanoparticles 25, 50 mg L-1 application compared with cadmium stress conditions, respectively. At the same time, proline, superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase contents were enhanced in plants treated with cadmium compared to non-treated plants with no foliar application, while it was increased by 12.99 and 23.09%, 23.52 and 35.12%, 27.53 and 36.43%, 14.19 and 24.46%, 14.64 and 37.68% by applying 25 and 50 mg L-1 of zinc-oxide nanoparticles dosages, respectively. In addition, cadmium toxicity also enhanced stress indicators such as malondialdehyde, hydrogen peroxide, and non-enzymatic antioxidants in plant leaves. Overall, the exogenous application of zinc-oxide nanoparticles (25 and 50 mg L-1) significantly alleviated cadmium toxicity in maize. It provides the first evidence that zinc-oxide nanoparticles 25 ~ 50 mg L-1 can be a candidate agricultural strategy for mitigating cadmium stress in cadmium-polluted soils for safe agriculture practice.

Application of Zinc Oxide Nanoparticles to Mitigate Cadmium Toxicity: Mechanisms and Future Prospects

“…This increase has been associated with the stabilization of the photosynthetic apparatus, along with a reduction in oxidative damage and Cd absorption with ZnO-NPs [ 75 ]. Recently, Hussain et al [ 76 ] also found that ZnO-NPs (50 mg L −1 ) significantly enhanced chlorophyll and carotenoid synthesis under Cd stress, which ensured better synthetic efficiency, subsequently accelerating production in plant growth [ 14 ]. Heavy metals like Cd produce excessive ROS that damage the photosynthetic apparatus and reduce chlorophyll synthesis by increasing the activity of chlorophyll-degrading enzymes [ 74 , 77 ].…”

“…Cd toxicity in maize plants showed reducing effects on phenolics, flavonoids, anthocyanin, sugars, and soluble proteins. ZnO-NPs augmented the accumulation of the metabolites which helped the maize plants withstand toxic effects of Cd [ 76 ]. Applying ZnO-NPs also led to a marked increase in salicylic acid (SA) concentration in Arabidopsis thaliana L. leaves [ 150 ].…”